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A BEHAVIORAL AND PERCEPTUAL STUDY OF
CAT FLEA LARVAE,Ctenocephalides felis, AND
THEIR RESPONSES TO VARIOUS STIMULI
THOMAS MATTHEW DYKSTRA
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
This dissertation is dedicated to the Angels we know as 'Guardians'.
My prayerful thanks must first extend to Mr. Richard Fox. His support both
during and after my doctoral degree leave me thankful that God has placed him into this
My committee members have been uncharacteristically helpful in their
suggestions, their advice, and most importantly their discussions. They have helped me
to reach a scientific level of inquiry that I would have been otherwise unable to reach.
A special note of thanks must extend to Dr. Phil Callahan who took me under his
guidance and tolerated much on my behalf. He has supplied me with dozens of books to
read, as well as hundreds of reference materials from his own extensive library. He has
graciously offered his own laboratory space for my benefit, and is always lending me an
ear for my questions. His knowledge of the world, especially physics and entomology,
has been a continuous fountain whereby I ask for a cupful, but he draws for me a
bucketful. Our weekly luncheons, our out-of-state trips together, and our moments of
prayer with his wife, Winnie, will forever by etched into my soul. It is my hope that
someday I may be worthy enough to untie his sandalstrap.
TABLE OF CONTENTS
ACKNOWLEDGMENTS ............................................. iii
ABSTRACT ...................................................... vi
1 INTRODUCTION ................... ..... .............. 1
2 LITERATURE REVIEW 1- GENERAL ............................. 6
Insect Antennae: an Overview ............... .................. 6
Insect Antennae as Possible Electromagnetic Receivers ....... 11
Antennal Variety ................................. 19
Insect Sensilla: an Overview .................................. 21
Antennae Fundamentals ................ ................... 25
Coupling and Arrays ............................... 31
Dielectric Waveguides .............................. 33
Insect Sensilla and Radiation Detection ................... 36
Piezoelectric and Pyroelectric Properties of Insect Cuticle .......... 42
Dielectric Antennae: Possible Function in Insects .................. 46
Scatter Surfaces ......... .................. ............ .50
Electromagnetics: an Overview ................................ 56
Animal Perception ................ ................62
Detection of Electromagnetic Fields by Insects .............. 66
Response of Insects to Electromagnetic Fields .............. 72
Electrical fields ............................... 78
Magnetic fields .............................. 82
Termite biofields .............................. 86
Magnetic field detection ......................... 89
Molecular emissions ............................ 96
3 LITERATURE REVIEW 2- FLEAS ............................... 111
Ecology of Fleas .......................................... 111
The Cat Flea ......................................... 121
4 MATERIALS AND METHODS .................................... 125
Flea Colony ....................................... ......... 125
Experimental Conditions ..................................... 127
Data Acquisition .......................................... 129
Height Experiments ............................................ 132
Electromagnetic Field Experiment ............................... 133
Magnet Experiments ................... ..................... 133
Fan Experiments ...................... ................... .... 135
Competing Human Stimuli .................................... 135
Statistical Analysis ................... ................... ..... 136
External Morphology ................... .................... 138
5 PILOT EXPERIMENTS ........... ...... ....................... .. 139
Introduction .................................... .. .......... 139
The Experiments ..................... ................... ... 140
C conclusions ..................................... .......... 147
6 RESULTS ......................................................... 149
M miscellaneous Experiments ................................... 149
Height Experiments ................... ................... .. 149
Number Experiments .................................... .. .... 150
Magnetic Experiments .................. ...................... 151
Magnet 10 Experiments ........................................ 153
Fan Experiments ................... ....................... 154
Breakdow n D ata .................................... ........... 154
Electromagnetic Field Experiment ........................... ..... 156
Competing Human Stimuli ....................................... 158
External Morphology ................... ................... .. 158
Gross Anatomy ....................................... 158
Electron M icrographs ..................................... 159
7 DISCUSSION ............. ........................................ 212
The Antennae ................... ... ...................... 215
Body Setae ................................................... 221
Scattering ..................... .. .............. ............ 226
Molecular Emissions ................... ..................... 228
Fleas and Electromagnetism ...................................... 229
APPENDIX- ADDITIONAL BREAKDOWN DATA ............................... 231
REFERENCES .............................. ................... ........... 264
BIOGRAPHICAL SKETCH ...................... .. ................. ..... 289
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
A BEHAVIORAL AND PERCEPTUAL STUDY OF
CAT FLEA LARVAE, Ctenocephalides felis, AND
THEIR RESPONSES TO VARIOUS STIMULI
Thomas Matthew Dykstra
Chairman: Dr. Philip S. Callahan
Major Department: Entomology and Nematology
Cat flea larvae, Ctenocephalides felis, were found to exhibit an orientation
response toward a human stimulus. This is the first report describing this behavior in the
cat flea larva. The response was first observed and tested throughout this study in a
covered plastic petri dish, and was determined to occur over relatively short distances of
up to 2 meters from a human being sitting in a chair. The orientation response could be
enhanced by increasing the numbers of cat flea larvae in an experiment.
Cat flea larvae were additionally found to react to magnetic fields of
approximately 750 Gauss and electric field intensities of 4.1 x 10-3 V/m, which were
discovered to alter the orientation response if tested in conjunction with a human
stimulus. The presence of two types of magnets when placed between the fleas and the
human stimulus adversely affected the orientation response, which resulted in random
movement about the petri dish. The same result was achieved with wind produced from a
small fan positioned so as to pass air across the surface of the petri dish. Random
behavior, or non-directional movement, was additionally noted when the flea larvae were
placed above head level. Cat flea larvae could locate and orient to a human stimulus
below head level, but the response was reduced at much lower levels such as ground
The cause of this orientation response may be mediated in part or in whole by
electromagnetic frequencies of unknown origin. This possibility was theoretically
analyzed in reference to external larval morphology. The cat flea's body as well as two
of its components, the antenna and the body setae, are certainly capable of receiving
complex electromagnetic messages. Detection of electromagnetic radiation may be
operating individually or in concert. The possible occurrence of electromagnetic field
detection for an insect is discussed with an extensive literature review outlining possible
The cat flea. Ctenocephalidesfelis, is one of the most important pests in the urban
environment. Large volumes of research have been devoted to its management,
especially around the home. The majority of this research focuses on insecticides, which
are the most common means of managing adult flea populations. Behavioral studies on
the adult cat flea are rare and often highly anecdotal. Even less has been published on the
behavior of cat flea larvae, and virtually nothing has been published concerning their
responses to normal and artificial stimuli.
This dissertation investigates a newly found behavior of the cat flea larva, that
being its very strong orientation response toward a human being. The behavior was an
unexpectedly pleasant discovery that I observed in the laboratory back in 1994. I became
intrigued with this behavior and decided to build a research dissertation around it.
Pilot experiments were initiated in order to characterize this behavior and to
ascertain what limitations it exhibited. These pilot experiments answered some questions
and, as expected, raised some more. Data acquisition was limited to behavioral
observations only. A review of the pilot experiments is the subject of Chapter 5. Based
upon the results of the pilot experiments, a research plan was devised that included the
number of larvae to use in an experiment, the age of the larvae, and the time limit within
which all experiments should be conducted. It also became apparent to me that
electromagnetic fields may be linked to this behavior, hence, a large part of the
experiments and discussion are devoted to this subject.
A simple listing of my results in order to draw obvious conclusions is a procedure
I carried out for my Master's degree. Speculating upon the implications of my research,
and then probing a wide variety of fields in order to help explain them, is more
appropriate for a doctoral level student. The results reported in Chapter 6 are
straightforward and relatively easy to follow. However, after the science is reported, the
philosophy should begin, after all a Ph.D. is a philosophy degree. Probing questions and
the assimilation of literature from all over the world should be, and will be, a primary
focus of this dissertation. The most important question to ask is not "What is going on?"
but rather "What do I think is going on?".
Entomology and electromagnetics are not often found together in the literature.
For this reason, a thorough review and analysis of the pertinent literature not only
discussing these two areas, but integrating these two areas, is absolutely necessary. The
general literature review (Chapter 2) begins with an analysis of insect antennae and their
possible role as electromagnetic receivers. This background information will help the
reader understand why the antennae of cat flea larvae, as revealed by scanning electron
microscopy, could very well be electromagnetic receivers with a high degree of
directionality inherent in their structure.
The general literature review will continue with an analysis of insect sensilla,
emphasizing their external morphology. Following this is a discussion of basic antennal
properties including the effects of antennal arrays, as well as the characteristics of a
special type of non-conducting antenna known as a dielectric waveguide. This discussion
will tie back in with insect sensilla, thus helping the reader to better understand the link
between electromagnetic antennae and insect sensilla.
A review discussing piezoelectric/pyroelectric properties of the insect cuticle
relates directly to the detection of various environmental stimuli. This inherent property
of insect cuticle will help to explain how stimuli can be received and eventually perceived
by an organism without the benefit of distinct sensory organs.
A discussion of the role of antennae in receiving electromagnetic signals would
not be complete without a knowledge of the "surface terrain" surrounding an antenna, for
this profoundly influences the electrical properties of the antenna and how radiation is
received by that antenna. The phenomenon is called "scattering" and volumes of
literature have been written about a subject I only wish to introduce to the reader. The
presence of spines on the body of flea larvae, their morphological similarity to dielectric
antennae, and the odd surface terrains found on flea larval cuticle, especially that region
directly surrounding the spines, all strongly suggest an electromagnetic function. The
brief review on scattering found in Chapter 2 (entitled "Scatter Surfaces") will provide
the necessary background for the reader to appreciate the importance of scattering and
how cat flea larvae may use this physical phenomenon for sensing their environment.
The most comprehensive section of the general literature review will focus on
electromagnetic energy due to its large emphasis in the experiments. An overview of the
electromagnetic spectrum is an appropriate start, while a consideration of the detection of
electromagnetic energy in insects and other animals will follow. These sections will give
the reader a taste of the incredible diversity of literature in this field. Many animals show
remarkable sensitivities to electromagnetic fields, therefore this section will show that
there are "precedents" within Kingdom Animalia. Many studies referred to in this
dissertation will be based upon the experiments and insights of scientists who have spent
their entire careers studying electromagnetic phenomena and their concomitant effects
The final part of Chapter 2 will focus on specific studies whereby insects respond
to individual electric, as well as magnetic, fields. These sections will introduce key
points that lead in to the documented occurrence of"biofields" in termites. There are
interesting differences, as well as striking similarities between termite biofields and cat
flea larval aggregation and orientation behavior.
How magnetic fields are or may be detected by organisms, especially insects, will
be the subject of the next section. Because electrical and magnetic fields possess distinct
properties, their detection and perception by insects may be just as distinct. It is not
likely that magnetic fields are detected exclusively by dielectric waveguides. Instead,
research suggests that magnetic fields are probably detected internally and indirectly due
to their effects upon physiological systems.
The detection of electromagnetic signals may not only stem from the
environment, but from molecules as well. Emissions from airborne molecules originate
from molecular bonds that absorb and emit radiation, usually in the infrared, because of
vibrations and stretching of bond lengths. The analysis of these molecular emissions
helps to identify exactly the molecule in question since each molecule possesses its own
infrared "fingerprint". This part of the literature review will introduce and then develop
the hypothesis that insects may detect molecular emissions, thus helping them to
positively identify a molecule. The possibility that fleas use a similar system will be
discussed in Chapter 7.
Chapter 3 is a short review of the literature devoted entirely to fleas, the subject of
my research. It begins with a discussion of the ecology of fleas with an emphasis on
larval habitat and feeding strategies. Following this will be a specific review of the cat
flea showing its dependence upon the host for its survival. The focus of this section will
strive to emphasize how vital it is for the cat flea immatures to obtain a blood meal and
how this may relate to host detection. This last point leads directly into my dissertation
research, and why cat flea larvae may be homing in to such an unnatural host as a human
The experimental results appear in Chapter 6, while the discussion section
constitutes Chapter 7.
LITERATURE REVIEW 1- GENERAL
Insect Antennae: an Overview
If the doors of perception were cleansed everything would appear to man
as it is, infinite. For man has closed himself up till he sees all things
through narrow chinks of his cavern."
Many entomology textbooks place an enormous emphasis on airborne molecules
and their role in influencing insect behavior over great distances. Giant saturniid moths
were the subject of popular stories because of the documented cases, repeated perhaps
thousands of times by amateurs the world over, in which one caged female would release
a sex pheromone and thus attract hundreds of potential male suitors (Fabre, 1913).
Because research suggests that the ability to detect these molecules is intimately tied to
proper functioning of the antennae, antennal morphology is worthy of close examination.
If the molecules adhered to a surface, any surface, then the greater the surface area
of the antenna, the greater the probability that a molecule will selectively adhere to it.
The bipectinate antennae of the saturniid moths do admittedly exhibit an enormous
surface area increase over more filiform type antennae (compare Figs. 2-la,b with Fig. 2-
2a). However, the differences in antennal shape and the size and spacing of olfactory
hairs do not appear to affect the deposition velocity significantly (Mankin and Mayer,
(c) (d) (e) (f)
Figure 2-1. Diversity of insect antennae (redrawn from various sources). (a) filiform,
Blattodea; (b) filiform, Hemiptera; (c-e) capitate (clubbed), Coleoptera; (f)
capitate, Lepidoptera; (g) geniculate (elbowed), Hymenoptera; (h) pectinate,
Coleoptera: Pyrochroidae; (i) plumose, Diptera: Culicidae.
N(V 1 ^(3)
Figure 2-2. Bipectinate antenna of Hyalophora cecropia (Lepidoptera: Saturniidae). (a) full antenna [redrawn from cover
photograph of the Journal of Applied Optics, Vol. 7]; (b) close-up of trichoid sensillae. (1) first level of proposed
electromagnetic detection, the stalk; (2) second level, the branching hairs; (3) third level, the sensillae.
1984). If molecules do not adhere at different rates according to the shape of a given
antenna, then how does one explain the various antenna shapes pictured in Figure 2-1?
Insects have survived with very large antennae, such as Cerambycid beetles who
may have antennae several centimeters long; or very small antennae, such as the tiny
Trichogramma parasitic wasps whose antennae can only be seen with the aid of a
microscope. The calliphorid fly, Chrysomya rufifacies, has been found to be attracted to
a cadaver in less than 10 minutes (Byrd, pers. comm.'), even though their antennae are
small in relation to other insects (Figure 2-3) and contain only a small hair called an
"arista" after which the antenna is named. The role of antennal surface area for assisting
the insect in detecting airborne molecules was an argument that carried little weight.
A second glance at all of the antennal types shown in Figure 2-1, reveals that most
of them look like poor 'molecular nets', in the sense of capturing airborne molecules
from the atmosphere, if indeed that is their main function. If antennae have one function,
to capture airborne molecules, they should all look relatively the same, because this
common function would bind them morphologically. However, insects do not all possess
the same morphological type of antennae. Therefore, one may speculate that there are
varying functions attributed to each, and if so, these alternate functions should help
dictate the final shape of the antenna.
1Jason Byrd, graduate student in forensic entomology at the University of
Florida, personal conversation dated October 1, 1997.
Figure 2-3. Aristate antennae (Diptera) (a) head of Calliphorid fly showing size of
antennae relative to head [redrawn from Eickwort, 1984](b) Sarcophagidae; (c)
Calliphoridae (d) Tachinidae.
Insect Antennae as Possible Electromagnetic Receivers
The suggested receiver for electromagnetic radiation is commonly held to be the
insect's antennae (Laithwaite, 1960; Callahan, 1967; Corbiere-Tichane, 1971, 1974;
Corbibre-Tichan6 and Bermond, 1972). Much like the former chemosensory hypothesis,
so prevalent in entomological circles, this one is absolutely dependent upon antennal
morphology, but it views the antennae as morphological structures for tuning in to certain
frequencies, and not as an atmospheric "net" for capturing molecules from the air.
Laithwaite (1960) calculated that the moth Orgyia antiqua has functioning
electromagnetic antennae that, due to the spacing of the pectinations, responded to
wavelengths between 20 and 200 pm.
Electromagnetic antennal science is extremely complicated. If one wishes to
pursue the reasons why some electromagnetic antennae work better than others, a
comprehensive background in calculus is required. Even simple layman's terms, as
spelled out in an introductory book for radio amateurs (The ARRL Antenna Book, 1974),
left my head spinning at times. Therefore, these complex reasons will not be
mathematically discussed in this dissertation. What can and will be discussed is the
theory behind antennas, which is wonderfully discussed in Kiely's 1953 book entitled
"Dielectric Aerials". The saturniid male antenna displayed in Fig. 2-3a takes on a very
different viewpoint after reading these two books as well as other books discussing
electromagnetic receivers. For example, there are three "levels" of detection for this type
of antenna based on only the most fundamental antennal rules.
The first level focuses on the main stalk as an electromagnetic (EM) receiver. The
second focuses on the individual hairs stemming from the stalk as EM receivers. The
third reduces to the level of the sensillum on those individual hairs (all levels displayed in
Figure 2-2). A successful argument may even be made for a more complicated fourth
level, that being the successful integration of two or more of these levels.
If the length of the stalk of the antennae itself were 1 cm, then the stalk would
resonate when exposed to an -MNI frequency with a wavelength of 1 cm. It may also
resonate to frequencies of 2, 3, 4, 5, or even 6 cm since antennae commonly pick up
multiples of the primary frequency. For the same reason, wavelengths /2, 1/3, 1/4, 1/5.
and 1/6 would work reasonably well. The U.S. Navy communicated with its submarines
with an antenna perfectly tuned to only 1/10 of the communicating frequency (Smith,
The individual hairs also exhibit similar properties as antennae for the reasons
stated above. However, as illustrated in Figures 2-1h,i, 2-2a, and 2-3b,c, the hairs are not
all of the same length, but taper gradually so that they closely resemble a man-made log-
periodic antennae as shown in Figure 2-4. These antennae are receptive to a general
range within the confines of their respective lengths. These man-made log-periodic
antennae were the antennae of choice in the 1960's and 1970's, and were positioned on the
roofs of houses for improving television reception. The metal rods of these antennae
were receptive to wavelengths over a broad range and tapered much like the moth's
antennae. Man has since improved upon this now "primitive" practice and uses the radar
dish, or "satellite dish" as it is often referred to.
Figure 2-4. Man-made log-periodic dipole array.
The radar dish type of antenna is based on a single detector at the focus of a
reflecting dish. The reflecting dish only reflects incoming radiation to the central detector
and does not receive the radiation directly. The distance between the dish and the
receiver influences the receiving frequencies. Many man-made antennae are constructed
with a central receiver surrounded by reflectors or "modifiers" that serve to enhance the
antennal properties of the central receiver. The modifiers do this by altering the radiation
pattern (The ARRL Antenna Book, 1974) of the central antenna, and are most effective
relatively close to this centralized receiver. Figure 2-5d shows a sensillum coeloconica
on a grasshopper. This particular form has a central receiver surrounded by a resonant
cavity. All sensilla coeloconica have a make-up similar to that briefly mentioned in the
paragraph above. Usually they constitute a central peg surrounded by six or more
inwardly slanted structures. On the red-banded leaf roller moth about 14 can be counted
while on the tiny green peach aphid, an incredible 30 or so can be seen (Callahan, 1975b).
A similar configuration is shown in Figures 2-5e,f, the difference being the number of
"central" receivers within the resonant cavity. Figure 2-5e is a redrawing of the infrared
receptor of Melanophila acuminata. The sides of the pit containing the sensory organs
are lined with exocuticle (Evans, 1966b) which is highly reflective to light (Callahan,
1990). The sensory organs are, as one might anticipate, not covered with exocuticle
(Evans, 1966b) since that might defeat its purpose of sensory perception. These sensory
organs are approximately 15 pm long, which is in the infrared range. Still another
example is the interommatidial hair of the corn earworm which finds itself surrounded at
Figure 2-5. Diagrammatic
reflector antennae: (a) man-
made satellite dish; (b) insect
overhead view and (c) lateral
view; (d) insect coeloconica,
Orthoptera: Locusta; (e)
infrared receptor, Coleoptera:
Melanophila; (f) insect
the base by small stub-like projections (Hsiao and Siisskind, 1970). The difference is
that, in this configuration, the modifiers are much smaller than the central peg.
There are, additionally, two good examples of man-made antennae that find
analogies in insect sensilla. These are the car antennae and the "rabbit-ear" antennae of
The radio antenna found on many cars consists of an elongated metal rod with a
spherical metal cap at the end tip. The purpose of this tiny sphere is, in part, to minimize
impedance of the incoming radio wave with the antennae. A square or similarly highly
angular shape would not work as efficiently. The fact that many insects do indeed
possess this characteristic, even across many unrelated taxa, suggests a common purpose.
Is this similarity man-made antennae have to insect sensilla a coincidence?
I will ask the reader to refer to Figs. 2-lc and 2-1 f and notice the enlargement of
the antennal segments as they reach the tip. Two more drawings depict the same
phenomenon (Figs. 2-ld,e). Even the lamellate antenna shown in Fig. 2-6 exhibits a form
of capitate antennae. Scarab beetles are the only representatives with lamellate antennae
and amazingly, all of them have it (it is the distinguishing characteristic).
There are two ways to minimize impedance to an incoming EM wave, the first is
by a circular tip (already mentioned) and the second is by tapering the tip. I have often
noticed that many scarabs have the three terminal segments of the antennae closed as in
Figure 2-6a. The tip will be slightly pointed and round. However, when they bring their
antennae out from under their body in order to test the air, the three segments open up as
Figure 2-6. Lamellate antennae (Coleoptera: Scarabaeidae) (a) closed; (b) open.
displayed in Figure 2-6b, in fact I have witnessed them opening these terminal segments
even wider than the figure portrays.
By performing this action, the beetle has slightly altered the properties of its
antenna, at least in terms of electromagnetic reception. There are now three potential
receiving sites that are each different from the original tip because of its change in form
(a change in form of an antenna always brings about a change in the EM properties of the
antenna). An argument can be made that by separating these three terminal segments, the
surface area is increased for diffusion of airborne molecules, and that this is the real
reason for this behavior. However, if surface area were important to the scarab beetle,
they (or at least some) would have the entire antenna shaped like the terminal three
segments, and the antenna would then be termed pectinatee' (Fig. 2-1h). Since this is not
the case, one must assume that scarab beetles have this type of antenna for a very, very,
good reason. Researchers have already suggested that the lamellate organs on some
beetles may be infrared receptors (Corbiere-Tichane, 1971, 1974; Corbi&re-Tichane and
The rabbit-ear type of antenna was used for television reception inside the home
before cable moved in and erased the need. These antennae are characterized by two rods
that can be separated from one another in varying degrees to optimize reception. Once
establishing this critical distance, the individual may then revolve the entire apparatus in
an effort to increase the quality of reception even further.
Insects also have two antennae composed of two largely hollow rods (Chapman,
1982). They often separate them from one another while apparently scanning the
environment. I have often observed insects rotating their own antennae while scanning
the environment and simultaneously rotating their entire body. These motions by insects
closely resemble the motions taken by a desperate football fan of the past on Sunday
afternoon, trying mightily to tune into the "big game".
In this section of the review, I would like to discuss some of the similarities and
differences of antennal morphology across insect taxa.
Depending upon where you begin your analysis, your comparison could be highly
biased. For example, after examining all butterfly species, one may conclude that there is
a high degree of consistency since all butterflies are characterized by their knobbed
capitatee) antennae. But their close relatives the moths, exhibit pectinate, bipectinate. or
filiform antennae. The fact that moths are largely nocturnal is not a valid argument for
the difference in antennal shape since a well-known diurnal moth, Ctenucha virginicu,
has pectinate antennae identical to those of its moth relatives.
Similarly, all the true bugs (Hemiptera) have 4 or 5 segmented filiform antennae,
but huge variation exists within beetle species (Order Coleoptera). Even though most
beetles have either filiform or capitate antennae, all scarab beetles have their own unique
form as discussed previously. Ptilodactylids and Pyrochroids (Fig. 2-lh) are both
recognized for their unusual-looking antennae which in the latter can be pectinate, serrate,
or even plumose in some males.
This last point brings up another difficulty in trying to make sense of antennae, for
some beetle species exhibit sexually dimorphic antennal morphology. This is also true of
the mosquitoes and midges (Order Diptera) in which the males possess highly plumose
antennae but those of the females are relatively reduced. Because both males and females
inhabit similar niches one may hypothesize that the antennae for these dimorphic taxa are
not modified for the environment but may exhibit modifications designed more for
courtship purposes. Indeed, this is suspected to be the case in mosquitoes, where the
male possesses plumose antennae designed to tune in to the wingbeat frequency of the
female (Fig. 2-li) (Boo and Richards, 1975).
If one views the antennae of Cerambycid beetles as potential detectors of EMI
radiation, then the antenna length should be proportional to the wavelength received, or a
multiple of the wavelength. Because the antennae are so long (several centimeters or
longer) the wavelengths received must be in the microwave region. The sensilla on the
antennae would be expected to respond to wavelengths corresponding to their own
dimensions, that is, in the infrared and at the 'third level' as discussed earlier and
displayed in Figure 2-2. However, the antennae proper would be poor detectors of
infrared energy due to their size, and so they must be responsive to longer wavelengths.
The uncharacteristic length of the antennae in Cerambycids appears unwieldy and
a hindrance to movement. Therefore, we must assume that these extremely long antennae
are in some way necessary for survival since they have been retained in the lineage for so
Insect Sensilla. an Overview
Insects have a wide diversity of sensilla located on their body, legs, wings, and
most especially, their antennae. Much like my former discussion, prevailing belief
among entomologists maintains that these sensilla somehow capture airborne molecules.
Chemosensing in insect cuticular sensilla is thought to include:
a) trapping stimulus molecules from solution or air;
b) conducting the molecules through the cuticle to the site of recognition;
c) stimulus recognition with membrane depolarization (generator potential); and
d) generation and conduction of nerve impulses (Zacharuk, 1980).
Chemical recognition in insect sensilla is "assumed" to take place on the plasma
membrane of the dendritic terminations.
Common sense dictates some other function as well. since over 400 different
shapes and sizes of sensilla exist (Callahan, 1975a). How do these different shapes and
sizes enable the sensilla to trap airborne molecules?
If sensilla shapes do not indicate resonance then exactly what is their
function? One cannot isolate them from the system, ignore form and
explain all of olfaction by analyzing nerve impulses at the base of the
sensilla as is presently done. Nor do nerve impulses recorded from
sensilla bombarded with scent explain how the energy from the scent
couples to the sensilla, yet to this very day the function of the kinds of
shapes of the sensilla are totally ignored... (Callahan, 1990, p. 244)
This incredible diversity in sensillar shape has inspired researchers to categorize
insect sensilla. Because the following categorization is relatively recent, I will adopt the
system by Zacharuk and Shields (1991) who listed ten categories.
1. sensilla chaetica- heavy, thick-walled bristles or spines that are aporous or
2. sensilla trichodea- hairs that may be aporous, uniporous, or multiporous
3. sensilla basiconica- peg-like
4. sensilla coeloconica- pegs set in shallow pits. usu. aporous, multiporous
5. sensilla ampullacea- pegs in deep pits
6. sensilla campaniformia- aporous domes within multiporous cuticle
7. sensilla placodea- plates level with the cuticular surface, usu. uniporous,
8. sensilla styloconica- pegs set on an elongated style. mostly uniporous, occas.
9. sensilla scolopalia- subcuticular
10 sensilla squamiformia- scale-like (not found in immatures)
Other sensilla are considered to be variants of these ten basic types, or may even
represent a composite. For example, many sensilla trichodea are terraced or possess
vertical or helical striations on their exterior. They may also bend or curve toward the tip.
Sensilla can also be categorized by virtue of their electrophysiological function
into mechanoreceptors, chemoreceptors, or photoreceptors. It should be emphasized that
neither the modality nor the specificity of a hair type can be predicted from its appearance
under the light microscope (Hansen, 1978), however, some generalizations can be made
and do help to simplify an otherwise difficult issue.
"Mechanoreception is the perception of mechanical distortion of the body caused
by the external stimuli of touch and air- or water-borne vibration, or due to the internal
forces generated by activities of the muscles." (Mclver, 1975). Mechanoreceptors consist
of one or two dendrites that innervate the base of the sensillum (Thurm, 1964).
Chemoreceptors are characterized by their response to olfactory stimulation, and
morphologically as sensilla with multiple dendritic innervations. If they are thick-walled
and possess a single opening at the tip they are considered to be gustatory chemoreceptors
(Dethier, 1963; Slifer, 1970); if thinner-walled, and possessing multiple pores then they
are considered to be olfactory chemoreceptors (Slifer, 1970; Zacharuk. 1980). Usually
the sensillar tip has a terminal pore with a dendrite directly beneath it. However, some
sensilla do not have that terminal pore seemingly disqualifying them as contact
chemoreceptors except that a dendrite is still encountered less than one micron below the
tip. A mechanoreceptor has no terminal pore, or any pores in its cuticle, but the dendrite
terminates at the base of the sensillum and does not extend to the tip.
Behaviorally, this classification may not stand up either, since a contact
chemoreceptor discovered by Stadler and Hanson in 1975 was found to have "olfactory"
capabilities. Similarly, the efficiency of the grooved-peg sensillum on Aedes aegypti as
an olfactory receptor does not appear to be affected by the fact that is has only a single
terminal pore (Davis, 1988). Stidler and Hanson (1975) have commented that this
convenient separation of all chemoreceptive sensilla into one of two groups does not
always apply. They cited behavioral support from Slifer (1970) and the physiological
study of Dethier (1972) along with their own electrophysiological results. In addition, the
presence of both contact and olfactory sensilla on the same organs (Dethier and Kuch,
1971) means their location can not be a criterion for classification either. If this
classification scheme is not very reliable, then its use should be curtailed.
The difference between mechanoreceptors and chemoreceptors is often inferred
from their internal morphology and may be just as difficult to separate reliably. Often, an
individual sensillum exhibits a dual function, that is, both mechano- and chemoreceptive
functions. These chemo-mechanosensory sensilla were positively identified on ticks
(Foelix and Axtell, 1971; Foelix and Chu-Wang. 1972; Chu-Wang and Axtell, 1973) as
well as beetles (White and L uke. 1986) and moths (Callahan, 1968) and are discussed in a
review article by Zacharuk in 1985.
White and Luke (1986) found that non-porous hairs that tapered to a fine point
were the most common type on the antennae of a beetle, Oryzaephilus surinamensis.
Since these sensilla are the most common, and they have no pores, just how is the
receiving molecule internalized by the antennal sensilla for eventual detection by
dendrites if chemosensory function is supposed? Additionally, some sensilla with a slit
opening had an innervated dendrite just below the slit, while others did not. Because
detection of molecules is thought to be dependent upon dendritic stimulation by the
airborne molecule, why were there no dendrites underneath some of these openings/slits?
Diffusion would take far too long to pass down the entire length of the sensillum If the
sensilla does not allow molecules to pass through its impermeable cuticle, then what
indeed is its function? Why are these pores found in so many different shapes and sizes
as represented in the insect world? Three differently shaped porous sensilla were even
found to exist on a single insect, Cimex lectularis (Steinbrecht and Miller, 1976) Could
all of this be simply attributed to random variation, or could there be an underlying
Some of these tapered hairs became abruptly blunt and occasionally swollen at the
tip just as a clubbed antenna or a capitate antenna would be. No hypotheses in the
literature have been found speculating how this morphological adaptation increased the
capture rate or ability to capture an airborne molecule. Pilgrim (1991 a) reflected on this
phenomena while admiring these sensilla on flea larvae when he asserted that "...at least
those with swollen tips must have a functional significance" (italics mine).
Insect antennae are generally considered to he chemoreceptive organs consisting
of a plethora of chemoreceptors. Why then is it that 68% of the antennal sensilla of O.
surinamensis are mechanoreceptors (White and Luke, 1986)?
Clearly, many incongruities exist within the present classification scheme. At
least 400 different types of sensilla (Callahan, 1975a) exist on insects and contemporary
entomologists contort this variety into only three functional types. Is it even remotely
possible that various insect sensilla are resonators for electromagnetic frequencies as
several researchers have suggested over the years (Grant. 1948; Miles and Beck, 1949;
Laithwaite, 1960; Callahan, 1967)? To investigate this possibility further, I will first
discuss some of the basic properties of an antenna, insofar as they relate to insects.
A dielectric waveguide is a type of antenna. However, it differs from a traditional
antenna primarily in the material of which it is composed. Traditional antennae are made
of a conducting substance, such as metal, but dielectric antennae are not. They may be
composed of almost any material that is a poor conductor.
The prefix 'di' means 'two' and refers to the two electric charges found on
opposite sides of the non-conducting material. The reason for this charge separation is
due to the dielectric material, which because it is a non-conductor, prevents the
dissipation of charge to cross from one side to the other. Generally, the adjacent sides
contain opposite charges, one positive, the other negative (Athenstaedt and Claussen,
Fortunately, the two antennae types have similar functions, which will make this
section easier for the reader to follow. Basically, a given wavelength or frequency can be
received by both types of antennae. In some instances, however, one antenna will have
an advantage over the other, but both will work under most conditions. For this reason, I
will first review selected properties of a standard antenna, and will then follow with basic
dielectric waveguide theory, and then finally I will conclude with the striking similarities
that are found between dielectric waveguides and insect sensilla.
Exact theories for antennas are not usually available or even understandable
because of the complex equations and higher level calculus that is involved in predicting
their properties. Therefore, antenna research began empirically with the construction of
various materials into many different shapes and sizes in order to determine
experimentally what worked and what did not. The first man-made electromagnetic
antenna was developed by Hertz in 1887 and was, quite simply, a circular loop of wire.
The results obtained from this and subsequent studies have revealed four fundamental
properties of all antennas. In order to help me recall these properties, I have labeled them
with the acronym "G.R.I.P." They are gain, radiation pattern, impedance, and
The gain of an antenna is the ratio of the maximum radiation intensity to the
maximum from a reference antenna with the same power. Measurement of gain is
accomplished by direct comparison with a calibrated standard-gain antenna which is
specifically designed for a particular frequency (The ARRL Antenna Book, 1974).
Therefore. a given antenna with an established gain will be found to have its gain altered
when different frequencies are tested. Gain in one direction is always obtained at the
expense of gain in other directions. High gain in the direction of the signal both lessens
the requirement for later amplification and reduces the noise picked up in directions from
which signal does not arrive. Gain is closely related to the directivity2 of an antenna and
books will often use these terms synonymously3, a usage I will adopt for this paper.
The radiation pattern of an antenna determines the spatial distribution of these
radiation intensities. It refers not only to the maximum radiation intensity, usually in the
form of a lobe, but also to all secondary lobes (Figure 2-7). Determining the radiation
pattern is important because large secondary lobes decrease the gain of the antenna, and
knowing they exist in a given pattern allows for various adjustments to be made so that
reception is optimized. The two main features of a highly directive radiation pattern, and
therefore a highly directive antenna, are narrow beamwidths4 and small sidelobe levels
2All antennas exhibit directivity because the intensity of radiation is not the same
in all directions.
3Directivity is based solely on the shape of the directive pattern, but gain takes
into account power losses which adjust the lobe pattern.
4Beamwidth of a directive antenna is the width, in degrees, of the major lobe
between the two directions at which the relative radiated power is equal to one half its
value at the peak of the lobe.
Figure 2-7. Three types of directive radiation patterns for hypothetical antennas. a)
directive pattern with main lobe and two secondary (2 ) lobes; b) highly directive
radiation pattern with reduced 2 lobes; c) directive radiation pattern with
disruptive 2 lobes
Impedance is the property which allows for the incoming frequency to be detected
from the atmosphere without loss. This property is presented by the antenna at its
terminals, and provides a smooth transition and a certain degree of matching with the
Polarization is usually defined in terms of the orientation of the radiated electric
field "E" in the direction of maximum radiation (i.e. a vertical wire antenna is vertically
polarized). Antenna polarization is generally elliptical. One final characteristic of
antennas is given its own theorem. This is known as the Reciprocity theorem, which
states that the properties of antennae (G.R.I.P.) are the same for both transmitting and
receiving. Therefore, if insect sensilla are antennae, their intrinsic ability to send
electromagnetic signals is equivalent to their ability to receive signals from the
environment. This fact has enormous implications for intraspecific as well as
interspecific communication among insects, most especially among social insects (i.e.
ants, bees, and termites).
Antennae are a vital part of many communication and radar systems, and are
usually an important topic in final year undergraduate courses and M.Sc. courses in
electronic engineering. They are the basic components of any electronic system which
depends upon free space as a propagation medium. Antenna dimensions can vary from
very small fractions of a wavelength to many wavelengths. This suggests, correctly, that
antennas assume very different sizes for different frequency bands. Long-wire antennas
are simple both electrically and mechanically, and there are no critical dimensions or
adjustments possible. As the wire becomes gradually longer, the width of the main
radiation lobe decreases, thus improving the gain and the overall antenna efficiency. For
example, the lobe size for a particular antenna at a given wavelength (1) was 900 while
a similar antenna eight wavelengths long (81) displayed a main lobe of only 30.
For directional antennae, it is desirable to have a narrow beam width and for the
radiation to be projected forward in one direction. Although the forward mass of
radiation is the main lobe, antennae often exhibit side lobes as well. These side lobes
decrease the gain of the antenna, and therefore need to be controlled if possible.
Antennae designed for navigation usually have a narrow beam width, and the
radiation is projected forward in one direction A radar system usually requires a high
gain antenna which can be steered to scan over a particular area. Thick-walled antennae
work well over relatively wide bands of frequency, while thinner-walled antennae are
rather sharp in tuning.
Other antennae need not be directive but only of the appropriate length. I have
already mentioned submarines utilizing antennae of appropriate length but airplanes must
deal with this problem as well. Aircraft take the length of the plane into account in order
to "lengthen" their antennas so as to properly tune in to the correct wavelengths from the
ground. Electrically small antennas (length << .) have a very poor radiation efficiency.
This is a basic limitation of electrically small antennas. Optimized antennae can be
absolutely small, but not relatively small. One exception to this rule concerns infrared
detectors which reportedly improve as the devices are made smaller than the receiving
wavelength (Hu and Richards, 1989; Peatman and Crowe, 1990).
Coupling and Arrays
When two similar antennae are brought within a certain critical distance of one
another, coupling is said to occur. This is no more than interference of the radiation
patterns so that a new form is created. More often than not, constructive interference may
occur such that the field strength may exceed the field produced by the same power in a
Linear arrays consist of three or more antennal elements lined up such that all are
contributing to form one unique radiation pattern. Generally speaking, the linear array is
more directive than any of its elements alone, so that it dominates properties such as main
beamwidth and sidelobe levels; in fact, the radiation pattern of the element is practically
lost to the radiation pattern of the array. Assuming no coupling in an array (equidistant
elements), the main beamwidth is governed by the complete array length. Certain
combinations of antennal elements result in very specific directive patterns. The gain and
directivity that can be secured by intentionally combining antenna elements into an array
represent a worthwhile improvement both in transmitting and receiving.
Two varieties of linear array include the end-fire array and the broadside array.
The principal direction of radiation for an end-fire array is parallel to the axis of the array
and to the plane containing the elements while the broadside array has its principal
radiation perpendicular to the axis of the array. It is characteristic of broadside arrays that
the power gain is proportional to the length of the array but is substantially independent
of the number of elements used, provided the optimum element spacing is not exceeded.
Both broadside and end-fire arrays can be readily combined to increase gain and
directivity and this is in fact usually done when more than two elements are used in an
array. The combinations that can be built are practically endless.
A phenomenon related to coupling is a parasitic array. This differs from true
coupling in that one antenna is not powered via external sources. This parasitic element
has no power associated with it except for the power it picks up solely from its close
proximity to the power element containing the current, known as the "driven element".
Parasitic elements not only have their own radiation pattern altered, but they also affect
the radiation pattern of the driven element. The actual impedance of an antenna element,
becomes the sum of its self-impedance (with no other antennas present) and its mutual
impedance with all other antennas in the vicinity. Although the calculation of mutual
impedance between antennas is difficult, model antennas show that adding parasitic
directors and/or reflectors often increases gain for specific frequencies.
A special type of parasitic array involves parasitic elements acting as directors or
reflectors. The driven element is centrally located and is surrounded by parasitic
elements that may act either as a director or a reflector depending upon their size and/or
location relative to the driven element as well as the phasing of the currentss. This
situation is analogous to the sensillum coeloconica of Fig. 2-5c.
Reflector arrays may also take the form of a dish, such as the radar dishes many of
us use to pick up satellite transmissions for television broadcasts (Fig. 2-5a). Because
reflector antennae are highly directive, they are often revolved in order to receive signals
from all directions. Other antennal arrays are modified to receive from all directions but
have no directionality (radiation lobes extend out in all directions). This situation is
analogous to the sensilla coeloconica represented by Fig. 2-5d.
Since associations into groups, communities, populations, and biocenoses exhibit
their own specific features due to "coalition", an aggregate of elements can jointly do
things which each of them separately could never achieve (Presman, 1970). The
individual units, whether they be of a conducting nature or a dielectric nature, also have
their bearing on how an antenna array will function. In insects, sensilla arrays are the
norm, not the exception, and are indicative of multiplicative signal processing dielectric
As I have already mentioned in the introduction, dielectric aerials employ a
system of dielectric elements, as distinct from a system of conductors, to either radiate or
collect electromagnetic energy from one or more directions. The very general properties
for antennas mentioned above also apply for dielectric antennae. Because insects are not
composed of metal, their antennae are not likely conducting but are probably dielectric.
Therefore, some characteristics of dielectrics are discussed below in order to help clarify
their role in sensory perception.
The transmission of sinusoidal electromagnetic waves in waveguides was first
investigated by Tyndall in the 1860's (Tyndall, 1866) and later developed by Rayleigh in
1897. Although investigators continued to study dielectric waveguides throughout the
early part of this century, their practical importance was not realized until some 30 years
later (Barrow, 1936; Carson et al., 1936; Schelkunoff. 1937; Chu and Barrow, 1938) and
they were first used by the Germans in World War II (Callahan, 1989). The three main
types of dielectric aerials include 1) a solid dielectric rod, 2) a hollow dielectric tube, and
3) a dielectric horn. Only the first two will be discussed at any length.
These three radiators may all be excited by conventional methods and they all
have the common property that they produce single lobe radiation patterns directed along
the axis of the aerials. Their directivity is proportional to their length, which is the most
distinctive characteristic of the family. Additionally, the efficiency of dielectric
waveguides is such that energy loss from a wave to the waveguide is zero; mathematical
and experimental verification of efficient dielectric waveguide systems is well
documented (Weinstein, 1969).
Generally speaking, a correctly designed dielectric tube antenna is more directive
than a dielectric rod of the same length. Most insect sensilla are not solid cuticle
throughout, but instead are tubular. Additional factors that modify an antenna's
efficiency include taper, diameter, thickness, dielectric constant, length, and its presence
within an array.
Gradually tapering the antenna as well as decreasing the diameter may both
severely reduce the side lobes, thus increasing the main lobe and the antenna's gain
(Mueller, 1952). increasing the taper by only a small margin, say from 20 to 4, was
enough to decrease the side lobes noticeably (Callahan, 1985.) Tapering the rod provides
impedance matching to free space and minimizes reflection at the end of the rod, thereby
producing a field distribution along the length of the rod that results in smaller side lobes.
Gradual tapering along the entire length provides for better impedance matching than a
more abrupt taper.
The thickness of the antenna is also very important, but optimization is difficult to
achieve. The thinner the dielectric tube, the greater the power. However, a very thin
antenna will have structural problems or will at least break easily. The only known
compromise has been to perforate the antenna with extremely fine pores (Mosely et al.,
1964). This simulates an infinitely thin wall, while at the same time does not sacrifice
structural integrity. Arthropod chemoreceptors are characterized by their thin walls and
very fine pores (Slifer, 1970; Zacharuk, 1980) that can only be seen with the aid of a
scanning electron microscope (Foelix and Chu-Wang, 1973). It is entirely possible that
the presence of fine pores in a particular sensillum, may exist in order to increase the
power of the "antenna", more so than their purported function as simple "windows" for
allowing the passage of molecules through an otherwise impermeable cuticle.
In a dielectric antenna, the dielectric constant helps to determine the resonant
wavelength of the antenna. Dielectric rod aerials have been made with polystyrene which
has a dielectric constant of 2.5. If materials of higher dielectric constant are used, the
diameter of the rod must be reduced to give similar performance.
The use of longer dielectric rods helps to systematically reduce the width of the
main radiation lobe by a factor of two or more. For example, when the length of a
dielectric rod was increased from 2k, to 4X, to 61, and finally to 8X, the beamwidth
decreased from 57, to 400, to 300, and finally 25", respectively (Kiely, 1953).
Beamwidths narrower than about 200 cannot be achieved with a single dielectric rod, and
it is necessary to use arrays of rods to obtain narrower beams and to enhance
performance. Another experiment involving four dielectric rods spaced 3/2 X apart
produced a beamwidth of only 100. Arrays of two and four dielectric rods were used
extensively in Germany during World War II as radar aerials and as search aerials for
detecting allied radar transmissions. A large rectangular array of 42 dielectric rods was
designed in the United States at Bell Telephone Laboratories and was used by the
American Navy for gunnery fire control purposes (reported in Kiely, 1953).
The properties of biological dielectrics have been discussed by Schwan (1957),
Grant and co-workers (1978), Pethig (1979), and Hasted (1973), among others.
Unfortunately, none of them investigated the dielectric properties of insect cuticle.
Insect Sensilla and Radiation Detection
Charles Valentine Riley, former chief of the Entomological Commission and
author of Insect Life (1889-1894) suggested that insects might sense subtle vibrations to
which we are blind (Riley, 1894). Jean Henri Fabre (1913) was the next to publish his
thoughts that perhaps moths are tuned to certain electromagnetic frequencies, while
Eugene Marais (1937) speculated that termites might do the same. Electromagnetic
frequencies are, of course, picked up by appropriately structured antennae, but no one
looked for them on insects until 1948 when Grant, an electrical engineer, was the first to
publish a paper indicating a possible detector for this EM radiation by pointing out that
certain pit sensilla on insects closely resembled dielectric waveguides and resonators
already developed by man (Grant, 1948). One year later, Miles and Beck (1949)
hypothesized that certain olfactory receptors are indeed radiation receptors, based upon
their experiments with honeybees and the bees' attraction toward an enclosed box
containing honey. This box was equipped with an infrared transparent window. Duane
and Tyler (1950) hypothesized that the infrared radiation arising from the body heat of
the female moth could be the signal that attracts the male. Laithwaite reopened the
subject again in 1960 when he discussed the assembling of moths due to radiation and
agreed with Grant by noting the similarity of insect antennae to certain radar antennae
designed by man. None of these researchers, however, continued to publish on this
Phil Callahan developed the hypothesis in the 1960's when intensive research
began in his laboratory (Callahan, 1965a,b,c,d, 1967, 1968, 1969). Support for this
hypothesis came from Griffith and Siisskind (1970) who by creating models discovered
that insect sensilla trichodea could very well be working dielectric antennae. Hsiao and
Siisskind (1970). Hsiao (1972), and Griffith (1968). suggested that the optimal operating
setal length for a dielectric antenna was 6 wavelengths and they all found support for this
theory in various forms. Evans (1966b) investigated infrared receptors and infrared
radiation from sensory pits on a beetle as Grant (1948) had first pointed out. Okress
(1965) added theoretical support for the dielectric waveguide theory for insects, while in
a personal communication to Callahan pointed out that dielectric theory was more
suitable than conductive theory (reported in Callahan, 1981). Eldumiati and Levengood
(1971) made the observation that the moth's major antennal spines are hollow thin-walled
tubes with a tapered cross section. They too concluded that this structure would be
suitable as a dielectric antennae.
Many insect sensilla are elongated spines or hairs called sensilla trichodea
(meaning hair sensors). These sensilla are not localized to a body region but can be
found on e% er\ region of some part of some insect's cuticle. They all taper gradually to
the tip, which is often quite pointed and which provides very good impedance matching
with the atmosphere. The sensilla have very thin walls, much thinner than that found
covering the body proper (an excellent picture can be found in Figure 1 from Zacharuk et
al., 1977) and of a fixed consistency throughout, resulting in a uniformly sclerotized
spine (Richards, 1952). Often these spines are perforated with tiny pores, which
electrically reduces the thickness of the cuticle' by reducing the dielectric constant and
increasing antenna gain, as mentioned earlier. The length of most of these sensilla
trichodea are less than a millimeter, which places their optimal frequencies for
electromagnetic detection in the infrared range (Callahan, 1965a) or the microwave range
(Callahan et al., 1968). Eldumiati and Levengood (1971) suggested that longer
wavelengths may be detected if the main trunk is considered as a waveguide.
Based upon the lengths of some sharply tapering spines occurring on the scape
and pedicel of several species of noctuid and saturniid moths, these spines may be tuned
to the visible region of the spectrum (Callahan et al., 1968). Electrophysiological
responses have shown these spines to respond to frequencies across the entire visible
spectrum (Callahan, 1968). A correlation between length of sensillar hairs (trichobothria)
and frequency perceived was found by Gorner and Andrews (1969) and Drasler (1973).
These articles show that different antennal lengths are differentially tuned to various
frequencies regardless of whether it be a man-made antenna or an insect antenna.
Since infrared radiation falls between the visible and radio regions of the
spectrum, infrared demonstrates many of the characteristics of both. It may be focused
by lenses and yet can be transmitted like radar or radio through materials that block
visible light. Emphasis is added to this comparison by the use in infrared technology of
both optics (refraction and reflection) and radio waveguidee and resonant cavities)
techniques to detect such radiation (Valli and Callahan, 1968). The fact that infrared
radiation may behave like both can be revealed theoretically and by direct measurements
obtained through the making of antenna models. Some unique properties of infrared
antennas have been revealed by Hu and Richards in 1989 and Peatman and Crowe in
1990. These two groups found the performance of many types of infrared detectors
improve as the devices are made smaller (<< wavelength).
Model insect dielectric antennae were designed and investigated by Callahan
(1991) who found that the longer and thinner the sensillum type. the more directional was
the associated radiation pattern. Conversely, the shorter, stubbier insect sensilla,
corresponding to sensilla chaetica and sensilla basiconica, displayed a broader beam
width and therefore a loss in gain. Trichodeae which are curved also have a radiation
pattern which reflects this, such that a trichodea curved to the left side will have its major
lobe curved to the left as well.
Corrugating a sensillum basiconica increases beamwidth until it is almost totally
nondirectional. These sensilla have been found on many insect antenna as well as on the
hind legs of mosquitoes. Similar corrugations have been found on the blowfly (Dethier,
1972), the bed bug (Steinbrecht and Miller, 1976). the cerci of a cricket (Schmidt and
Gnatzy, 1972). On the sensilla trichodea of honey bee antennae (Dietz and Humphreys,
1971) they appear under the scanning electron micrograph (SEM) as ridges spiraling up
the sensilla, barber-shop style. Additionally, the bed bug (Steinbrecht and Miiller, 1976)
and many other insects have both smooth and ridged sensilla, thus showing that the
differences are not species-related.
Wavelengths in the microwave-infrared-visible range cannot penetrate the cuticle
to a significant degree (Presman, 1970; Konig, 1989). The shorter the wavelength the
more easily it is absorbed by matter. This means that if electromagnetic bioinformation is
to be transmitted between living beings, both the signal source and the receiving site
(receptor) must be placed on the surface of the body (Kiinig, 1989). The only sensory
structures on the outer surface of insects are the sensilla as well as the legs and antennae
proper. It seems natural that the insect sensilla would have this purpose of directing and
collecting the electromagnetic radiation since this function has already been established
for very similar surface structures on the compound eye of insects.
There are protuberances on the insect cornea that Bernhard and Miller (1962)
have called "corneal nipples". These nipples are arranged in a perfect hexagonal array,
and this degree of precision strongly points to a very specific function. After making
measurements on scaled dielectric models and based upon spectrophotometric analysis on
insect corneas, they concluded that this corneal nipple array acts as an impedance
transformer which matches the characteristic impedance (inverse of refractive index) of
air to that of the lens material over a broad wavelength range (Bernhard et al., 1965).
These results were confirmed by the application of a mathematical model.
The insect exoskeleton is composed of a very rigid cuticle known as chitin.
Hardened or stiff antennae with good solid walls make better antennae than those with
flimsy, pliable walls. The waxy layer covering the insect cuticle also has its role. The
waxy layer has a dielectric constant between 2.5 and 3 (Cailahan, 1967), which is similar
to the dielectric constant of polystyrene, an excellent dielectric. Both Griffith (1968) and
Shackelford (1970) also determined that the insect exoskeleton and insect waxes are
excellent dielectrics with the proper dielectric constant for a dielectric antenna, thus
adding their support to Callahan's hypothesis.
Many biological epithelia are provided with a waxy protective layer which
apparently developed as a necessary prerequisite for an organism moving from an aquatic
to a terrestrial existence. The wax layer can also have the structure of a permanent
electrical dipole conforming to the physical laws of an electret (Warnke, 1989a). An
electret is any insulator containing a stored charge (Mankin. 1976). Electrets can be
formed by different methods, such as in the presence of heat or an electric field. Liquid
beeswax exposed to an electric field will also harden into an electret (Jaeger, 1934) as
does carnauba wax when exposed to a magnetic field (Bhatnagar, 1964). A drop of
purified beeswax, filtered through filter paper, and diluted with benzene, still did not form
an even layer when applied to a flat plate (Mankin, 1976), whereas the wax layer
apparently forms an even coating on each spine of an insect from molt to molt.
Piezoelectric and Pyroelectric Properties of Insect Cuticle
The ability of any insect to detect external stimuli is largely dependent on the
properties of its cuticle. I have already mentioned the sensilla and the evidence
supporting their possible function as working electromagnetic antennae. However, not all
antennae are passive detectors of electromagnetic frequencies. Usually, their primary
function is to "...pick up (lock into), amplify, and in the case of arrays, analyze a signal."
(Cailahan, 1973). This brings us to a very important question; what is the detector or at
what level does detection take place?
Beament (1961) measured a potential difference of 2 x 104 V/cm across the
cockroach integument. The resistance found across the insect cuticle was measured at
108 Q by French (1988). Measurements with both living and dead flies demonstrated
voltages between parts of the body (Becker and Speck, 1964). The voltage source was
hypothesized as originating from a galvanic element which consists of the protein of the
body and the cuticula. This "body battery" as Becker and Speck named it, could be
switched off by complete drying only to set in once again when moistened (Becker and
The very high resistance found across the insect's cuticle helps to explain the
dielectric properties of the cuticle, whereby a very effective charge separation can be
maintained. This property of the cuticle also confers upon it a certain degree of
mechanical stress, extremely sensitive to impinging vibrations. Piezoelectricity is the
property of a substance such that it converts pressure to electricity or electric polarity.
Pyroelectricity has a similar definition but substitutes heat for pressure. Any structure
with piezoelectric activity also has pyroelectric activity (Warnke. 1989a). For most
dielectric materials, the polarization disappears when the field is removed. In some
crystals such as triglycine sulfate (TGS), however, a strong residual polarization remains.
The residual polarization of pyroelectrics is strongly sensitive to minute changes in
temperature. If temperature is varied, even in the slightest degree, the consequent change
in residual polarization causes a new charge to appear across the dielectric. The charge
will be positive or n.il'al i e depending on the direction of the temperature change
(Callahan and Lee, 1974).
Piezoelectric properties of the insect cuticle were first reported by Callahan
(1967). He found that the exoskeleton produced both sound and radio waves when
stressed. That same year Morris and Kittleman (1967) found piezoelectric activity in the
otoliths of some species of bony fishes, where it is believed to be involved in sensory
perception. Six years later, Strickler and Bal (1973) suggested that the microtubules may
connect the sensory neurons with the moving tip of the hair (sensilla) and function as a
piezoelectric crystal. The topic developed nicely with the work of Zilberstein,
Athenstaedt and colleagues who measured both piezoelectric and pyroelectric (PZE and
PE) properties of the cuticle not only of insects, but some other arthropods as well.
It was discovered that PE and PZE responses will not only occur in live insects
(Simhony and Athensteadt, 1980) but will also be measurable in dead, dry integument
preparations as long as the polar tissue texture remains intact (Athenstaedt and Claussen,
1981). Although it is true that the PE and PZE voltage responses of the integument of
live animals were considerably higher than those of the same animals after death, the post
mortem responses declined steadily for about three hours (without changing the position
of the specimen) and then remained constant over a period of months (Athenstaedt and
Claussen, 1981). Athenstaedt (1972) found that PE and PZE properties were found to
exist in the integument.of beetles that have been kept in zoological museums for more
than ten years The natural conclusion to be drawn is that the established PE and PZE
effects are due to a physical "material property" of the integument and that they are not
caused by ionic transport or other bioelectrical phenomena normally associated with the
living state (Athenstaedt and Claussen, 1981) However. since these properties can be
enhanced by the living state, it might be that the insect augments this property for
heightened sensory detection. Due to its polar texture, the insect integument will react to
rapid changes in temperature, illumination, or uniaxial pressure in the same way as
nonbiological PE materials. It seems entirely possible, therefore, that the well-known
physiological reactions of various arthropods to such physical outside influences may be
related to the PE property of their integument (Athenstaedt and Claussen, 1981.)
A hard, relatively stiff material is a prerequisite for PE and PZE activity. The
mechanism of mollusc shell formation involving material deposition under the influence
of a steady polarizing field generated by the periostracum is very similar to the processes
used in industry to polarize piezoelectric ceramics and other materials (Zilberstein, 1972).
Since PZE activity is found in insects as well, one may entertain the possibility that insect
cuticle is formed under a polarizing field (during molting) just as the shell is in molluscs.
Standing waves in a mollusc shell (Limulus sp.) bounce back and forth within the
structure, generating a voltage whenever they impinge on the electrodes (Zilberstein,
1972). When the shell is placed in a damping medium, such as water, only the initial
response is observed. The natural state for many mollusks is in the water and this
response points toward an obvious sensory function especially in those molluscs which
seem to perceive sound despite the apparent absence of any recognizable sensory organ.
Sense organs for many electromagnetic freqiLeilcies have not been found in
insects, although several studies have shown that insects respond to these same
frequencies. It is worth repeating that the EM frequencies in question are not capable of
penetrating the insect cuticle to any degree (Presman. 1970). The depth of penetration of
EM waves into various tissues decreases with increasing wavelength. Therefore, one
may conclude that since the insects detect these wavelengths and since they cannot
penetrate the cuticle, the receptors cannot possibly be inside the insect, but instead must
be located on the outside of the insect. The countless sensilla found on the insect's
cuticle are the primary candidate for external receptors. A general function of antennae is
to amplify the incoming message. These sensilla may be detecting and amplifying low
levels of energy in the external environment that would otherwise be undetectable to
insects. It is known that organisms are sensitive to static fields and to EM fields of
various frequency ranges several orders of magnitude lower than the theoretically
predicted value (Presman, 1970).
If organisms can detect EM energy below background (noise) levels, then they
could be transmitting/detecting coherently. For example, although the power of
acupuncture lasers is low (only 2-5 mW) its spectral intensity is much larger than that of
sunlight (Kroy, 1989). Since all parts of the optic wave are in the same phase-rhythm,
correlated multiphoton effects such as interference-structures occur, making coherent
messages more complicated and therefore, increasing the amount of information
Fritz-Albert Popp (1989) has shown repeatedly that organisms transmit and
receive coherently. and a waveguide or resonator will tend to pick out coherent signals
from a noisy background (Diesendorf et al., 1974). Additionally, coherent oscillations
are able to perturb bio-communication systems, only by small amounts when the system
is under good homeostatic control, but by appreciable amounts when the system is under
biological stress (Smith, 1989). This means that a given organism may not be
equally sensitive to a particular radiation from one day to the next or even from one
moment to the next.
Dielectric Antennae: Possible Function in Insects
Critics have maintained that electrophysiological techniques should be employed
to determine whether a particular sensillum resonates to a particular EM frequency
(Diesendorf et al., 1974). One problem with this approach is that a dielectric system is
dependent upon a charge separation that must be maintained. Conductivity can be
adversely affected, or assisted, by the presence of pore canals or glands (Mankin. 1976).
Any leakage, such as a large hole caused from an improperly placed electrode, would
necessarily disrupt the system the researcher was trying to measure. The neuron might
still respond, but the system that regulates when that neuron fires would be compromised.
A negative result might then be misconstrued, and a positive result could not be reliably
understood to be a positive response.
Furthermore, the presence of a neuron or neurons, in the sensillum is not an
indication that they detect and/or transmit a neuronal spike in response to an EM
frequency. Instead, their presence may be only to increase the power of the sensillum,
which acts as an antenna. In other words, they would be driven elements. The increase
in power could result in an increase in gain, thus rendering the antenna (sensilla) more
There is the possibility however, that the insect detects radiation by means of an
antenna array. If this is the case, then the array should be examined and not the
individual elements. But how would one go about testing this possibility? An array
could be linked together directly beneath the cuticle. The sensilla responding to the EM
frequency would resonate thus vibrating the cuticle due to their close association. The
sensilla would then be viewed as collectors, and the underlying sclerite as the detector. A
neuron, or several, need only associate with the cuticle and not the sensillum directly. If
this situation were occurring, then the researcher's approach should focus on locating the
neurons dendritess) that innervate the cuticle.
Evidence supporting this hypothesis can be found on the cabbage moth larva.
Barathra brassicae. This caterpillar responds to low frequency sound stimuli with
defensive reactions (stoppintL, squirming, dropping). Minnich (1925, 1936) experimented
with tuning forks and the responses of various caterpillars and found sensitivities in the
30 to 1000 Hz range which is within the wingbeat frequency of all insects. The medium
vibration in the near-field (up to 70 cm) of a flying wasp is an adequate stimulus for the
hair as calculated by Tautz (1978). Eight filiform hairs mediate the sound sensitivity, but
only four hairs are necessary for a normal sound reception threshold response (Markl and
Tautz, 1975). Only two intact hairs revealed that the threshold response increased
threefold, and with only one hair, the threshold response increased sixfold. This
condition cannot occur without some degree of interaction/communication between the 8
This set-up has already been copied by man. The U.S. Department of Defense has
long known this since government documents were declassified back in the 70's showing
infrared sensors based upon the morphology of insect sensilla. The "spines" were non-
innervated tungsten detectors that were only 15 pm in length and 2-3 pm in width
(Callahan, i977b, p. 116) or 5-10 [lm long and situated in pits (Callahan, 1977b, p. 117).
These man-made sensilla are all attached at the base to a uranium dioxide plate and the
apparatus, called a "Thermal image projector-recorder", is used for infrared detection
(Redman, 1974). Much more recently, however, technology has progressed to where we
may now etch "microlasers" (Jewell et al.. 1991) on plates that closely resemble insect
sensilla in size, arrangement and shape (Callahan. 1977b, p. 117; Jewell et al., 1991, pgs.
87 & 94). The microlasers made at Bell Communications Research measure only one
micron or less, are arranged in nice, neat linear.arrays, and are elongated. As a matter of
fact, virtually any shape can be laser etched, so there is no reason not to believe that
insect sensilla can be replicated with stunning accuracy, if they have not already been by
certain agencies. Transistors having dimensions smaller than a micron are routinely
fabricated in numbers approaching tens of millions on a single conductor chip (Jewell et
The Office of Naval Research, for example, sponsors both man-made technology
in this field (Grossman et al.. 1991) as well as research on insect sensilla (Roshdy et al.,
1972; Chu-Wang and Axteli, 1973) including research dealing with the insect's ability to
detect electromagnetic radiation (Brown, 1963). Additionally, the U.S. Navy has utilized
(in the Second World War) a large rectangular array of 42 dielectric rods for gunnery fire
control purposes (reported in Kiely, 1953). Their support of studies investigating
arthropod sensilla has expanded our knowledge of these candid structures.
On the other hand, the sensilla may collectively receive the EM frequency as
mentioned above, but instead of directly causing a neuron to fire, they may alternatively
induce a physiological change to occur directly beneath the cuticle. The EM frequency
would then be detected by the insect as a physiological alteration, such as ion flow or
hormone release, which would in turn be detected by the insect in a completely different
part of the body. It is well known that some of the organic materials occurring in cuticle
and insect blood (-OH, -CH, -NH groups and others) absorb strong between 2.4 and 4.0
pm (Evans, 1966b). Sense organs should then be relatively thin, as in olfactory
chemoreceptors (Slifer, 1970) or transparent, such as occurs on Melanophila acuminata,
where the apparent absence of the exocuticle may allow for efficient far-infrared
detection (Evans, 1966b).
Because of the apparent difficulty in determining at what level we should test the
insect (which is how reductionistt science" works), the first line of inquiry might best be
made at the organismic or population level. Tautz (1978) obtained reliable behavioral
responses only from intact animals, and rarely from isolated segments when studying
caterpillars. Therefore, because both of these higher levels of investigation have proven
instructive in the past, the tests to conduct, at this time, should be behavioral.
A discussion on electromagnetic energy would not be complete without the recent
work on scatter phenomena. I have spent some time in the library reading books
searching for scattering phenomena concerning EM waves on various surfaces. My
search has shown that almost nothing is written from an entomological point of view, and
little useful information could be pulled from the facts that I understood. However, it is a
relevant topic, and most importantly, it has some bearing on this dissertation. Therefore,
I will briefly introduce some of the major points and facts concerning scatter phenomena
that I have picked up, and attempt to relate them to entomology as best I can.
Scattering theory and experimentation originated in the 1950's (Bennett and
Mattson, 1989). Researchers investigated such things as the scattering of radar waves
from the ocean surface. They measured the surface roughness of the Moon by analyzing
the distortion of the radar pulse backscattered from the Moon to the Earth. Physicists
studied the propagation of line-of-sight radio waves, some of which bounced off the
Earth, as well as the scattering of sound waves by rough surfaces. A review appeared
some ten years later entitled The Scattering of Electromagnetic Wave from Rough
Surfaces (Beckmann and Spizzichino, 1963) which contains over 300 references.
The best example of light scattering in insects concerns the blue morpho
butterflies. These butterflies do not possess the natural pigments in their wings so
common among other butterflies. Instead, the blue morphs have what is known as a
"structural color" rather than a "pigmented color". Visible light strikes the surface of a
blue morph and becomes scattered such that the emitted light is dependent upon the angle
viewed. Indeed, the wing color of the blue morpho changes from blue to various shades
of blue and purples while adjusting the viewing angle. The predominant scattering color
of blue is created from the diffraction/reflection patterns dependent upon the surface of
Although this example is well-known among entomologists, a lesser known
scattering phenomenon was observed in 1965 involving the corneal nipple array, which is
located on the surface of the compound eye of some insects. The corneal nipple array
functions by decreasing reflection (scatter) in the visible region while producing a
concomitant increase in the amplitude of the transmitted wave through the cornea
(Bernhard et al., 1965). The nipple array is actually an antenna array with a selective
absorption of EM radiation in virtue of its size in relation to the incoming wavelength
(size matching) and its impedance matching with the atmosphere.
A well known method utilizing scatter radiation for catching insects has been
utilized by many an entomologist for capturing nocturnal insects, which consists of
positioning a blacklight or a visible light, with a while sheet behind it as a backdrop. The
insects attracted to this trap will be attracted to the scattered radiation emanating from the
sheet and will largely ignore the actual light source. The type of scatter surface is
extremely important to the catch as Pickens and his colleagues discovered in 1994. Their
research found that a house fly trap involving a 40-W bulb and a reflector showed a
significantly larger catch when an aluminum reflector was used than a white plastic
Utilizing his knowledge of scatter phenomena, Callahan (1957) was able to
increase mating in the corn earworm above natural levels when he lined his mating cages
with aluminum foil. Anecdotal information only adds to this because Kaae and Shorey
(1973) once noticed that more moths and more mating pairs rested on illuminated leaves
than on shaded leaves during the full moon. Quantaince and Brues (1905) mentioned that
moths often congregated on stems of grass 20 to 50 ft. from an electric light, and
Callahan (1957) noticed that the corn earworm adults do the same around a blacklight
Molecular scattering takes on many different names depending upon the
properties. The system is complex, but there exists Rayleigh center scatter (or Cabannes),
Rayleigh wing Brillouin or Mandel' Shtam-Brillouin, Stokes and anti-Stokes Raman
wavelengths. These scattering wavelengths are reported to be highly predictable for
certain conditions such as coherent radiation. Under coherent conditions, for example,
Stokes and anti-Stokes wavelengths will occur exactly the same distance away (measured
in wavelengths) to the central coherent wavelength. What this means is that a coherent
wavelength emitted from a molecule, say 490 nm, will scatter radiation such that a Stokes
wavelength will be detected at 483 nm, and an anti-Stokes wavelength will be detected at
497 nm. These interference patterns are a characteristic of laser light (Jewell et al., 1991),
and because they are so reliable, it may be that these scattering %t a elengths. are used by
insects to assist in identifying a particular molecule. If this were so, one might expect to
find adjacent sensilla but of different sizes, set off by themselves, on the body of an
insect. One sensillum would resonate to the peak wavelength, while the other would
resonate to scatter frequencies, such as anti-Stokes. Their close proximity and likely
interaction (quite possibly already shown by Markl and Tautz in 1975) would enable the
insect to detect a particular coherent frequency absolutely.
The performance of an antenna, particularly with respect to its directive properties
is considerably modified by the presence of the earth beneath it (Anonymous. 1974).
This fact has been recognized for many decades at least, and many man-made antenna
arrays are designed with this factor in mind. One of the factors to consider is the
selective property of the ground. The effect of the ground can be to increase the intensity
of the radiation at some vertical angles and to decrease it at others. This means through
no inherent characteristic of the antenna itself, the antenna proper can be selectively tuned
to certain polarized frequencies by virtue of its interaction with the surrounding ground.
One effect of the ground is to simply reflect the incoming wave. This type of scatter is
If indeed a wave is reflected, then these reflected waves may interact with the
direct wave in various ways. This interaction will depend upon the orientation of the
antenna with respect to the ground, the height of the antenna, its length, and/or the
characteristics of the ground. Polarized waves can be unchanged or phase shifted 180
on reflection. Interaction of the incoming and reflected waves modifies the manner in
which the antenna receives it. Predicting the type and degree of interaction, however, is
mathematically very difficult. There is no question, however, that the interaction exists,
therefore, it needs to be taken into account in a discussion such as this.
The prevention of scattered waves from the ground, reflected or otherwise can be
achieved by conducting the received waves away from the antenna and was described in
The ARRL Antenna Book (1974) as such:
The ideal grounding system for a vertical grounded antenna would
consist of about 120 wires, each at least /2 wavelength long,
extending radially from the base of the antenna and spaced equally
around a circle. Such a system is the practical equivalent of
perfectly conducting ground and has negligible resistance. (p. 61)
This system, or anything resembling it, has not been seen by this student on any
insect. Therefore, I will make the assumption that some scattering off the insects's
cuticle is occurring, and so being, also must be considered into the discussion of EM
frequencies, insects, and antennae.
The number of different surface terrains found on insect cuticle cannot be covered
in this response, even if they were all known. It is often noted however, that sculpturing
of the integument is often species specific (Pilgrim, 1991a). Instead, I can only point to a
few examples drawing from my own limited experience.
Since reflection is the simplest scattering concept to understand, I will spend some
time discussing this. If one reexamines the quote just given, the number V2 or 0.5 seems
to jump out as being critical. If the area around the vertical antenna can be completely
conductive should a radial system be designed of at least half a wavelength, then
observing a similar radial phenomena in nature with similar dimensions would be good
circumstantial evidence for a scattering surface and that the insect used its sensilla as an
It may also be that electromagnetic waves may scatter off the insect sensilla
themselves. Just recently, Sajeev John (1991) described strongly scattering dielectric
microstructures. Certain dielectric microstructures have no propagating modes in any.
direction for a range of frequencies and exhibit what has been termed a "complete
photonic band gap" (John, 1991). Therefore, if insect sensilla are operating as dielectric
waveguides, then the presence of numerous adjacent sensilla could severely affect
scattering, which in turn affects how the antennae receives the wavelengths. This can
occur in three ways- constructive interference, destructive interference, and resonance.
Helical and corrugated sensilla are found on many insects. These sensilla types
may support the propagation of slow surface waves and thus find important application in
delay electronic devices (Callahan, 1975a). It may be that waveguides with helical
striations can discriminate between polarized FM 1 radiation. Already, we know that one
of the four basic characteristics of an antenna is its polarization (G.R.I.P.), therefore an
antenna can distinguish between two seemingly identical wavelengths but with different
polarizations. The helical striations of the waveguide would simply guide the wave in
one direction but inhibit radiation flow in the opposite direction. This would come about
due to the properties of the antennae acting as a surface waveguide where propagation of
the wave occurs on the outside of the antenna. What this means is that some insect
sensilla might be able to discriminate between enantiomers. since enantiomers differ only
in their ability to bend polarized light (Armstrong, 1989). Davis (1988) has shown that a
sensillum on a mosquito cannot discriminate between enantiomers. however, Kafka and
colleagues (1973) showed sensilla on both a grasshopper and the honeybee could
discriminate between enantiomers. How some sensilla discriminate between enantiomers
while others do not, should be explained by antennal morphology since all characteristics
of a particular antenna are irreversibly linked to its structural make-up.
Electromagnetic: an Overview
Electromagnetic waves were theoretically described for the first time by J.C.
Maxwell in 1864 and established experimentally in 1887 by H. Hertz. Electromagnetic
radiation is composed of two phenomena. The first is an electric field, and the other is a
magnetic field. These two phenomena orient perpendicular to one another while
interacting, and together form an electromagnetic field. Oersted first discovered the
effects of an electric current on a magnetic needle in 1820, and therefore, showed
(without understanding) the strong interdependence each field had for the other. Their
interdependence means they are not normally separated in nature, such that detection of
an electrical field usually denotes the presence of a magnetic field. Along the same line,
a change in either the electric or magnetic field will result in a change in the other. Even
though they are inextricably related, one important difference to keep in mind is that
electricity is an energy, while magnetism is a force, which means that a magnetic field is
able to do work. The biophysical properties of electrical currents and magnetic fields
differ. and these properties have important implications for sensory perception.
Electromagnetic radiation travels in sinusoidal waves through free space at the
speed of 300,000 km/sec, which was first established experimentally by A.H. Fizeau in
1849. They slow down when passing through a medium and refract, or bend, at all
interfaces where theie is a change in density. If the angle with which they strike a new
interface is severe enough, reflection is said to take place. Varying degrees of reflection
and refraction may occur depending upon properties of the new medium and the wave's
angle of incidence.
Electromagnetic energy does not all behave the same nor is it perceived the same
way by a given organism. This is due to the wavelength of the electromagnetic (EM)
wave as well as the energy it contains. For example, visible radiation can have very small
changes in wavelength, but our eyes perceive these subtle changes as completely different
colors (i.e. yellow and green). The radiations that have wavelengths longer than visible
light include infrared, microwave, and radio. The radiations that have wavelengths
shorter than v-isible light include ultraviolet, x-rays, and gamma rays.
The wavelengths in the visible range include what we call 'colors'. By definition,
these wavelengths make up collectively one 'octave'. All other EM radiation is invisible
to the human eye but, of course, can be detected by other means. Infrared radiation is
what most people refer to as heat. However, thermal, or convective heat can be produced
by almost any form of EM radiation, such as light rays, x-rays, and even high intensity
radar beams (Callahan, 1965a). Intermediate- and far-infrared energy along with near-
infrared together constitute 17 octaves, which means they span a range 17 times larger
than the visible wavelengths. Additionally, microwaves make-up 8 octaves. Scientific
papers dealing with the visible range and their effects on insects all far exceed the number
of papers associating the infrared or microwave wavelengths. Because these 25 octaves
have been relatively untapped by entomologists, there are countless potential discoveries
to be made.
Table 2-1. Infrared spectrum designated by wavelength range.
Infrared (familiar name) Wavelength range
Near-IR 0.8-2 pm
Intermediate-IR 2-15 pm
Far-IR 15-1000 pm
Generally speaking, the longer wavelengths are considered low energy and the
shorter wavelengths, high energy. This has led many researchers to believe that
organisms do not detect very long wavelengths because their energy is too low. or that
very short wavelengths are destructive to life because of their high energy, such as cosmic
rays producing chromosomal breakage in Drosophila melanogaster (Reddi and Rao,
1964). Smith and colleagues (1963) have shown a remarkable sensitivity among insects
to low-intensity radiation, which suggests that insects may have developed systems to
detect low intensity levels with which we are still unfamiliar. Although it is understood
that the most important wavelengths for organisms are in the visible, infrared and
ultraviolet regions, and that these wavelengths are short enough to be received selectively
and to penetrate the skin with moderate absorption, growing evidence does show that
apparently all ftrms of radiation are biologically active in some degree, even gamma
radiation (Brown, 1963) and x-rays (Smith et al.. 1963). The detection of these
apparently destructive wavelengths in vivo may in part be due to the fact that biological
systems have defensive systems for protection against the adverse effects of
electromagnetic fields (Presman, 1970). It follows that with adequate protection, an
insect may be able to use these particular wavelengths to their benefit.
Biological investigations have shown that organisms of the most diverse kinds-
from unicellular organisms to man- are sensitive to a constant magnetic field and to EM
fields of different frequencies (for reviews see Barnothy (1969), Presman (1970) and
Popp et al. (1989)). The effects of multiple exposures on the organism are sometimes
cumulative. Exposure to strong fields usually leads to adaptation to subsequent
exposures, whereas exposure to weak fields leads to progressively greater changes in the
organism (Presman, 1970). Surprisingly, some of these investigations have found an
effective energy tens of orders less than the theoretically estimated effective level. A
very important feature of these biological effects is that they are often produced by fields
of extremely low intensities. This naturally suggests that organisms have systems which
are especially sensitive to EM fields and as yet have no analogs in man.
In most cases, EM fields cause disturbances in the regulation of physiological
processes during embryonic development and during growth, which is the period when
the defense mechanisms do not exist or are not fully developed. Unfortunately, most of
the physiological mechanisms that lie behind biocommunication by means of
electromagnetic fields still remain unexplained (Breithaupt, 1989).
Interactions between organisms and EM fields take one of three general forms.
To some extent, they are all forms of communication and include:
1. The effect of EM processes taking place in the environment on the fimctioning
of living organisms.
2. The role of EM processes taking place within an organism in the vital activity
3. EM interconnections between organisms.
By means of EM fields and depending upon the frequency, information can be
transmitted through any medium inhabited by living organisms and in any meteorological
conditions- during the polar day or night, in river and sea water, within the earth's crust
and finally, in the tissues or organisms themselves. Additionally, reports indicate that
entire organisms are most sensitive to EM fields, whereas isolated organs and cells are
less sensitive, and solutions of macromolecules even less so (Presman, 1970). Tautz
(1978) came to the same conclusion when studying the vibration receptor hairs on the
caterpillar, Barathra brassicae, when he found that recordings from hairs needed to be
made from intact animals because it was not possible to get reliable responses over
sufficient duration from isolated segments.
For this reason, when studying the effects of EM fields on organisms,
reductionistt science', such as electrophysiological experimentation, may not be as
effective a scientific methodology in reaching the correct conclusions as will sound
behavioral experimentation on whole organisms or even populations of organisms.
Investigation of these functions must proceed from complex biological systems and
processes to progressively more simple systems and processes. This gradual descent
down the hierarchy of systems should help to avoid the confusion that is so often
generated by conflicting results conducted upon separate parameters of the same system.
All EM fields are based upon waves. Most of these waves may take the classic
form of a sinusoidal wave, however, other waves or oscillations may impinge upon these
waves thus forming a modulated wave. The sinusoidal waves vary only with sine and
cosine laws, but modulated waves vary with the perturbing wave as well as the carrier
wave. Obviously, these modulated waves are more complex but always include
additional information that may be necessary for communication. It is important for
living systems to have highly coherent carrier oscillations for purposes of bio-
communication, but the effects may well be generated by modulation of the carrier wave.
For example, Smith (1989) reported that human patients who complain of allergic
responses to microwave cookers often show on testing no reaction at the microwave
frequency when it is highly coherent. However, they react strongly when the frequency is
modulated with extremely low frequencies commonly generated while the turntable in the
microwave cooker rotates. Furthermore, radio communications transmitted or received
by helicopters are often modulated by the spinning rotors (Warnke, 1989b).
For insects, waves may be modulated by the 60 (Hertz) Hz "flicker frequency"
alternating electric field in the United States (50 Hz in other countries). The exoskeleton
of insect antennae is highly reflective of visible radiation (Callahan, 1990). This means
an insect within the vicinity of an alternating current will be flickering, by virtue of
reflection, at that frequency. If the insect is indoors under artificial lighting, then this
flickering of visible wavelengths off the insect's body could very well be modulating any
That organisms respond to varied forms of EM radiation should not come as a
surprise to any scientist who is aware that electromagnetic radiation must have existed
before life began (both Genesis, 1:3 and Keeton and Gould, 1986) and that all life
absolutely must have developed under its influence. The influence of the chemical
environment has often been pointed out, while another part, the electromagnetic
environment, has too often been neglected (Kroy, 1989). Living systems are subject to
the laws of physics and particularly the physics of electromagnetic fields, just as much as
they are subject to chemistry. However, not all life will respond in the same way to these
fields and one challenge is to determine how a particular organism responds to various
forms of FX1 radiation.
The short-term effects of EM fields on the behavior of animals is revealed in
changes in general motor activity, attempts of the animal to escape from the acting factor,
and orientational reactions to EM fields. Smith (1989) reported that human subjects could
develop allergic reactions when exposed to particular EM fields. In general. Smith
continued, there are many biomedical systems which have reported sensitivities to low
level electromagnetic fields. Laboratory experiments with Euglena show that when
exposed to a frequency of 5-7 Megahertz (MHZ) they orient, in motion, parallel to the
electric lines of force (reported in Presman, 1970). Additionally, specific motor reactions
of paramecia to EM stimuli of various kinds have been reported (Presman, 1963a,b).
Long-term effects of EM fields on the behavior of animals are often revealed in
one or more delayed responses usually measurable as physiological changes or as delayed
behavioral responses. Keplinger (1958) exposed the back of a rat to intense 1.25 cm
waves, which are completely absorbed by the skin. This led to high-frequency
oscillations of the biopotentials commencing fully seven minutes after irradiation. The
slow response often shown in response to various stimuli is eloquently described by
Aladzhalova in 1962 with regard to brain activity.
One of the characteristics of the slow control system is the fact that it does
not react to an insignificant single (chance) external disturbance. Its
reaction to an environmental factor acting more or less systematically
takes several hours and can be directed not only towards overcoming the
produced changes in the internal environment, but also towards active
alteration of the level of activity with due regard to the possible effect of
the new factor. (quoted from Presman, 1970)
In many cases EM fields cause disturbances in the regulation of physiological processes,
mostly during embryonic development and during growth (the period when the defense
mechanisms do not exist or are not fully developed). An examination of the nature of
these disturbances indicates they are due to the effect of the EM field on the EM
processes specifically involved in the regulation of physiological functions (Presman,
An interesting theory also maintains that natural and artificial fields affect
biochemical processes in organisms by affecting the water in which these processes take
place. Water is involved in almost all biochemical processes, either directly or indirectly.
Therefore, if water could store energy, it could influence the biochemical processes that
involve it. This hypothesis finds supnorl from researchers who have determined that
coherent EM fields can be stored in HO for more than a month after exposure (Choy et
Some animals do possess sensory organs apparently designed for the detection of
EM fields or waves. Well known examples include electrosensitivity in many fish such
as the hammerhead shark as well as the bill of the platypus, the detection of ultraviolet
radiation by the bee, and infrared prey detection by snakes and owls. Humans do not
possess these capabilities, so understanding these abilities is more difficult for us to
comprehend then, let us say, vision, which is surprisingly similar across many animals.
Certain exceptions do turn up occasionally, such as the eye of slugs, which has been
shown to respond to IR radiation (Newell and Newell, 1968).
Sensory perception may be involved with physiological changes or morphological
changes in organs and tissues of animals produced by a single exposure to EM fields of
high intensity or cumulative effects from repeated exposures produced by low-intensity
EM fields (Presman, 1970). Indeed, there may be specialized sense organs that perceive
these stimuli, such as the ampullae of Lorenzini on a shark's snout (Kalmijn, 1977),
which are sensitive to weak electrical stimuli produced by muscle contractions of bony
fish and are, of course, important to the shark for detecting its prey. These organs can
respond to fields as small as one microvolt per meter (Kalmijn, 1977; Murray 1965)
which is several orders below typical action potentials (Jungerman and Rosenblnm.
Electromagnetic "auras" called electroauroagrams were detected 25 cm from an
isolated frog nerve (1 mV), isolated frog muscle and heart at a distance of 14 cm, and
human heart and muscle at a distance of 10 cm (Gulyaev, 1967; Gulyaev et al., 1967).
Detection of these fields is likely for many animals, because many terrestrial animals,
including various species of insects, birds, and furred animals, produce electrical fields of
relatively high amplitudes (Warnke, 1973; 1975). The wings of flying insects and birds
together with their surroundings are working as electric field generators, which build up
relatively strong Coulomb forces at the outside surface (Warnke, 1989a). Electrical field
intensities from animals in wind channels were reduced to nearly zero when metal wind
channels were used. Wind channels made from wood were more similar to electric fields
determined in the open air (Warnke, 1989a).
Detection of Electromagnetic Fields by Insects
Insects are a strange crew, but this is what makes them so interesting to me. They
exhibit various behaviors that cannot be explained by conventional theories, but are
consistent with the hypothesis that insects detect electromagnetic radiation. One of these
apparent anomalies concerns the ant, Trachymyrmex septentrionalis, which always builds
mounds with a slope in one predominant direction. Tschinkel and Bhatkar (1974)
reported that destroying the mound prompted the workers to build a mound facing the
same direction to within 3.20. Some common environmental factor to which this species
oriented seemed improbable because each ant colony chose an orientation independent of
adjacent colonies, and yet each one would rebuild their same mound in the same direction
after it was artificially destroyed. On the other hand, mound orientation just might be
explained by an environmental factor influencing the individual colony, since bringing
the colony indoors causes them to make a completely circular mound. How all the
workers come to agree on building a mound with the identical orientation is yet another
question waiting for an explanation. Could electromagnetic waves be directly affecting
this behavior either in the environment or via intraspecific communication? Examples
will follow of how social insects may be utilizing EM fields for communication purposes.
It is possible for high electrical field intensities to occur at the tips of antennae.
This can be visually depicted as an intensive bunching of the field lines, or peak current
conduction. The same basic process occurs at the microtips of an insect's body (Warke,
1989a). Charged particles selectively adhere to insect sensilla when the cuticle itself is
charged (Warnke, 1989a). This knowledge had been used for years by NASA wherein
electrets were used to collect charged particles and vapors from the air in pollution
studies (Pillai et al., 1974). No attraction of charged particles occurs toward insect
sensilla when no electrical charge has been applied to the underlying cuticle. Indeed.
many researchers have independently determined that the concentration of molecules can
be several orders of magnitude higher on the cuticle layer, after just one second, than in
the airstream by which they were introduced (Adam and Delbrick, 1968; Steinbrecht and
Kaissling, 1974; Mankin et al., 1977; Kasang. 1978).
Contact chemoreceptors or gustatory chemoreceptors have a terminal pore at the
tip. It was discovered by Callahan (1975a) that charged particles are attracted to the
electret properties of the sensilla and move along the trichodea to this single pore where
they collect in clumps.
Light produced at the tips of structures comes from gas molecules that have been
excited to release energetic electrons during collisions with an avalanche of electrons.
The avalanche is caused by the strong electric field that propels electrons from the
pointed exposed surface where forces binding ions to the surface are weakest (Golde,
1973). This action results from the "point effect" which states that electrical field
intensity will be highest at the tips (i.e. St. Elmo's fire).
Biological matter lighted by strong electrical fields is not uncommon in nature.
Schonland (1950) measured point discharge from plants. He found that during
thunderstorms the flow of electricity to earth was considerably greater than the flow from
earth during fair weather. If a thunderhead is particularly heavily charged he noted that
even leaves and blades of grass may glow at the tips because of intense ionization
Callahan and Mankin (1978) subjected five insects to a large electric field and
they all emitted visible glows of various colors as well as ultraviolet. The insects
displayed bluish white light from various external points on their bodies such as the distal
tip of mandibles, ovipositors, antennae, leg joints, and red, green, or orange flares at or
near the spiracles. Any species of insect can be made to emit visible radiation if it is
placed in an alternating electric field between 2 to 3 kV/cm (Callahan, 1980). The areas
that light up are also the areas that contain the sensory organs.
Insect sensilla can be stimulated mechanically in regions adjoining highly
resistant structures (sclerites) because of increased field intensities. This suggests that the
assimilation of electric fields is ultimately reduced to the detection of mechanical energy
Detection of electromagnetic energy can be accomplished by insects in several
ways. Bees regularly pull their antennae through a cleaning gap (antenna cleaner) at the
frontal extremities, thus positively charging them (Warnke, 1989a). In fact, virtually all
insects are known to do the same thing. Any dielectric having a conductivity greater than
that of air will decay to zero after a short time (Mankin, 1976). For this reason, insects
should be continually charging themselves, which they do, maybe in an effort to
compensate for this problem.
Simply stated, a charged antenna will be able to detect charged particles.
Electromagnetic fields around insects created by the atmosphere should be more
pronounced in flying insects, due to the grounding effect when in contact with the earth's
surface. This means insects should be more sensitive to certain EM fields during flight,
and many insects do search for scents while on the wing.
Entomologists are aware that insects seek shelter during rainstorms which
traditionally was explained as an escape response to the highly dangerous rain drops
plummeting from the sky. Man-made dielectric antennae do not work efficiently when
dew or excessive moisture collects on them (Kiely, 1953), so reason dictates that if
insects use their sensilla as dielectric antennae, avoiding excessive moisture would be in
their best interest. Additionally, the electromagnetic field strength accumulating at tips,
as described above, is predominantly a function of the relative atmospheric humidity
Bees are particularly aggressive when subjected to high atmospheric activity in
the 10-20 kHz range (Warnke, 1973). If this action came about through changes in
electric charges about the bee, then one would expect action on the part of the bee in
response to this change. Groups of bees kept in earthed metal cages with a relatively high
atmospheric humidity will lose their charges. The immediate fluttering of the wings
which commences may occur in an effort by the bees to recharge themselves through
friction with the air. Indeed, as soon as atmospheric ions are added to a Faraday cage,
fluttering ceases abruptly (Warnke, 1989a). Frictional or tribolelectric effects contribute
strongly to an object's charge density. A beeswax disk freshly washed in distilled water
exhibited a surface charge density of 12 x 10-" cl/cm2, however, scraping it only once
across a paper towel increased the charge density to 1.9 x 10-9 cl/cm2 (Mankin, 1976).
Beating wings of flying insects produce extremely low frequency (ELF) radio
emissions and are detectable with a tuned radio frequency radio receiver (Koemel and
Callahan, 1994). Different ELF frequencies can be produced by the two wings and one
noctuid moth produced seven nonharmonic radio frequencies simultaneously. In fact,
more than 5000 samples of flying insects, tested one at a time, produced radio frequencies
(Koemel and Callahan, 1994). Electromagnetic fields created during the flight of the
bumblebee and mosquito were also detected by Gulyaev and his co-workers over twenty
years ago (Gulyaev, 1967; Gulyaev. et al., 1967).
At the other end of the electromagnetic spectrum, Hudseph (1970) found the
maximum radiant energy across the moth blackbody5 to be highest between 7 and 14 Pm.
These infrared wavelengths are only the maximum values in a wide range because every
object at a temperature above absolute zero emits infrared radiation (Barnes. 1963).
Callahan and Lee (1974) found the corn earworm moth to emit a 10 pm infrared signal
which is chopped (modulated) by the wings. When all insects fly, they raise their
background temperature to a considerable degree above the background temperature of
the atmosphere (Callahan, 1968). Earlier research by Duane and Tyler (1950) compared
the total emission spectrophotometric curve of the cecropia moth with that of a blackbody
at the same temperature, and reasoned that the male could detect a female in the 3 to 11
apm region against a cool night background. Fifteen years later Callahan (1965c) reported
5A blackbody is any object that absorbs or receives all infrared radiation. Objects
that absorb in lesser degrees are termed 'gray bodies'. Blackening a surface will help to
approach the ideal blackbody (approaches unity). A mirror radiates and absorbs infrared
wavelengths poorly and therefore has an emissivity close to zero.
that the corn earworm moth could detect an infrared emitter in the 8-13 pm range in a
totally dark room. Callahan (1965c) calculated that the moth thorax, Herse cingulata,
would be easily detectable to a receiver up to 1 km away when taking into account the
body temperature and wattage produced. The fact that these moths, and no doubt others,
emit infrared in the same range that they are designed to detect, points to the likelihood
that moths use this system as a navigational aid. Indeed, Hackforth simply stated in 1960
that 'any object at a different temperature than the surroundings can be detected'. It is
reasonable to assume that moths, and other insects, have taken advantage of this fact.
Body lice were found to be more attracted to the blackbody side of an
experimental set-up over an aluminum (reflective) side, even though both were
maintained at the same temperature (Broce, 1971) Additionally, this orientation toward
a blackbody infrared (IR) source was accomplished in the absence of convective heat.
Broce explained this response as a necessity for the newly hatched larvae to find a host.
The lice detected this blackbody source at a distance of 3.25 cm, but were unable to do so
at 4.75 cm. This threshold distance agreed with the threshold distance for bedbugs as
reported by Rivnay (1932). Hence, the reaction to blackbody IR is advantageous, because
by actively moving only when the host is in close proximity, the chances of being
rewarded by a blood meal are increased.
The wavelength of peak intensity for a warm-blooded animal is ca. 9.5 pm
(Bruce, 1971). Therefore, the emissivity in the infrared for homing in on a moth might
not be too different for homing in on a human. Human skin is an almost perfect emitter
of infrared radiation in the spectral region beyond 3 microns (Barnes, 1963). Emissivity
is a direct function of absorption, and since absorption in turn is a function of wavelength,
it follows that any given object may be transparent for one part of the spectrum and
totally absorbing or "black" for other wavelengths. For example, human skin is relatively
transparent to visible light and to infrared radiation of wavelengths shorter than about 2
rtm. Therefore, skin pigmentation produces great differences in the absorptive and
reflective power of skin for these parts of the spectrum. However, this pigmentation
plays no role in the longer wavelength region (Bares, 1963). All humans, regardless of
race, were indistinguishable when viewed under infrared devices (Barnes, 1963).
Research in the infrared had led to earlier developments like the Sniperscope, the heat-
seeking head of the Sidewinder missile, the horizon sensors used in the stabilization of
spacecraft, the temperature-measuring radiometers of the Tiros weather satellites, and the
Venus probe, Mariner II. A wide assortment of sensitive infrared instruments are
available for passive detection, temperature measurement, communication, e ien itg, and
thermal photography, (Barnes, 1963).
Response of Insects to Electromagnetic Fields
Much of the research conducted with insects and EM radiation focused on killing
or injuring the bugs (Nelson, 1967; Frings, 1952), and not upon any communication
system. Tilton and Schroeder (1963) killed immature insects in kernels of rough rice by
treating with a gas-fired infrared heater. Nelson and Kantack (1966) used a 39 megacycle
radio frequency which killed all stages of the Indian-meal moth in a matter of seconds.
Microwaves (12.25 cm) were used to kill the granary weevil and the flour beetle as
reported by Baker and his colleagues in 1956. Radio frequencies were again chosen to
kill the wax moth (Nelson. 1967) and rice weevil (Nelson and Stetson, 1974), where
death was generally thought to come about through differential heating of the insects vs.
the foodstuff (Nelson and Rhine, 1966). For example, Nelson (1967) calculated the
heating rate for rice weevils to be 1.8 times the heating rate for the wheat. The
distinguishing feature between these "killing" frequencies and communication
frequencies lies in the energy of the wave. These wavelengths can theoretically be used
by insects for communication. However, their ei-ergy must be reduced substantially.
W.H. Whitcomb, his student, J.C. Nickerson, and Callahan collaborated on a short
research project involving a worker ant, Conomyrma insana (Buckley), and infrared
emissions (Callahan et al., 1982). They found that the worker ant was attracted to the far-
infrared emissions from wax and petroleum candles (remember, heat is generally
associated with near-infrared). The results were determined by utilizing selective filters
designed to block out certain wavelengths. Radiation emanating fiom the candle in the
visible range was not attractive to the ant. However, if filters allowing far-infrared to
transmit were used, the worker ant made a "bee-line" directly towards the source and
after reaching a point ca. 5 cm (or less) from the base, kept circling the candle similarly to
a moth circling a lightbulb or candle flame. It is likely that far-IR detection can be
accomplished by sensilla of appropriate size, however, there is also the possibility that
insects may "see" IR radiation via the ommatidia (Callahan, 1965b) or ocelli (Callahan,
Various species of moth and larvae were subjected to infrared radiation with
wavelengths in the 1-30 4m band (Callahan, 1966). High intensity infrared focused into
the eye killed moths in an average of 60 sec. at 120'F. Low intensity infrared focused on
the antenna or eye elicited flight, antenna responses, or sexual responses, at 85 to 92 F.
Low intensity infrared at 92F focused on the ocelli of larvae elicited fecal pellet
deposition, searching, and head scanning. Fifth instar corn earworm larvae were
subjected to the radiation for 15 to 40 sec., before becoming active, which consisted of
depositing a fecal pellet, chewing with their mandibles, and moving toward the IR source
while scanning it with the head. Noctuid adults responded by \ ibr;ting their antennae
immediately. The coiled proboscis immediately went into a frenzy of movement.
Curiously, sphingid moths and saturniid moths were much slower to respond with
antennal movements. The four species of night-flying arctiid moths were by far the most
sensitive. They all responded by curving the abdomen and feeling toward the source with
both legs and antenna, and attempted to touch with their abdomen objects brought within
their range. One second of high-intensity radiation of 1 to 30 Pm elicited flight and
sexual responses from these four species for a period of 10 to 20 minutes. Five to ten
seconds of low intensity IR induced similar responses.
Work in England with the rusty tussock moth, Orgyia antiqua, gave indirect
evidence that this species is attracted to the opposite sex by high frequency radiation and
individuals of this species were found to orient upwind in response to the presence of the
opposite sex (Laithwaite, 1960). Fabre (1912) also reported orientation between insects
upwind of one another. Laithwaite further speculated that the pectinate antenna of the
male serves as a diffraction grid for reception, presumably of the female, and was one of
the first researchers to suggest that insect antennae might be capable of detecting
Four years later Evans (1964) showed that a buprestid beetle. Melanophila
acuminata, possessed a distinct infrared sense organ located not on the antenna, but on
the mesothorax adjacent to the coxal cavities. Although several reports had found that
insects, such as mosquitoes (Burgess, 1959), respond to infrared, this was the first
reported insect infrared organ. The radiation used to elicit a response was incoherent
infrared radiation between 0.8 and 6.0 [im, with a maximum sensitivity between 2.5 and 4
pm (Evans, 1966a). Evans felt that these sense organs responded to IR radiation
produced from forest fires many kilometers away, possibly 100 kilometers or more
(Evans, 1964. 1966a). Responses measured included a form of antennal twitching on the
side of the body being stimulated, and this only occurred when the sensory organ was
stimulated, not the antenna. In fact, stimulation of no other part of the body could elicit
this reaction. The twitching response occurred only after exposure to the radiation for as
little as 33 msec, which points toward a legitimate radiation detector and not a response
by means of some secondary reaction to convective heat. This discovery does not,
however, preclude the beetle's sensitivity to heat as well. When light from microscope
light is filtered to allow only wavelengths greater than 1 uim (near infrared) to pass,
beetles will aggregate on the side of the cage where this stimulus is presented (Evans,
1966a). Additionally, beetles aggregate toward a heated element in the cage. Beetles
lose this ability after antennectomy (removal of the antennae). This suggests that near-
infrared incoherent receptors may be located on the antenna, while far-infrared to
intermediate-IR coherent receptors may be located within the specialized infrared sense
organ (Evans, 1966b).
Adult females of the spiny rat mite, Laelaps echidnina, also respond to incoherent
infrared radiation in the narrow band between 4.4 and 4.6 Irm (Bruce, 1971). Much like
Melanophila. the behavioral response consisted of rapid vertical movements or a single
laterally directed movement of the forelegs. The spiny rat mite is able to discriminate
among several IR wavelengths and is able to accomplish this at relatively low intensities.
These mites have no optical system, and they live in virtual darkness. The predominant
sensory structures on the body are numerous setae. On tarsus I of the foreleg, tapered
setae are Ihe only observed sensory structures.
Infrared detection had already been shown with other insects, such as the
mosquito, but the response, probing behavior, was reported to be elicited in response to
thermal or convective heat as well as to moisture (Burgess, 1959).
Incoherent radiation sources were incapable of eliciting reactions in moths
(Eldumiati and Levengood, 1971; 1972) as well as coherent radiation from Klystrons (0.8
to 3.5 cm), a Gallium Arsenide diode (0.85 gim) or a pulsed near-infrared laser. Positive
results were obtained by Callahan (1968, 1969) who first used coherent radiation from
lasers in insect behavioral experiments. Tests using a cyanide laser at the Georgian
Institute of Technology6 demonstrated that the-corn earworm moth. Heliothis zea
6USDA Coop. Agreement (1966) 12-14-100-9071 (33); Final Report Project No.
A-985, Dec. 1970, Georgia Institute of Technology.
(=Helicoverpa zea) did respond by attraction to 337 pm radiation. This finding was
supported by Eldumiati and Levengood (1971) who additionally found that the corn
earworm and the fall arnnyworm, Spodopterafrugiperda, were strongly attracted to
radiation of 311 pm wavelengths. Additional experiments indicated that the 337 pm
wavelength induced changes in the activity of the moths and reduced mating potential
(Eldumiati and Levengood, 1971). Under different conditions, Turner and colleagues
tested corn earworm, fall armyworm, and cabbage looper adults (Trichoplusia ni) but
found no attraction toward 28, 118, or 337 tpm radiation produced by a laser (Turner et
Just a few years later the Glagolewa-Arkadiewa "mass radiator" was used to
further test the response of insects to pure electromagnetic radiation. The mass radiator
was used to transmit far-IR radiation upon several insects in order to record their
behavioral responses, if any (Callahan, 1971). The responses were armaing All insects
tested responded to the mass radiator with antennal movement. Three mated corn
earworm females were stimulated to oviposit within a few seconds of exposure to the
radiation. Wasps immediately exhibited the antennal cleaning response, and fire ants
responded by violent movement of the legs and antennae. Not a single response from any
of the insects tested occurred when the antennae were cut off. One year later, Eldumiati
and Levengood (1972) found extremely strong attractive responses of insects to far-IR
radiation as well.
Electrophysiological responses were obtained from a saturniid moth when the
antenna was exposed to incoherent as well as coherent light of 6328 A (633 nm) low
intensity laser radiation (Callahan, 1968). The fact that antennae respond to visible
frequencies was just as important a discovery as the response to coherent radiation.
Behavioral responses to broadband IR in the 1-15 mtnl range (far-IR) have been reported
from H. zea (Callahan, 1965b), Aedes aegypti (lMangumr and Callahan, 1968) and a
braconid wasp, Coeloides brunneri (Richerson and Borden, 1972). Responses to
narrowband radiation in the range 2-6 urn have been reported for Melanophila acuminala
(Evans, 1964) and for an acarine, Laelaps echidnina (Bruce, 1971).
The red imported fire ant, Solenopsis invicta, is attracted to electric fields (Gnatzy
and Tautz, 1977). Attraction is directly proportional to field strength for both DC and AC
current. Ants began to leave the source within seconds of the electrical source being
disconnected, but the response was longer for the AC current which suggests that they
may be able to differentiate somehow between AC and DC current. Other than this, no
other behavioral differences could be distinguished from their responses to either DC or
When the electrical disks were covered with a plastic wrap. the ants no longer
responded. These results suggest that the ants may have to come into contact with the
conducting material to respond (Gnatzy and Tautz, 1977). The plastic wrap need only be
13 [tm thick to prevent any response. Since an electromagnetic field can easily penetrate
plastic wrap, the possibility exists that exposed conducting material may be necessary for
detection. It also may be that a thin molecular layer may exist on the disks which in turn
may be "pumped" by the electrical field (see section on molecular emissions). The
observed responses could not have been a -n:liL'ral' attraction since the ants responded to
voltages of less than 10 V, but they responded proportionally up to 110 V (energy far
above that found in nature) even though the ants could electrocute themselves quite
nicely at 60 V.
Interesting orientation reactions have been observed in ants whereby a super high
frequency (SHF) field (10,000 MHZ) caused the insects to orient their antennae along the
electric lines of force (Jaski, 1960). Additionally, the ants lost the ability to
"communicate" the location of food to other ants (Jaski, 1960). It is of interest that the
length of the antennae of the large ants used in these experiments was almost a quarter of
the wavelength. A relation between wavelength received and length of the ants' antenna.
suggests the antennae proper are operating as electromagnetic antennae. Insect antennae
are hollow and are covered with wax, which further means that the antennae may be
operating as tubular dielectric waveguides. Other experiments with ants indicate the
possible existence of intercommunication based on ionizing radiation (Khalifman, 1965;
The effect of electrical fields upon social insects may be more profound than the
effects upon solitary insects since communication is so vital to the existence of insect
sociality. This communication process, which is at the moment not well understood, may
be mediated by electromagnetic phenomena. Not only ants, as I have mentioned in the
paragraph above, but bees when subjected to an alternating electric field are also no
longer able to recognize one another (Warnke, 1989a). Additionally, the highly social
activity of gallery building in termites is influenced by electric fields. When the termites
were shielded by various metals, earthed or unearthed, gallery-building was suppressed
for about 8 to 14 days, compared with unshielded groups (Becker, 1976a).
An electrical field gradient of 10 to 62.5 V/cm immediately reduced the activity of
Drosophila but had no effect on the blowfly, Calliphora (Edwards, 1960a). During the
period of reduced activity, those insects who were not walking about were usually
observed vigorously rubbing together their front legs and cleaning their wings. Both E.C.
Okress (reported in Callahan, 1967) and Warnke (1989a) hypothesized that insects do this
in order to recharge certain cuticular regions of their body. Edwards stiggestdJ.that the
response of these insects was based upon the detection of the accumulation of charges,
possibly static charges, on their body (although no mechanism as to how the insects
accomplish this was given) and that larger insects may distribute the charges more
effectively, therefore explaining why the larger fly, Calliphora. was not affected while
the smaller fly, Drosophila, was.
Picton (1966) showed that Drosophila respond to weak magnetic and electrostatic
fields, and Levengood (1962) found that an electric field affected Drosophila growth
which he attributed to variations in air-ion densities. Schneider (1975) showed
orientation in the beetle, Melolontha vulgaris, is strongly affected by electric charges, and
Maw (1961) discovered that the rate of egg-laying increased when the insects were
screened from fluctuating (modulating) natural EM fields in the presence or absence of an
artificial electrostatic field of 1.2 V/cm (close to earth's electric field.) The same effect
was observed when the natural fields were excluded, and replaced by artificial fields (0.8
V/cm) that fluctuated like natural fields.
Anecdotal information about Diptera (flies) increasing their activity before a
storm are thought to be related to these electrical charges. Although Edwards (1960)
could not support the claim that this behavior was dependent upon potential gradients
found in nature, he was able to increase flight activity of Calliphora vicina by increasing
positive-ion densities above that which would be found in nature. Peak activity was
found to occur about 45 minutes after first exposure, however, the flies acclimated about
15 minutes after the peak and remained so. No effect was observed with negative ions.
Becker (1963b) found that electrostatic fields 100 x greater than the earth's electric field
rendered flies inactive.
Electric fields might also act as a stress stimulus. Bee swarms became very
restless when exposed to an electric field of 11 kV/'m, and the swarm temperature rose
sharply (Warnke, 1976a,b).
Defense of social territory was intensified to such an extent that members
of the same swarm attacked one another. After a few days of the field
influence the bees tore their brood out of their cells, and no more fresh
broods were established. Similarly, honey and pollen were used up and no
more was collected. Bees which had been placed in their hives only
shortly before the beginning of the experiment, left the hive again
regularly during the period of electrical field influence. On the other hand,
bees which had already become used to their hives before the experiment
began to seal up all crevices and holes with propolis, including the hive
entrance. Lack of oxygen led to intensive wing-fluttering, causing a sharp
rise in temperature and the eventual death of the insects.
(Warnke, 1989a, pp. 82-83)
Highly sensitive swarms showed measurable reactions to field intensities of 100 V/m at
frequencies between 30 and 40 Hz, whereby when the field was applied, all their wings
suddenly began to flutter at a rate of 100-150 Hz.
The response of insects to magnetic fields, specifically the geomagnetic field, has
been demonstrated repeatedly. Both the beetle, Tenebrio, and the sandhopper. Talitrus
saltator. were found to orient to the earth's magnetic field in complete darkness
(Arendse, 1978), while the beetle, lMelolontha vulgaris, is strongly affected by magnetic
fields (Schneider. 1975). The orientation of the bee dance on a vertical hone, comb is
affected by very small experimentally induced alterations in the ambient magnetic field
(Lindauer and Martin, 1968; Lindauer, 1972). Some evidence exists that ants may sense
the geomagnetic field (Markl, 1962). Cockchafers, bees, crickets, wingless temnitee. and
many flies were found capable of orienting to the geomagnetic field (Becker, 1063a.b).
In particular, flies almost always land in an east-west or north-south direction with
respect to magnetic north and irrespective of the sun's location. Resting flies maintain
this direction or alter it by rapid 90 movements (Becker and Speck, 1964). One
interesting result they found was that dead flies suspended on long threads reacted to
magnetic fields as well. In reference to magnetic fields, this noted effect upon dead flies
may very well be related to the behavior of live ones.
Becker found that in the field of a permanent magnet 100x stronger than the
geomagnetic field, insects become excited, but after some time they orient themselves
parallel or perpendicular to the magnetic lines of force. Very strong magnetic fields
suppressed insect activity he found as Kisliuk and Ishay (1977) also discovered with the
hornet, Vespa orientalis. These two researchers found that an additional horizontal
magnetic field is lethal for adult hornets and larvae, but the juvenile hornets are capable
of adaptin., although not before they remained relatively motionless for 4 or 5 days.
Kisliuk and Ishay (1977) showed that comb-building in Vespa orientalis is highest in
regions of high-field intensity and progressively lower in regions of low-field intensity,
while Martin and Lindauer (1973) found honeybees to respond to a 10-fold increase in
the magnetic field by building cylindrical combs fastened to the floor rather than the roof.
A mechanism, or even a specific receptor mediating these responses to magnetic
fields in insects was unknown. Bacteria had been found to contain intracytoplasmic
membrane vesicles rich in iron (Blakemore, 1975) but it was not until 1978 that Gould
and associates (Gould et al., 1978) discovered ferromagnetic particles, magnetite, in the
honeybee abdomen. Later, Jones and McFadden (1982) discovered magnetic material in
the body of the monarch butterfly. The earth's magnetic field is equivalent to 0.5 to 0.7
gauss (Zimmerman and Rogers. 1989), the variation due in part to the seasonal changes
and particular location on the earth (Prolic and Nenadovic, 1995). Additionally, the
vertical component of the earth's magnetic field has a greater magnitude than the
horizontal (Blakemore, 1975). Honeybees can be trained to respond to very small
changes in geomagnetic field intensity (Walker and Bitterman, 1989b). This sensitivity is
suspected to aid in navigation when foraging away from the hive. Walker and Bitterman
(1989a) also attached magnets to honeybees and successfully impaired magnetic field
discrimination. Since these magnets were placed above the magnetite crystals on the
abdomen, it was implied that these crystals may be involved in detecting the geomagnetic
The position of vertical galleries built by the termite. Heterolermes indicola, was
found to be influenced by the weak alternating magnetic fields generated by the electric
heater in an air-conditioned basement testing room (Becker. 1976b). Becker used earthed
hardboard plates coated with silver paint thus excluding the electric field component (E),
but allowing the magnetic field component (H) of an E 1I field to permeate the plate
unhindered (Becker, 1976a). At a distance of about 2 m, the intensity of the alternating
magnetic field was lower than 1 gamma (y) and yet the termites could still detect the field
from this distance. These results came after similar work which found feeding activity is
influenced by disturbances in the geomagnetic field in a 27-day rhythm (Becker, 1976b;
Becker and Gerisch, 1977) which correlated with the rotation of the sun as well as
sunspot activity (Becker and Gerisch, 1973).
Unnaturally high levels of magnetism. higher than the geomagnetic field, are
often utilized in biological research. Levengood (1967) concluded that Drosophila pupae
subjected to high magnetic fields exhibited morphogenetic anomalies which were
transmitted for 30 generations. Levengood (1965) and his coworker Shinkle (1962)
observed an increase in the number of progeny per generation in periods of enhanced
solar activity. The effect was more pronounced when the magnet was oriented with its
north pole pointing east and the south pole west than when it was placed perpendicular to
this direction. The effect was greater near the north pole than near the south. These
experiments show the importance of a modulated magnetic field on insects, and in this
case. involving fecundity. Magnetic storms would modulate any EM field in the
environment and Cherneyshev (1966) showed a high correlation between insect activity
to light traps and magnetic storms: The correlation coefficient was an astounding 0.926
after accounting for the usual factors, such as temperature, pressure, and humidity.
A permanent magnetic field of 320 millitesla (mT) which is about 10,000 x higher
than the earth's field, was used in an adult emergence study involving the beetle,
Tenebrio molitor (Prolic and Nenadovic, 1995). These investigators found that pupal
metamorphosis into adults was more rapid in the presence of a magnetic field, resulting in
a 14% reduction in eclosion time.
Generally however, high magnetic fields were found to have less effect upon
organisms than low magnetic fields as reviewed in the book Electromagnetic Fields and
LiJe by Presman (1970). One study involving insects showed that low levels of magnetic
fields of 3000 to 4400 Oe (Oersteds) led to genetic changes in Drosophila (Mulay. 1964)
while Reischer (1964) found that higher field strengthh had no effect.
I have just mentioned that the termite, Heterotermes indicola, was discovered by
Giinther Becker to be influenced by the magnetic field produced by the hot water heater
in his laboratory (Becker, 1989) which was 2 m away from the experimental set-up. This
distance was not unprecedented since as long ago as 1900, Danilevskii (quoted in
Presman, 1970) detected the excitation of a frog nerve situated at a distance of several
meters from an EM source (a spark gap). Becker (1971) determined that these termites
can build horizontal galleries that follow the main directions of the geomagnetic field,
and that many insects including cockchafers, bees, crickets, wingless termites, and many
flies are capable of such orientation as well (Becker, 1963a,b)
External fields and their influence upon insects were discussed above. However,
since all live animals produce an electromagnetic field, (some refer to this as an aura) the
question of whether other animals are capable of detecting these fields is of profound
scientific interest. These ultra-weak fields exist in the space proximal to a living
organism (Zimmerman and Rogers, 1989) and extend outward in vanishingly small
intensities to infinity (which is theoretically detectable assuming highly sensitive
equipment is used). Sharks and their relatives and even the platypus detect
extraordinarily faint electromagnetic fields that their animal prey produce (Gregory.
1991). An important question to ask is, "If detection is possible, will this information be
used for communicating?"
Becker (1977a) has shown that termites are capable of detecting large numbers of
their own by way of a physical field that is collectively produced by groups. He has
named this physical field a "biofield". The larger the group, the greater the distance the
effect is observed. The building of vertical galleries by termites is suppressed in the
proximity of large groups of termites (Becker, 1976c, 1977b). He has explained the
biofield as not stemming from any static electric fields, since the experiments were
conducted under the naturally high humid conditions termites are generally found in.
Instead, he suggested that these may be alternating electric fields (Becker, 1977b). This
conclusion was apparently reached from two lines of evidence. The first is that termites
can be directionally influenced by artificial alternating electric fields of low energy
(Becker, 1977a) and secondly, by the work of Ulrich Warnke who only two years earlier
demonstrated that alternating electric fields produced by flying bees are perceived by
other individuals (Warnke, 1975). Direct evidence came for Becker when the effect was
completely suppressed by the addition of 5-mm-thick aluminum plates, one of which was
placed under all containers and the metal grounded (Becker, 1977a).
Groups of 500 individuals produced biofields detectable up to 4 cm away, thus
inhibiting gallery building in the direction of the biofield (Becker, 1989). When 250
individual termites were tested, the response was very weak at 4 cm, but 500 termites
showed no response to their own. when the distance was increased to 6 cm. The
phenomenon that termites produce a larger biofield the larger the group suggests some
form of synergism or interaction, and this interaction may very well be electromagnetic in
nature since EM fields possess the property of falling off by a factor of four as the
distance is doubled (inverse square law). Tunnel building at the periphery of a termite
colony will help to expand the colony and thus improve resource gathering. The
biological importance of detecting their own biofields so as not to build tunnels in the
center of the colony but rather at the periphery most certainly is related to resource
gathering (Becker, 1977b).
In order to test the strength of this response, experiments with competing
variables were designed. The biofields produced by 750 or more termites are stronger
than the alternating magnetic field produced by the electric heater in the room. The fields
produced by 400 or less termites, however, are weaker than the magnetic field at a
distance of about 2 m from its source, but slightly stronger at a distance of 4 m from the
heater. Termites were found to respond to fields produced by species from other families
of Isoptera, but not insects from even related orders, such as Blattaria (Blattoidea).
Additionally, the reaction of termites to physical fields may only be observed when all
other factors are carefully controlled (Becker, 1977c).
Many individuals with their own biofield may not add more energy to the group,
only more units of energy. The intensity of energy from the group might remain the
same. Additive effects may have something to do with their orientational ability. A
correlate is found in most birds, especially the migratory species. Individual birds have
relatively low orientational ability, while the power of the community in this respect is
very high (Naumov and Il'ichev, 1965). These two researchers wrote "The community in
this case frequently emerges as a mediator between the individual and various
environmental factors, like a whole "organism" with interdependent interconnections."
Both of these studies are examples of electromagnetic bio-information, and a fascinating
book with the same title reviews and discusses the literature on this with wonderful
insight (see list of references).
One of the strangest cases of electromagnetic communication possibly involving
biofields also involves termites but of an unknown species. In 1937, Eugene Marais
described a peculiar behavior of these termites in their underground home which was
paraphrased by Callahan (1971)
The cell of the queen termite was encircled by a ring of soldier termites.
The soldiers were equally spaced; half standing on the floor of the queen's
chamber in the area of a half circle facing the queen, and the remaining
soldiers hung upside-down from the chamber roof around the other half of
the circle. All their heads faced directly toward the magnetic north.
Marais concluded that this formation was not a guard ring about the queen
because he could not stir up the strange bodyguards to attack. What then
was their function? While Marias was observing them, a large piece of
clay fell from the roof of the queen cell and dealt the queen a hard blow;
she began moving her head from side to side Immediately, the circle of
bodyguards broke up and wandered around aimlessly. All the workers
even in the most distant chambers of the colony, ceased work and
swarmed into the palace cell. Soldiers and workers in the most remote
parts of the colony gathered in excitement. Slowly the queen recovered,
ceased the rhythmic movement of her head, and the colony returned to
normal. The soldiers replaced themselves in a circle, and the workers in
the remote chambers proceeded back to work. Marais concluded that the
strange circle of soldiers was a link between the brain of the queen and the
colony and carried the influence of the queen to all parts of the colony.
Magnetic field detection
The detection of magnetic fields by an organism is not completely understood, but
this lack of knowledge has led to extremely innovative thinking in the development of
hypotheses. Seven effects of magnetic fields on organisms were listed by Barnothy
(1969) in her book Biological Effects of Magnetic Fields and they are:
1. The existence of transient free radicals which interact with the magnetic field.
2. A change in the rate or mechanism of diffusion across a membrane.
3. Semiconductor effects which would be influenced by the applied field.
4. A change in the rate of production of hormone secretion, for example, oxidative
processes may be altered, influencing the oxidation rate of unsaturated
5. A distortion of the bond angles via paramagnetic molecules which change the
fit between enzyme and substrate.
6. A change in rotational polarization of molecules with specific reactive sites.
7. A change in the rate of proton tunneling in DNA molecules caused by the
applied magnetic field.
The majority of chemical reactions involve molecules, free radicals, and coenzymes, the
latter being mostly bound to metals. Since these can change their character and direction
in a magnetic field (Prolic and Nenadovic, 1995), the striking conclusion to be reached is
that a magnetic field will.influence almost any biochemical reaction.
Further, a magnetic field may be able to influence almost any physiological
mechanism partially due to their strong dependence on biochemical reactions. An
external magnetic field may be transmitted by the neuro-endocrine system, but indirectly
so. The data obtained by Blackmann (1994), along with his colleague, Most, in 1993,
indicated that the information may start with the Ca" ion, at the neural cell membranes.
The calcium ion in turn regulates the secretion of neural hormones reaching the effector
glands and tissues via neurosecretory pathways. The influence of the magnetic field then
would have indirectly influenced many different sites in the body.
The two simplest and most straightforward theories as to how animals detect
magnetic fields were given by Jungerman and Rosenblum in 1980. They are the
mechanical detection of a torque on a magnetic material or the detection of an
electromotive force generated in a moving conductor (i.e. the neuron). The latter is called
"magnetic induction". Based upon theory alone, these two researchers concluded that a
magnetic detection system using induction is unlikely for animals in flight.
The detection of weak magnetic fields has long been a mystery to scientists. How
animals can orient to the geomagnetic field, at only 0.5 gauss, is amazing in and of itself.
(This fact finds particular fascination in man, since we have no conscious awareness of
the earth's magnetic field.) However, modulating the geomagnetic field can help make
both the field and the modulating wave more easily detectable. According to
measurements taken by Cohen (1975) the strongest magnetic fields from the human body
emanate from the heart, and these fluctuating fields measure only 1 x 10'6 gauss in normal
subjects. Some very large biomagnetic fields are created by unnatural circumstances such
as lung contaminants which are still about 50,000 x weaker than the geomagnetic field
(Zimmerman and Rogers, 1989). Can insects respond to these low level magnetic fields?
If there is sufficient time to carry out a special analysis on a signal, it is at least
technically possible for man to recover signals with a level far below the interference
limit (Konig, 1989). A comparable situation is also conceivable from the perspective of a
biological organism. Ulrich Warnke has studied for years the effects of alternating
magnetic fields upon humans and has obtained results suggesting that effects may be
observed by forces as much as 8 levels of magnitude lower than forces caused by thermic
noise (Warnke, 1989b).
By and large, biomagnetic experiments, especially involving low-level fields,
indicate that the biological effect of the magnetic field is not instantaneous, but requires a
continuous exposure to the magnetic field for a critical length of time in order for the
effect to be observed (Abler, 1969). This strongly suggests that neuronal spikes do not
occur in quick response to field exposure, and that electrophysiological techniques would
not be very useful in measuring a response of this type.
Even though some interaction probably exists between the CNS and external
magnetic fields (Becker, 1969), the effect is likely not on the action potential since no
effect on a variety of action potential parameters occurred with exposure to high strength
fields (Liberman et al., 1959). Instead of the usual increase in spike (action potential)
rate, Russell (1969) reported a 17-27% inhibition in firing rates in the subesophageal
ganglion of the cockroach, Periplaneta americana, when exposed to a constant magnetic
field of 6600 Oe.
Most of the established biomagnetic effects have been observed in vivo. Since
very small energy is imparted on a biological system by a magnetic field, it seems likely
that a built-in amplification system may occur in the organism (Bamothy, 1969). Smith
(1989) and Kroy (1989) reported the possibility that the entire organism may be
responding to the magnetic field, or the total mass of the connective tissue, and not just a
part of the organism. Since all organisms have an electromagnetic aura about them, a
magnetic field would certainly affect this aura. If the aura were affected, either g, od or
bad, then there is always the possibility that the organism may be able to detect the
magnetic field simply by virtue of its interaction upon the homeostatic mechanisms,
which collectively contribute to a healthy aura. Therefore, if the electrostatic charges of
an animal, especially a flying animal, come into a complex interaction with the terrestrial
magnetic field (a much greater field intensity), and if the resulting nuances are of use to
the animal, then magnetic field orientation can occur (Warnke, 1989a). A special
magnetic sense would thus be rendered unnecessary.
Magnetic fields, unlike electrical fields, are able to penetrate deeply into
biological tissue. Electrical currents have difficulty in passing through the relatively low-
conductivity (human) skull, whereas magnetic fields do so easily (Zimmerman and
Rogers, 1989). For this reason, any magnetic receptors, if present, need not be located on
the outside of the body (Warnke and Popp. 1989). The central nervous system of humans
is predominantly internal and can be influenced by magnetic fields with frequencies of
extremely narrow bandwidths (1.6-3.6, 7.8, 10.8, 11.4 Hz) and low amplitudes (Maxey,
The phenomena that all fish are surrounded by individual electromagnetic auras is
well known. These auras take on the form of a dipolar continuous current field, where
the mouth is negative and the gills are largely positive. This EM field is modulated by
mechanical breathing. This modulated field is easily detectable to sharks, rays, and
sturgeons, as signs of prey. Discrete receptors are implicated in this case, and they are
called the ampullaee of Lorenzini".
Identifiable receptors exist in some organisms, as I have already discussed with
the bacteria and honeybees. However, one cannot assume that these receptors will react
and convert the message in the same way. Bacteria responsive to the geomagnetic field
contain novel structured particles, rich in iron, within intracytoplasmic membrane
vesicles (Blakemore, 1975). The honeybees, on the other hand, contain magnetite in their
abdomen (Gould et al., 1978). Although both iron and magnetite do respond to magnetic
fields, the system in bacteria is likely different from that in honeybees since the physical
make-up of the receptors differs as well as the magnetic substance utilized.
Ferritin, a protein complex of iron, contains about 23% by weight of the elemental
metal (Senftle and Hambright, 1969) and is relatively paramagnetic (a weak attraction
toward a magnet). It plays an important function in both plants and animals (Neurath,
1969), however, it is not known whether or not this ubiquitous substance plays a role in
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