SU. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY-BULLETIN No. 121.
L 0. HOWARD, Entomologist and Chief of Bureau.
THE BEHAVIOR OF THE HONEY BEE
IN POLLEN COLLECTING.
D. B. CASTEEL, Pi. D.,
Collaborator and Adjunct Professor of Zoology,
University of Texas.
ISSUED DECEMBER 31, 1912.
GOVERNMENT PRINTING OFFICE.
BUREAU OF ENTOMOLOGY.
L. 0. HOWARD, Entomologist and Chief of Bureau.
C. L. MARLATT, Entomologist and Acting Chief in Absence of Chief. l
R. S. CLIFTON, Executive Assistant.
W. F. TASTET, Chief Clerk. I
F. H. CHITTENDEN, in charge of truck crop and stored product insect investigations. '
A. D. HOPKINS, in charge of forest insect investigations. .
W. D. HUNTER, in charge of southern field crop insect investigations. ,
F. M. WEBSTER, in charge of cereal and forage insect investigations. ,
A. L. QUAINTANCE, in charge of deciduous fruit insect investigations. ,,
E. F. PHTTLTPS, in charge of bee culture.
D. M. ROGERS, in charge of preventing spread of moths, field work. :
ROLLA P. CUTRIE, in charge of editorial work. 3
MABEL COLCORD, in charge of library.
INVESTIGATIONS IN BEE CULTURE.
E. F. PHILLIPS, in charge.
G. F. WHITE, J. A. NELSON, eo-perts.
G. S. DEMUTH, A. H. McCRAY, N. E. MCINDOO, apicultural assistants.
PEARLE H. GARRISON, preparator.
D. B. CASTEEL, collaborator.
LETTER OF TRANSMITTAL.
U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF ENTOMOLOGY,
Washington, D. C., September 23, 1912.
Sin: I have the honor to transmit herewith a manuscript entitled
"The Behavior of the Honey Bee in Pollen Collecting," by Dr. Dana
B. Casteel, of this bureau. The value of the honey bee in cross pol-
linating the flowers of fruit trees makes it desirable that exact infor-
mation be available concerning the actions of the bee when gathering
and manipulating the pollen. The results recorded in this manu-
script are also of value as studies in the behavior of the bee and will
prove interesting and valuable to the bee keeper. The work here
recorded was done by Dr. Casteel during the summers of 1911 and
1912 at the apiary of this bureau.
I recommend that this manuscript be published as Bulletin No. 121
of the Bureau of Entomology.
Respectfully, L. 0. HOWARD,
Entomologist and Chief of Bureau.
Hon. JAMES WILSON,
Secretary of Agriculture.
Introduction .............................................................. 7
The structures concerned in the manipulation of pollen---------------------...................... 7
The pollen supply....................................................-----------------------------------------------..... 10
General statement of the pollen-collecting process............................ ------------------------11
Action of the forelegs and mouthparts ....................................... 13
Action of the middle legs ................................................... 14
Action of the hind legs------..........------------.....-----------...---------------....... 16
Additional details of the basket-loading process................................ 18
Pollen moistening........................... ..............................------------------------------------------------ 22
Storing pollen in the hive .................................................. 29
Summary- ............----.......-..............---------................................. 31
Bibliography .....................................................---------------------------------------------------....... 33
Index ...................................................................... 35
FIG. 1. Left foreleg of a worker bee........................................
2. Left middle leg of a worker bee....................................
3. Outer surface of the left hind leg of a worker bee....................
4. Inner surface of the left hind leg of a worker bee....................
5. A flying bee, showing the manner in which the forelegs and middle legs
6. A bee upon the wing, showing the position of the middle legs when they
touch and pat down the pollen masses .............................
7. A bee upon the wing, showing the manner in which the hind legs are
held during the basket-loading process .............................
8. The left hind legs of worker bees, showing the manner in which'pollen
enters the basket ..................................................
9. Inner surface of the right hind leg of a worker bee which bears a com-
plete load of pollen..............................................
... .. 7 .. . ..... *M|i
THE BEHAVIOR OF THE HONEY BEE IN POLLEN COLLECTING.
While working upon the problem of wax-scale manipulation dur-
ing the summer of 1911 the writer became convinced that the so-
called wax shears or pinchers of the worker honey bee have nothing
whatever to do with the extraction of the wax scales from their
pockets, but rather that they are organs used in loading the pollen
from the pollen combs of the hind legs into the corbicule or pollen
baskets (Casteel, 1912). Further observations made at that time dis-
closed the exact method by which the hind legs are instrumental in
the pollen-loading process and also the way in which the middle legs
aid the hind legs in patting down the pollen masses. During the
summer of 1912 additional information was secured, more particu-
larly that relating to the manner in which pollen is collected upon
Sthe body and legs of the bee, how it is transferred to the hind legs,
how it is moistened, and finally the method by which it is stored in
the hive for future use. In the present paper a complete account will
be given of the history of the pollen from the time it leaves the flower
until it rests within the cells of the hive. The points of more par-
ticular interest in the description of pollen manipulation refer to
(1) the movements concerned in gathering the pollen from the
flowers upon the body and legs, (2) the method by which the baskets
of the hind legs receive the loads which they carry to the hive, and
(3) the manner in which the bee moistens pollen and renders it suf-
ficiently cohesive for packing and transportation.
THE STRUCTURES CONCERNED IN THE MANIPULATION OF
The hairs which cover the body and appendages of the bee are of
the utmost importance in the process of pollen gathering. For the
purposes of this account these hairs may be classified roughly as
(1) branched hairs and (2) unbranched hairs, the latter including
both long, slender hairs and stiff, spinelike structures.
Of these two classes the branched hairs are the more numerous.
They make up the hairy coat of the head, thorax, and abdomen, with
the exception of short. sensory spines, as those found upon the an-
tennar and perhaps elsewhere, and the stiff unbranched hairs which
BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.
cover the surfaces of the compound eyes (Phillips, 1905). BraidudI:
hairs are also found upon the legs; more particularly upon the aq.J
proximal segments. A typical branched hair is composed of a leg.I'l
slender main axis from which spring numerous short lateral barbs. ,
Grains of pollen are caught and held in the angles between the axis.i
and the barbs and between the barbs of contiguous hairs. The J44 1
covering of the body and legs thus serves as a collecting surface upon
which pollen grains are temporarily retained and from which they
are later removed by the combing action of the brushes of the legs.
Although, as above noted, some unbranched hairs are located upon
the body of the bee, they occur in greatest numbers upon the more
distal segments of the appendages. They are quite diverse in fornn
some being extremely long and slender, such as those which curve
over the pollen
Aaftr&i baskets, others
being stout sad
stiff, 'as thoe'0
which form the
-- collecting brushes
and the pecten
At J 'parts of the bee
C--'--' iare also essentil
Lf tto the proper .el-
_BrashA on^^p election of pollen.
T h e mandibles
Share used to scraMpe
over the anthers
FIG. 1.-Left foreleg of a worker bee. (Original.) of flowers, an
considerable pollen adheres to them and is later removed. The same
is true of the maxillae and tongue. From the mouth comes the fluid
by which the pollen grains are moistened.
The legs of the worker bee are especially adapted for pollen gath-
ering. Each leg bears a collecting brush, composed of stiff, un-
branched hairs set closely together. These brushes are located upon
the first or most proximal tarsal segment of the legs, known techni-
cally as the palmme of the forelegs and as the plantam of the middle
and hind pair. The brush of the foreleg is elongated and of slight
width (fig. 1), that of the middle leg broad and flat (fig. 2), while
the brush upon the plant of the hind leg is the broadest of all, adi
is qlso the most highly specialized. In addition to these well-marked
brushes, the distal ends of the tibiae of the fore and middle legs bear
many stiff hairs, which function as pollen collectors, and the distal
tarsal joints of all legs bear similar structures.
THE STRUCTURES CONCERNED.
i The tibia and the plant of the hind leg of the worker bee are
* greatly flattened. (See figs. 3, 4.) The outer surface of the tibia is
S marked by an elongated depression, deepest at its distal end, and
bounded laterally by elevated margins. From the lateral boundaries
of this depression spring many long hairs, some of which arch over
the concave outer surface of the tibia and thus form a kind of recep-
tacle or basket to which the name corbicula or pollen-basket is given.
The lower or distal end of the tibia articulates at its anterior edge with
the plant. The remaining portion of this end of the tibia is flat-
tened and slightly concave, its
surface sloping upward from m
the inner to the outer surface _-."
of the limb. Along the inner
edge of this surface runs a row w_ e.
of short, stiff, backwardly di-
rected spines, from 15 to 21 in
number, which form the pec-
ten or comb of the tibia. The
lateral edge of this area forms
the lower boundary of the .
corbicular depression and is
marked by a row of very fine %
hairs which branch at their
free ends. Immediately above \\ -- i
these hairs, springing from the
floor of the corbicula, are found / -SAr
7 or 8 minute spines, and above R fa
them one long hair which Am 01IPRe
reaches out over the lower edge
of the basket.
The broad, flat plant (meta-
tarsus or proximal tarsal seg-
ment of thehind leg) is marked
on its inner surface by several
rows of stiff, distally directed Fi.. 2.-Left middle leg of a worker bee.
spines which form the pollen oginal.)
combs. About 12 of these transverse rows may be distinguished,
although some of them are not complete. The most distal row, which
projects beyond the edge of the plant, is composed of very strong,
stiff spines which function in the removal of the wax scales (Casteel,
1912). The upper or proximal end of the plant is flattened and pro-
jects in a posterior direction to form the auricle. The surface of the
auricle is marked with short, blunt spines, pyramidal in form, and a
fringe of fine hairs with branching ends extends along its lateral edge.
This surface slopes upward and outward.
THE POLLEN SUPPLY.
When bees collect pollen from flowers they mly be engtgeid At
occupation alone or may combine it with nectar gathering,.h.. i!
some flowers the bees take only nectar, from others only I '.
third class of-flowers fur.iA j
an available supply of -boAo. :$1
eZ ^ ~these substances. But :':'!"t
!_-Amur where both pollen and i*S ."'.
llA^ are obtainable a bee 'ina"i
wr ^^^gather nectar and disr* i41: ''
'l i ~the pollen. This is well Hil- !
kt '-' treated by the case of wlihft4
f 'clover. If bees are wathM 3'j
_4 Ma;^^ while working upon" W H
^e -4.^ flowers, the observer will soon
l Eli 'perceive some which bear'- :V:1
len masses upon their hinf i
4 ~legs, while others will continuA
(brbi'lcz to visit flower after fIMMl ,
UHdipping into the blossoms aM
securing a plentiful supply'f i
nectar, yet entirely neglecting
W \'- ^ The supply of pollen whiA
,\ is available for the bees va ies
f I greatly among different frow "
f' !" ~ ers. Some furnish an abunL n
d 1" dant amount and present it h
i the bee in such a way thit
little difficulty is experienced
i! iin quickly securing an ample .,
,l ~load, while others furnish t bN
f|^little. When flowers are smtll!
f^, ~and when the bee approachfis i
aj them from above, little, if aily,
^y pollen is scattered over -thel
j ~bee's body, all that it acqduiie i.
being first collected upon tih &
E~ ~mouth and neighboring part.S
FMG. 3.-Outer surface of the left hind leg of a Very different conditions ztiI
worker bee. (Original.) 1 *
met with when bees visit sd"m lJ
plants as corn and ragweed. The flowers of these plants are penh'..k
and possess an abundant supply of pollen, which falls in Showers o
the bodies of the bees as they crawl beneath the blossoms. d .
GENERAL STATEMENT OF PROCESS.
supply of pollen which lodges upon the body of the bee will thus
differ considerably in amount, depending upon the type of flower
from which the bee is collecting, and the same is true regarding the
location upon the body of a bee of pollen grains which are available
for storage in the baskets. i
Moreover, the movements
concerned in the collection r, t l wur
of the pollen from the va- ""
rious body parts of the '
bee upon which it lodges \
will differ somewhat in IP.
the two cases, since a ia-
widely scattered supply \
requires for its collection .'-.\ P An '
additional m o v e m e n t s
somewhat, similar in na- Posterir:e
ture to those which the 'L5$ii
bee employs in cleaning I-vN
the hairs which cover its ,
body. Pecin A i '44
GENERAL STATEMENT '
OP THE POLLEN-COL- A 'urwle--
A very complete knowl-
edge of the pollen-gather- P
ing behavior of the worker onllina(m
honey bee may be obtained
by a study of the actions
of bees which are' work-
ing upon a plant which
yields pollen in abun-
dance. Sweet corn is an
ideal plant for this pur-
pose, and it will be used
as a basis for the descrip-
tion which follows.
In attempting to out-
line the method by which FIG. 4.-Inner surface of the left hind leg of a
worker bee. (Original)
pollen is manipulated the
writer wishes it to be understood that he is recounting that which
he has seen and that the description is not necessarily complete,
although he is of the opinion that it is very nearly so. The move-
ments of the legs and of the mouthparts are so rapid and so many
12 BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.
members are in action at once that it is impossible for l e &:daii
follow all at the same time. However, long-continuedh obaeI:
assisted by the study of instantaneous photographs, gives enf*ii .l
that the statements recorded are accurate, although some nw *,imet:'j1
may have escaped notice. i '?liN*::i
To obtain pollen from corn the bee must find a tassel in the ight N&
stage of ripeness, with flowers open and stamens hanging frost thW W I
The bee alights upon a spike and crawls along it, clinging t he1
pendent anthers. It crawls over the anthers, going from one flwe' *l
to another along the spike, being all the while busily engaged in thb 1.
task of obtaining pollen. This reaches its body in several ways.
As the bee moves over the anthers it uses its mandibles and tongi k |
biting the anthers and licking them and securing a consideable
amount of pollen upon these parts. This pollen becomes moist und
sticky, since it is mingled with fluid from the mouth. A considerable
amount of pollen is dislodged from the anthers as the bee moves .fl'
them. All of the legs receive a supply of this free pollen and nuA4 '
adheres to the hairs which cover the body, more particularly to thos6
upon the ventral surface. This free pollen is dry and powdery ud
is very different in appearance from the moist pollen masses Wit "
which the bee returns to the hive. Before the return journey this
pollen must be transferred to the baskets and securely packed in them.
After the bee has traversed a few flowers along the spike and i.as
become well supplied with free pollen it begins to collect it from its
body, head, and forward appendages and to transfer it to the pos-
terior pair of legs. This may be accomplished while the bee is
resting upon the flower or while it is hovering in the air before
seeking additional pollen. It is probably more thoroughly and rap*
idly accomplished while the bee is in the air, since all of the legs are
then free to function in the gathering process. '
If the collecting bee is seized with forceps and examined after it
has crawled over the stamens of a few flowers of the corn-, its leo
and the ventral surface of its body are found to be thickly powdered
over with pollen. If the bee hovers in the air for a few momefti
and is then examined very little pollen is found upon the body e.re
upon the legs, except the masses within the pollen baskets. While in
the air it has accomplished the work of collecting some of the soat= *
tered grains and of storing them in the baskets, while others have 2
been brushed from the body.
In attempting to describe the movements by which this result Aisg
accomplished it will be best first to sketch briefly the r6les oftin.:
three pairs of legs. They are as follows: i N|
(a) The first pair of legs remove scattered pollen from the hA .t*
and the region of the neck, and the pollen that has been moisteniu
by fluid substances from the mouth. N
ACTION OF FORELEGS AND MOUTHPARTS.
S(b) The second pair of legs remove scattered pollen from the
S thorax, more particularly from the ventral region; and they re-
ceived the pollen that has been collected by the first pair of legs.
S(c) The third pair of legs collect a little of the scattered pollen
from the abdomen and they receive pollen that has been collected
by the second pair. Nearly all of this pollen is collected by the
pollen combs of the hind legs, and is transferred from the combs to
the pollen baskets or corbiculse in a manner to be described later.
It will thus be seen that the manipulation of pollen is a succes-
sive process, and that most of the pollen at least passes backward
from the point where it happens to touch the bee until it finally
reaches the corbiculhe or is accidentally dislodged and falls from the
rapidly moving limbs.
ACTION OF THE FORELEGS AND MOUTHPARTS.
Although the pollen of some plants appears to be somewhat sticky,
it may be stated that as a general rule pollen can not be successfully
manipulated and packed in the baskets without the addition of some
fluid substance, preferably a fluid which will cause the grains to
cohere. This fluid, the nature of which will be considered later,
comes from the mouth of the bee, and is added to the pollen which
is collected by the mouthparts and to that which is brought into con-
tact with the protruding tongue and maxillae, and, as will appear,
this fluid also becomes more generally distributed upon the legs and
upon the ventral surface of the collecting bee.
When a bee is collecting from the flowers of corn the mandibles are
actively engaged in seizing, biting, and scraping the anthers as the
bee crawls over the pendent stamens. Usually, but not always, the
tongue is protruded and wipes over the stamens, collecting pollen
and moistening the grains thus secured. Some of the pollen may
possibly be taken into the mouth. MAll of the pollen which comes in
P contact with the mouthparts is thoroughly moistened, receiving more
fluid than is necessary for rendering the grains cohesive. This
exceedingly wet pollen is removed from the mouthparts by the fore-
legs (fig. 5), and probably the middle legs also secure a little of it
S directly, since they sometimes brush over the lower surface of the
S face and the.mouth. In addition to removing the very moist pollen
S from the mouth the forelegs also execute cleansing movements over
: the sides of the head and neck and the anterior region of the thorax,
: thereby collecting upon their brushes a considerable amount of pollen
S which has fallen directly upon these regions, and this is added to the
pollen moistened from the mouth, thereby becoming moist by contact.
i The brushes of the forelegs also come in contact with the anterior
breast region, and the hairs which cover this area become moist with
S the sticky exudation which the forelegs have acquired in the process
S of .wiping pollen from the tongue, maxilla, and mandibles.
14 BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.
ACTION OP THE MIDDLE LEGS. ..i...,i|
m .. ... ..=.
The middle legs are used to collect the pollen gatheed.. ." ..
forelegs and mouthparts, to remove free pollen from the tht
region, and to transport their load of pollen to the hind legs, p ' .
most of it upon the pollen combs of these legs, although a
amount is directly added to the pollen masses in the corbiculie. |
of the pollen of the middle legs is gathered upon the conspi... :i
brushes of the first tarsal segments or planted of these legs. .
In taking pollen from a foreleg the middle leg of the same side.is ... j
tended in a forward direction and is either grasped by the flexed f.d' .
leg or rubbed over the foreleg as it is bent downward and backwaiA i
In the former movement the foreleg flexes sharply upon itself until'.
.^ - -r- -^.' :': i [*
FiG. 5.-A flying bee, showing the manner in which the forelegs and middle legs m i.
late pollen. The forelegs are removing wet pollen from the mouthparts and face. ThaI
middle leg of the right side is transferring the pollen upon its brush to the pleUtk
combs of the left hind plant. A small amount of pollen has already been placed IJ
the baskets. (Original.)
the tarsal brush and coxa nearly meet. The collecting brush of th..
middle leg is now thrust in between the tarsus and coxa of the for *I
leg and wipes off some of the pollen from the foreleg brush.
middle leg brush is then raised and combs down over the flexed To'r
leg, thus removing additional pollen from the outer surface of tJI4
leg. The middle leg also at times reaches far forward, stroking down f
over the foreleg before it is entirely flexed and apparently corZA*| .:...
over with its tarsal brush tLe face and mouthpartp thems4WA4
V : ,.. ... .
When the middle leg reaches forward to execute any of the ab
movements the direction of the stroke is outward, forward, and' te ojr.
back toward the body, the action ending with the brush of the eg'
contact with the long hairs of the breast and with those which otspriW or'
leg nd ipe of som ofthepolen fom he oreeg bush : ,F
ACTION OF MIDDLE LEGS..
from the proximal segments of the forelegs (coxa, trochanter,
femur). As a result of the oft-repeated contact of the brushes of
the middle and forelegs with the breast, the long, branched hairs
which cover this region become quite moist and sticky, since the
brushes of these two pair of legs are wet and the pollen which they
bear possesses a superabundance of the moistening fluid. Any dry
pollen which passes over this region and touches these hairs receives
moisture by contact with them. This is particularly true of the free
dry pollen which the middle pair of legs collect by combing over the
sides of the thorax.
The pollen upon the middle legs is transferred to the hind legs in
at least two ways. By far the larger amount is deposited upon the
pollen combs which lie on the inner surfaces of the planted of the
FIG. 6.-A bee upon the wing, showing the position of the middle legs when they touch
and pat down the pollen masses. A very slight amount of pollen reaches the corbicula
through this movement. (Original.)
hind legs. To accomplish this a middle leg is placed between the
planted of the two hind legs, which are brought together so as to grasp
the brush of the middle leg, pressing it closely between them, but
allowing it to be drawn toward the body between the pollen combs
of the two hind legs. (See fig. 5.) This action results in the trans-
ference of the pollen from the middle-leg brush to the pollen combs
of the hind leg of the opposite side, since the combs of that leg scrape
over the pollen-laden brush of the middle leg. This action may take
place while the bee is on the wing or before it leaves the flower.
The middle legs place a relatively small amount of pollen directly
upon the pollen masses in the corbiculae. This is accomplished when
the brushes of the middle legs are used to pat down the pollen masses
and to render them more compact. (See fig. 6.) The legs are used
16 BEHAVIOR OF HONEY BEE IN POLLEN OOLIL, TING ...;:
.... ::* '**^ii~iilllll
for this purpose quite often during the process of loading tbh ....:`' .....l.
and a small amount of pollen is incidentally added to *thei f...
when the brushes come into contact with them. A misin "
of this action has led some observers into the erroneous
all or nearly all of the corbicular pollen is scraped from ti
leg brushes by the hairs which fringe the sides of the bagejtgp. i
middle legs do not scrape across the baskets, but merely pt qq'1
ward upon the pollen which is there accumulating. 4 ....; .
It is also possible that, in transferring pollen from the mid4J .:ij'
of one side to the plant of the opposite hind leg, the midWe]sIl
brush may touch and rub over the pecten of the hind leg Pa t :ws
directly place some of its pollen behind the pecten spines. u aL'Il
result is, however, very doubtful. iihi
ACTION OF THE HIND LEGS.
The middle legs contribute the major portion of the pollenW h4,inch
reaches the hind legs, and all of it in cases where all of the polk 'i
first reaches the bee in the region of the mouth. However, wbhen' !||
much pollen falls upon the body of the bee the hind legs collect a ::i
little of it directly, for it falls upon their brushes and is colle &
upon them when these legs execute cleansing movements to remove :
it from the ventral surface and sides of the abdomen. All of the .
pollen which reaches the corbiculae, with the exception of the small
amount placed there by the middle legs when they pat down the
pollen masses, passes first to the pollen combs of the planted.
When in the act of loading pollen from the plantar brushes to the
corbiculhe the two hind legs hang beneath the abdomen with the tibio-
femoral joints well drawn up toward the body. (See fig. 7.) The
two plantae lie close together with their inner surfaces nearly parallel
to each other, but not quite, since they diverge slightly at their distal A
ends. The pollen combs of one leg are in contact with the pecten i
comb of the opposite leg. If pollen is to be transferred from tie
right plant to the left basket, the right plant is drawn upward in i
such a manner that the pollen combs of the right leg scrape ovq
the pecten spines, of the left. By this action some of the polle
removed from the right plantar combs and is caught upon the ojv
surfaces of the pecten spines of the left leg. ,,,
This pollen now lies against the pecten and upon the flattenS
distal end of the left tibia. At this moment the plant of thel :'A
leg is flexed slightly, thus elevating the auricle and bringing the a$t. ,
cular surface into contact with the pollen which the pecten ham jv.b:w
received. By this action the pollen is squeezed between the ead o:Mf :*
tibia and the surface of the auricle and is forced upward against the :i
distal end of the tibia and on outward into contact with the ,pellii
mass accumulating in the corbicula. As this act, by wthichftsiIjS
ACTION OF HIND LEGS. 17
basket receives a small contribution of pollen, is being completed, the
right leg is lowered and the pecten of this leg is brought into contact
|! with the pollen combs of the left plant, over which they scrape as
S the left leg is raised, thus depositing. pollen upon the lateral surfaces
S of the pecten spines of the right leg. (See fig. 7.)
S. Right and left baskets thus receive alternately successive contribu-
tions of pollen from the plant of the opposite leg. These loading
movements are executed with great rapidity, the legs rising and fall-
ing with a pump-like motion. A very small amount of pollen is
loaded at each stroke and many strokes are required to load the
: If one attempts to obtain, from the literature of apiculture and
Zoology, a knowledge of the method by which the pollen baskets
Ni. "" . "2 ',
FIG. 7.-A bee upon the wing, showing the manner in which the hind legs are held during
II:the basket-loading- process. Pollen Is being scraped by the pecten spines of the right
y:leg from the pollen combs of the left hind plant. (Original.)
||| themselves are loaded, he is immediately confused by the diversity of
I: the .accounts available. The average textbook of zoology follows
.V, closely Cheshire's (1886) description in which he says that "the legs
Hare crossed, and the metatarsus naturally scrapes its comb face on the
II: upper edge of the opposite tibia in the direction from the base of the
Ipcombs toward their tips. These upper hairs ***are nearly
straight, and pass between the comb teeth. The pollen, as removed,
11, is caught by the bent-over hairs, and secured. Each scrape adds to
^:i* the-mass, until the face of th-e joint is more than covered, and the
hairs just embrace the pellet." Franz (1906) states that (translated)
Ij lthe final loading of the baskets is accomplished by the crossing over
^I" of the hind-tarsal segments, which rub and press upon each other."
Many other observers and textbook writers evidently believed that
the hind legs were crossed in the loading process.
; Fm(. 7.--A bee upon the wing, showing the manner in which the hind legs are held during
the basket-loading process. Pollen Is being scraped by the pecten spines of the right
i,,: leg from the pollen combs of the left hind plant. (Original.)
themselves are loaded, he is immediately confused by the diversity of
: the ,accounts available. The average textbook of zoology follows
closely Cheshire's (1886) description in which he says that "the legs
i,* are crossed, and the metatarsus naturally scrapes its comb face on the
upper edge of the opposite tibia in the direction from the base of the
S combs toward their tips. These upper hairs are nearly
li',!, straight, and pass between the comb teeth. The pollen, as removed,
S is caught by the bent-over hairs, and secured. Each scrape adds to
i the mass, until the face of the joint is more than covered, and the
u hairs just embrace the pellet." Franz (1906O) states that (rnltd
i, "the final loading of the baskets is accomplished by the crossing over
ofi..... theind-tarsal segments, which rub and press upon each other."
i,, Many other observers and textbook writers evidently believed that
Jit* the hind legs were crossed in the loading process.
On the other hand, it is believed by some that the middlehtA.
directly instrumental in filling the baskets. this method i.'
in the following quotation from Fleischmann and Zander l1
The second pair of legs transfer the pollen to the hind legs, whete .it
heaped up in the pollen masses. The tibia of each hind leg is depre ssed h..
outer side, and upon the edges of this depression stand two rows of stiff bki:' l
which are bent over the groove. The brushes of the middle pair of beg A.M
over these hairs, liberating the pollen, which drops into the baskets. ..........
A suggestion of the true method is given by Hommell (IWI LAP:
though his statements are somewhat indefinite. After descrMit aM
the method by which pollen is collected, moistened, and passed to /||
the middle legs he states that (translated) "the middle legs pla&1 '!
their loads upon the pollen combs of the hind legs. There the sticky
pollen is kneaded and is pushed across the pincher (a trawvera`e:i W 1
pince), is broken up into little masses and accumulates within th i$rj
corbicula. In accomplishing this, the legs cross and it is the tarsiiu:;i|
of the right leg which pushes the pollen across the pincher of th jM
left, and reciprocally. The middle legs never function directly ia
loading the baskets, though from time to time their sensitive ea i!
tremities touch the accumulated mass, for the sake of giving assur1;:.;i
ance of its position and size." ,
The recent valuable papers of Sladen (1911, 1912, a, b, c, d, and e) 'iii
who was the first to present a true explanation of the function of
the abdominal scent gland of the bee, give accounts of the process::
by which the pollen baskets are charged, which are in close accord
with the writer's ideas on this subject. It is a pleasure to be able to.:
confirm most of Sladen's observations and conclusions, and weight is' '
added to the probable correctness of the two descriptions and iW.
terpretations of this process by the fact that the writer's studies w -.
the conclusion based upon them were made prior to the appearance i
of Sladen's papers and quite independent of them. His description jU
of the basket-loading process itself is so similar to the writer's.o* M |
that a complete quotation from him is unnecessary. A few differences .
of opinion will, however, be noted while discussing some of the moytf :.* 1:2
ments which the process involves. As will later be noted, our id &is
regarding the question of pollen moistening, collecting, and transl4*4 j',|;
ence are somewhat different. ......... i
ADDITIONAL DETAILS OF THE BASKET-LOADING PROCVIE' 'W-'
:.^.. .' ,, d *:i.^ii
The point at which pollen enters the basket can best be deteu i4.Atc
by examining the corbicule of a bee shortly after it has readid ef
flower and before much pollen has been collected. Withip e.4..i
pollen basket of such a bee is found a small mass of poUlen .whiok. .:;1j
ADDITIONAL DETAILS OF BASKET-LOADING PROCESS.
along the lower or distal margin of the basket. (See fig 8, a.) It is
in this position because it has been scraped from the plant of the
opposite leg by the pecten comb and has been pushed upward past
the entrance of the basket by the continued addition of more from
below, propelled by the successive strokes of the auricle. Closer
FIG. 8.-Camera drawings of the left hind legs of worker bees to show the manner in
which pollen enters the basket, a, Shows a leg taken from a bee which is just begin-
ning to collect. It had crawled (.vir a few flowers and had flown in the air about five
seconds at the time of capture. The pollen mass lies at the entrance of the basket,
covering over the fine hairs which lie along this margin and the seven or eight short
stiff spines which spring from the floor of the corbicula immediately above its lower
edge. As yet the pollen hias not come in contact with the one long hair which rises
from the floor and arches over the entrance. The planta is extended, thus lowering
the auricle; b, represents a slightly later stage, showing the increase of pollen. The
plant is flexed, raising the auricle. The hairs which extend outward and upward from
the lateral edge of the auricle press upon the lower and outer surface of the small
pollen mass, retaining it and guiding it upward into the basket; c, d, represent slightly
later stages in the successive processes by which additional pollen enters the basket.
examination of the region between the pecten and the floor of the
basket itself shows more pollen, which is on its way to join that
already squeezed into the basket.
If the collecting bee is watched for a few moments the increase will
readily be noted and the fact will be established that the accumulat-
ing mass is gradually working upward or proximally from the lower
20 BEHAVIOR OF HONEY BEE IN POLLEBN COLLCTINI .
or distal edge of the corbicula and is slowly covering the floor. I i
receptacle. (See fig. 8, 6, c, and d.) In many intAtwe J
cessive contributions remain for a time fairly separate, t
mass being marked by furrows transverse to the long axis of tntMd
Sladen (1912, b) notes the interesting fact that in those rM
exceptional cases when a bee gathers pollen from more tha p
species of flowers the resulting mass within the corbicula wiMA i".
a stratification parallel to the distal end, a condition which.'i.
result only from the method of loading here indicated. A ....
As the pollen within the basket increases in amount it bulge onu J.
ward, and projects downward below the lower edge of the basket.: t
It is held in position by the long hairs which fringe the lateral::: Asid.
of the basket, and its shape is largely determined by the f of::mfi
these hairs and the direction in which they extend. When the iAket
is fully loaded the mass of pollen extends laterally on both si,4 of:.l
the tibia, but projects much farther on the posterior side, for oN.Mbis
side the bounding row of hairs extends outward, while on the 'atior: .i
edge the hairs are more curved, folding upward and over the b '.. ill..
As the mass increases in thickness by additions from below it is "'
in position by these long hairs which edge the basket. Theyr":j
pushed outward and many of them become partly embedded in *e .e:i
pollen as it is pushed up from below. When the pollen grains e :
small and the whole mass is well moistened the marks made by 9sa0 4.
of the hairs will be seen on the sides of the load. (See fig. : ,Li
These scratches are also transverse in direction and they sho,:::hat $ it
the mass has been increased by additions of pollen pushed upitfrom '
Even a superficial examination of a heavily laden basket showss
the fallacy of the supposition that the long lateral fringing hairs a ,re
used to comb out the pollen from the brushes of either the hinld .
middle legs by the crossing of these legs over the lateral edges of t1he :
baskets. They are far from sufficiently stiff to serve this purpose,
and their position with relation to the completed load shows n- :!i
elusively that they could not be used in the final stages of the loading ,
process, for the pollen mass has completely covered many 0of *tiibm
and its outer surface extends far beyond their ends. They :,,
merely to hold the pollen in place and to allow the load to prWOO:co
beyond the margins of the tibia. ':.. :
The auricle plays a very essential part in the process of loadii
the basket. This structure comprises the whole of the ftteat iji
proximal surface of the plant, except the joint of articulation i
and it extends outward in a posterior direction a little be.yod
remaining plantar edge. The surface of the auricle i's obve re4 M-
with many blunt, short spines and its lateral margin is boundMii
a row of short rather pliable hairs, branched at their ends& ''i
ADDITIONAL DETAILS OF BASKET-LOADING PROCESS. 21
the plant is flexed the auricle is raised and its surface approaches
the distal ezd of the tibia, its inner edge slipping up along the pecten
spines and its outer hairy edge projecting into the opening which
leads to the pollen basket. (See fig. 8, b.) With each upward stroke
of the auricle small masses of pollen which have been scraped from the
plantar combs by the pecten are caught and compressed between the
Spiny surface of the auricle and the surface of the tibia above it.
i The pressure thus exerted forces the pasty pollen outward and up-
ward, since it can not escape past the base of the pecten, and directs
it into the entrance to the corbicula. The outward and upward slant
S of the auricular surface and the projecting hairs with which the outer
edge of We auricle is supplied also aid in directing the pollen toward
S the basket. Sladen (1911) states that in this movement the weak
Swing of the auricle is forced backward, and thus allows the escape of
pollen toward the basket entrance, but this appears both doubtful and
unnecessary, since the angle of inclination of the auricular surface
gives the pollen a natural outlet in the proper direction.
If the corbicula already contains a considerable amount of pollen
the contributions which are added to it at each stroke of the auricle
come in contact with that already deposited and form a part of this
mass, which increases in amount by continued additions from below.
If, however, the corbicula is empty and the process of loading is just
beginning, the first small bits of pollen which enter the basket must
be retained upon the floor of the chamber until a sufficient amount
has accumulated to allow the long overcurving hairs to offer it effec-
tive support. The sticky consistency of the pollen renders it likely
Sto retain contact with the basket, and certain structures near the
entrance give additional support. Several small sharp spines, seven
or eight in number, spring from the floor of the basket immediately
S within the entrance, and the entire lower edge of the corbicula is
fringed with very small hairs which are branched at their ends.
(See fig. 3.) One large hair also springs from the floor of the basket,
somewhat back from the entrance, which may aid in holding the
Swollen, but it can not function in this manner until a considerable
amount has been collected.
As the pollen mass increases in size and hangs downward and back-
ward over the pecten and auricle it shows upon its inner and lower
surface a deep groove which runs outward from the entrance to the
Basket. (See fig. 9, b.) This groove results from the continued im-
1 pact of the outer end of the auricle upon the pollen mass. At each
; upward stroke of the auricle its outer point comes in contact with
the stored pollen as soon as the mass begins to bulge backward from
: Although the process is a rather delicate one, it is entirely pos-
.sible so to manipulate the hind legs of a recently killed bee that the
corbiculme of the two legs receive loads of pollen in a mn.
to that above described. To accomplish this successfully ::tf-he
must keep the combs of the plants well supplied with
pollen. If the foot of first one leg and then the other is
with forceps and so guided that the pollen combs of one legrp
the pecten spines of the other, the pollen from the combswu
transferred to the corbicule. To continue the loading p6r:m" kf
proper manner, it is a
essary to flex the p4
each leg just after the
iIP combs of the oppo '
o :"* the pecten. By this 3
S .. -:: the auricle is raised, lop
:. ....: pressing the pollen *bft
Sia- -'' the pecten has secured,; aiji^ !
i-^ :forcing some upward '.
i.> .;-' ^the corbicula. Beeso' A.
J....6-2 which have been load" 'Id
this artificial manner ,
hf'1'^^ pollen masses in their -&
,llW !biculse which are enti. e ..
f iB similar in appearae'k ` "60.
IM ^ ~those formed by the6 ui .,.
NI of the living bee.. :M ::::i
HI ~over, by the above meth.I
f^ of manipulation the pol'd.
~appears first at the bdOtU :
!j of the basket, along its h** 3
I/ margin, gradually exti b ,
upward along the floor i'
FIG. 9.-Inner surface of the right hind leg of a the chamber, comes in ;
worker bee which bears a. complete load of tact with the oereaf ,.;,:
pollen, a, Scratches in the pollen mass caused tc i t 3v
by the pressure of the long projecting hairs hairs, and is shaped by t'eu i
of the basket upon the pollen mass as it has a natural manner. ... ii
been pushed up from below; b, groove in the in .au.,mne .
pollen mass made by the strokes of the auricle attempts to load the :
as the mass projects outward and backward by other movements, ut V
from the basket. (Original.) bc other movements,9
crossing the hind lei"'......
scraping the plantar combs over the lateral edges of the
give results which are entirely different from those achieved by."
living bee. !
Many descriptions have been written by others of the, met
which pollen is gathered and moistened. Some of these. ar
nite. some are incorrect, while others are, in part, at least, ... .......
to my own interpretation of this process. A few citations will here
The bee first strokes the head and the proboscis with the brushes of the
forelegs and moistens these brushes with a little honey from the proboscis, so
that with later strokes all of the pollen from the head is collected upon these
brushes. Then the middle-leg brushes remove this honey-moistened pollen from
the forelegs and they also collect pollen from the breast and the sides of the
thorax.-[Translation from Alefeld, 1861.]
In his account of the basket-loading process Alefeld assigns to
the middle-leg brushes the function of assembling all of the pollen,
even that from the plantar combs, and of placing it on the corbiculte,
this latter act being accomplished by combing over the hairy edge of
each basket with the middle-leg brush of the same side.
It appears probable that the bee removes the pollen from the head, breast,
and abdomen by means of the hairy brushes which are located upon the medial
sides of the tarsal segments of all of the legs, being most pronounced upon the
hind legs. The pollen is thus brought together and is carried forward to the
mouth, where it is moistened with saliva and a little honey.-[Translation from
L Franz then says that this moistened pollen is passed backward and
Since the pollen of many plants is sticky and moist it adheres to the surface
of the basket. Dry pollen is moistened by saliva, so that it also sticks.-
[Translation from Fleischmann and Zander, 1910.]
Pollen is taken from flowers principally by means of the tongue, but at times,
also, by the mandibles, by the forelegs, and middle legs. The brushes of the
hind legs also load themselves, collecting from the hairs of the body. The pollen
dust thus gathered is always transmitted to the mouth, where it is mixed with
saliva.-[Translation from Hommell, 1906.]
Sladen considers the question of how pollen is moistened by the
honey bee, bumblebee (bumblebee), and some other bees, but does not
appear to reach definite conclusions. In one of his papers (1912, c)
he states that the pollen of some plants may be found in the mouth
S cavity and in the region of the mouth, but he reaches the conclusion
that this pollen is comparatively "dry," using the word in a "rela-
tive sense." He asserts that "nowhere but on the corbicula and
S hind metatarsal brushes did I find the sticky pollen, except some-
times on the tips of the long, branched hairs on the back (upper)
Sedges of the tibiae and femora of the middle legs, and then only
Sin heavily laden bees, where it is reasonable to suppose it had
collected accidentally as the result of contact with the hind metatarsal
H These and other considerations lead Sladen to think that, in the
case of the bumblebee at least, the pollen "may be moistened on the
hind metatarsus with the tongue." He states that the tongue of
the bumblebee is of sufficient length to reach the hind metatarsus
BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.
plantt) and that it might rub over the brushes of .the, I "
or be caught between them when they are approximated- .. 4t,
moisten the two brushes simultaneously. However, he has" 'IMq
seen the tongue of the collecting honey bee brought near to thh:...:W
legs, and it appears probable to him that it can not easily read: uiht..,
"Possibly the middle or front legs are used as agents for coenO
the honey" (in the case of the honey bee). "In the humbl2e1 4 |
tongue is longer, and it could more easily moisten the hind :
the way suggested."
In an earlier paper Sladen (1912, a) gives the following as
opinion of the "way in which pollen dust is moistened with aetaLi.
although he states that this is one of the points "which still renA it.l
The only satisfactory manner in which, it seems to me, this can be d 'bR 6:K!.
for the tongue to lick the tarsi or metatarsi of the forelegs, which are e6em. f
with stiff bristles, well suited for holding the nectar, the nectar being CS
transferred to the metatarsal brushes on the middle legs, and from these, ag$:
to the metatarsal brushes on the hind legs. The latter being thus re W i ,ii
sticky, the pollen dust would cling to them. The different pairs of legs w0, jBF
certainly brought together occasionally, but not after every scrape 1of-l tewo"
hind metatarsi, and their movements were so quick that it was imBpue 1I!5
to see what was done. Still, several pollen-collecting bees that I killed kliwth Hl
tarsi and metatarsi of the forelegs and the metatarsal brushes of the alle ie
and hind legs moistened with nectar, and I think it probable that the melate-
ing process, as outlined, is performed, as a rule, during the flight from flier .:
to flower. *(i. "
Sladen (1912, c) also considers the possibility that the fluid rdl* i1
moistens the pollen might be secreted through the comb at th 0 l4
of the tibia, through the tibio-tarsal joint, or from the surface of.; ::il
auricle, but finds no evidence of glandular openings in these rei M1i:6
A suggestion of a similar nature, apparently unknown to Slad
was made by Wolff (1873), who describes sweat-glands whMI ||
he claims, are located within the hind tibia and the plant, a"'i
which pour a secretion upon the surface of the corbicula and upqp,
the upper end of the plant through many minute openings 1oc9
at the bases of hairs, particularly those which arise from the ist 0l I
margins of the corbicula. Wolff is convinced that the fluid tiJJ
secreted is the essential cohesive material by which the grah"
pollen are bound together to form the solid mass which f$l ...|.
fully loaded basket. He noticed that the mouthparts are
collect pollen, and that some of it is moistened with "ho*
"nectar," but he does not consider that the fluid thus sup,
sufficient to explain adequately the facility with which the. co
bee brings together the scattered grains of pollen aw4 pip M ,
away securely in the baskets. Wolff's description of the frsketrp4.
ing process itself is strikingly similar to that advocated Ilatr
." *i i m
* The writer is not prepared to deny the possibility that the surface
of the chitin of the hind legs of worker bees may be moistened by
the secretion of glands which lie beneath it, but he is convinced that
any fluid thus secreted bears little or no relation to the cohesion of
the pollen grains within the baskets. Sections and dissected prepa-
rations of the hind legs of worker bees show certain large cells which
Slie within the cavity of the leg and which may function as secreting
gland cells; but similar structures occur in even greater numbers
within the hind legs of the drone and they are found within the hind
Slegs of the queen.
As has been noted, the extreme moisture of the plantar combs and
of the tibio-tarsal articulation of the hind leg is readily understood
when one recalls the manner in which moist pollen is compressed
between the auricle and the tibial surface above it.
From the account already given it is evident that, in the opinion
of the writer, the mouth is the source from which the pollen-moisten-
ing fluid is obtained. It is extremely difficult to determine with
absolute accuracy the essential steps involved in the process of adding
moisture to the pollen. In an endeavor to solve this problem the
observer must of necessity consider a number of factors, among which
may be noted (1) the location upon the body of the collecting bee
of "moist" and of comparatively "dry" pollen, (2) the movements
concerned in the pollen-gathering and pollen-transferring processes,
(3) the relative moisture of those parts which handle pollen, (4) the
chemical differences between the natural pollen of the flower and
that of the corbiculae and of the cells of the hive, and (5) the observer
must endeavor to distinguish between essential phenomena and those
which are merely incidental or accidental.
In the first place it should be noted that the relative dampness of
pollen within the corbiculae depends very largely upon the character
of the flower from which the pollen grains are gathered. When
little pollen is obtained it is much more thoroughly moistened, and
this is particularly true in cases when the pollen is all, or nearly all,
Collected in the region of the mouth, the forelegs, and head. When
* a bee takes pollen from white or sweet clover practically all of it
First touches the bee in these regions. It immediately becomes moist,
[, and in this condition is passed backward until it rests within the
|: baskets. There is here no question of "dry" and "wet" pollen,
or of collecting movements to secure dry pollen from other regions
of the body, or of the ultimate method by which such free, dry pol-
t len becomes moist.
The sticky fluid which causes pollen grains to cohere is found upon
all of the legs, in the region of their brushes, although the pollen
combs and auricles of the hind legs are likely to show it in greatest
itnb danee, since nearly all of the pollen within each basket has
BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING
passed over the auricle, has been pressed upward and .. .
tween the auricle and the end of the tibia and the poll. p ....
and by this compression has lost some of its fluid, which: rum..n ..A
over the auricle and onto the combs of the plant. It is not:..
to invoke any special method by which these areas reo 4iv.
moisture. The compressing action of the auricle squeezing :.l f
moistened pollen upward into the basket is entirely stai
account for the abundance of sticky fluid found in the neighbq*9ri|j-
of each hind tibio-tarsal joint. As has been noted, the brud i..
the forelegs acquire moisture directly by stroking over the prp 0boMppi
and by handling extremely moist pollen taken from the mout0 ptrt's.
The middle-leg brushes become moist by contact with the foreleg*":..:
hind-leg brushes, probably also by touching the mouthparts tha-'..i
selves, and by passing moist pollen backward. The hairy surfu:.o i: 4l
the breast is moistened by contact with the fore and mid leg 1bPiesU*ii
and with the moist pollen which they bear. ,1.
The problem of the method of pollen moistening is somewhat As.
complicated in the case of flowers which furnish an excessive supplpipi|
Under such conditions the entire ventral surface of the collecting i$q':
becomes liberally sprinkled with pollen grains which either wilA 1 iH|
removed and dropped or will be combed from the bristles and branr 4 i1
ing hairs, kneaded into masses, transferred, and loaded. The qua .I
tion naturally arises whether the movements here are the same su
when the plant yields but a small amount of pollen which is collect ,
by the mouthparts and anterior legs. In the opinion of the wuqit '!!
they are essentially the same, except for the addition of cleans pg i
movements, executed chiefly by the middle and hind legs for thecol,
election of pollen which has fallen upon the thorax, upon the abdomen 7
and upon the legs themselves. Indeed it is questionable as to jpst I ,d
how much of this plentiful supply of free pollen is really used i: !
forming the corbicular masses. Without doubt much of it falls froiK im
the bee and is lost, and in cases where it is extremely abundant ua4
the grains are very small in size an appreciable amount still remain ,Il
entangled among the body-hairs when the bee returns to the hie
Yet it is also evident that some of the dry pollen is mingled with jhfi"l#
moistened material which the mouthparts and forelegs acquire pSt i!
together with this is transferred to the baskets. , C|g,
In all cases the pollen-gathering process starts with moist pallidi
from the mouth region. This pollen is passed backward, and i : i.:l
passage it imparts additional moisture to those body regions w..E *..
it touches, the brushes of the fore and middle legs, the plant. a *W i
hind legs, and the hairs of the breast which are scraped ,over by .('t0S |
fore and middle leg brushes. This moist pollen, in its passage' bt ::il
ward, may also pick up and add to itself grains of dry pollen. vS"1(
which it accidentally comes in contact. Some of the .ew, .dry-r,..
p POLLEN MOISTENING. 27
Sw4hich falls upon the moist brushes or upon the wet hairs of the
Sthorax is also dampened. Some of the dry pollen which is cleaned
From the body by the action of all of the legs meets with the wet
Brushes or with the little masses of wet pollen and itself becomes wet
by contact. Pollen grains which reach the corbiculme either dry or
but slightly moistened are soon rendered moist by contact with those
already deposited. Little pollen gets by the sticky surfaces of the
Scombs of the planted or past the auricles without becoming thoroughly
Sladen (1912, c) very aptly compares the mixture of dry pollen
with wet to the kneading of wet dough with dry flour and suggests
that the addition of dry pollen may be of considerable advantage,
since otherwise the brushes, particularly those of the hind legs,
would become sticky, "just as the board and rolling pin get sticky
in working up a ball of dough if one does not add flour." The addi-
tion of a considerable amount of dry pollen gives exactly this result,
for the corbicuhle then rapidly become loaded with pollen mixed
with a minimum supply of moisture and the brushes remain much
-dryer than would otherwise be the case. However, if too much dry
pollen is added the resulting loads which the bees carry back to the
hives are likely to be irregular, for the projecting edges of tile masses
may crumble through lack of a sufficient amount -of the cohesive
material by which the grains are bound together.
On the other hand, it does not appear at all necessary to mix much
dry pollen with the wet, nor do the brushes become sufficiently
"sticky" from the presence of an abundance of the moistening fluid
to endanger their normal functional activity. I have observed bees
bringing in pollen masses which were fairly liquid with moisture,
and the pollen combs also were covered with fluid, yet the baskets
were fully and symmetrically loaded.
Sladen's different interpretations of the pollen-moistening process
are rather confusing, and it is difficult to distinguish between what'
he states as observed facts and what he puts forward as likely
Hypotheses. He agrees with me in his observation that all of the
legs become moist in the region of their brushes and also in his sup-
position that this moisture is transferred to them from the mouth.
SIn this moistening process my observations show that the fluid con-
cerned is passed backward by the contact, of the middle-leg brushes
with the wet foreleg brushes and that the middle-leg brushes in turn
I: convey moisture to the plante as they rub upon them. I am also
convinced that the wet pollen grains furnish additional jnoisture to
tj ite brushes as they pass backward, and this is particularly true in
S, the case of the extremely moist surfaces of the auricles and the pollen
IL combs of the. plant, since here moisture is pressed from the pollen
I ..pon these areas. The pollen upon the. fore and middle leg brushes
is not always "dry" even in "a relative sense."
28 BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING S
In describing pollen manipulation several writers a
pollen is picked up by the brushes of the legs and is carried i
to the mouth, there moistened (according to some, masticatd)1.. ,
is then carried backward by the middle legs for loading. Obh
such accounts do not apply to cases in which all of the pollen .is l
elected by mouthparts and forelegs. Do they apply in cases w'":
much pollen falls on the body and limbs? Without doubt a.:.etit
amount of this free pollen is brought forward when the middle : !!h
bearing some of it, sweep forward and downward over the o
mouthparts, and breast. However, it does not appear to the *writer
.- : :. : E- j :' i
that this dry pollen is carried to the mouth for the specific pu:rpo e"
moistening it, or that it is essential to its moistening that it
brought in contact with the mouth. Some of it touches the ) i:flk
hairs on the forelegs and breast and is moistened by contact. 'll.
that remains on the brushes of the middle legs secures moisture '6''" i.:!
these brushes or from wet pollen which the brushes collect froth:.
mouthparts or forelegs. The supposed necessity of carrying 'orw!'|w3i
pollen to the mouth for moistening is a delusion. Some is ci: -i..
dentally brought forward and into contact with the mouth and..a.
wet, but the process is not essential. I ,
If the pollen which bees transport to their hives has been moistened '.
with some fluid substance which causes the grains to cohere, this i
addition should be indicated by differences in the results of an aiis 'y
sis of pollen from a plant as compared with that found in the coar-.
bicule of a bee which has been working on this plant. For the sak I
of determining this difference and in an endeavor to ascertdiA, if,;i
possible, the.approximate nature of the added fluid, analyses *de ,
made of three kinds of pollen, as follows: (1) Pollen collected:b I
hand from the corn plant itself; (2) pollen taken from the corbidrd
of bees which had secured their supply from corn; (3) pollen sAtsI
in the cells of the hive. In the first two cases pollen from the atie
species of plant (corn) was used. The material from the cells of tb m
hive was composed largely of corn pollen, but contained an admituft i
of some other pollens.
The writer is indebted to Dr. P. B. Dunbar, of the Bureauf of
Chemistry, for the following analyses: ::l
-------------------------(, :.:r.-- :. ""
direct from C ,
_______________________________________________________---- ---- --*- rMH..'
Total solids............................... ....... .. ......... .... 53.47 66.& K *.|i
Totalsoi------------------------------------------------------- 8 476.4f
Moisture.-- ---- 46.53 3a.06of t 'Si
Reducing sugar before inversion---------------.................----............------...------. -. 2.87 11.07
Sucrose.. -.. ...... .................-- ...........-.-----. -------2.77 2. I
Total reducing sugar after inversion..................................... 5.79 14.29 .. .
Dry basis: h.!.
R educing sugar............. ...... ................. ............. E. 37 "
Sucrose.............................. ........... ---------- 4,567 :
0.55 2. .. :.
.STORING POLLEN IN THE HIVE. 29
S These analyses show conclusively that a very large amount of
I sugar has been added to the pollen by the time it reaches the cor-
| biculs. Calculated on a dry basis just about twice as much sugar is
Present in the basket pollen as in that from the corn plant. Not only
is this so, but the additional fact is disclosed that over three times as
Much reducing sugar is present in the corbicular pollen as sucrose.
k This latter result indicates that honey (largely a reducing sugar)
rather than nectar (containing more sucrose) is the chief sugar in-
gredient of the corbicular pollen. The additional amount of sugar
(here again a reducing sugar) in the stored pollen of the hive is
what might be expected, since it is supposed that the workers add
honey and possibly other ingredients to the pollen within the
The total solid percentages, corn 53.47, corbicula 66.94, stored
pollen 79.66, also show that the fluid substance which is added is one
highly charged with solids, a condition which honey amply fulfills.
In the descriptions which have been cited of the pollen-gathering
process in which the mouth is supposed to supply the requisite fluid
three substances are mentioned: Nectar, honey, and saliva. The
Analyses herein given indicate that reducing sugar is mingled with
the pollen, and in the case of corn it is indicated that honey is used
in greater abundance. Without doubt a certain amount of saliva
also finds its way to the pollen, but the proportion of this substance
has not been determined. This salivary fluid may have adhesive
qualities, but this is scarcely necessary, since honey alone is amply
Sufficient for this purpose.
It appears probable that the fluid which a bee adds to the pollen
which it is collecting varies somewhat in amount, since the pollen of
different plants differs considerably in moisture content and that of
Sthe same plant will differ in this respect at different times. Pollen
Collected in the early morning before the dew has left the plant is
much more moist than that found upon the same plant later in the
day, and the grains, if taken when moist, have a natural tendency to
become aggregated and form small masses. Moreover, this may ex-
Splain the fact that bees make their pollen-collecting trips during the
morning hours, rather than in the afternoon, although some may be
seen upon the flowers throughout the whole day.
STORING POLLEN IN THE HIVE.
When the bee has fully loaded its baskets and before it returns to
the hive it often spends a little time upon the plant from which it
has been collecting, occupied with the task of cleaning scattered
grains of pollen from its body and of patting down securely the loads
which it has obtained. Upon its return to the hive it hurries within
I and seeks for a suitable place in which to deposit the pollen. Some
BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.
returning bees walk leisurely over the combs and loiter; .I...L.....
sister workers, while others appear to be greatly agited".(
their bodies and moving their wings as though higy.
Many pollen-bearing bees appear eager to receive food :p*ti
return to the hive, and they will solicit it from other-.k0tu
take it from the honey-storage cells. The workers of:itl*i 4I|
times take a little of the fresh pollen from the baskets of 4*[ oltp
bee, nibbling it off with their mandibles or rasping off gpajsij i|iix
If the combs of a colony are examined, stored pollen will 4Wpj
in various parts of the hive. In the brood frames the greatet smpx 'tf||
is located above and at the sides of the brood and between t:iuejS ,:I!
the stored honey. Cells scattered through the brood frnmxaW4
young bees have lately emerged may also contain pollen. In le
outer frames of the hive, where brood is less likely to be: f
nearly all of the cells may be packed with pollen, or hon.y-strnpa
cells may be found interspersed with those filled with polled. j4 & f
rule pollen is not stored in drone comb, although this occW.o Ng.p
happens. K:. 10
As the pollen-bearing bee crawls over the combs it appeast t1l !
searching for a suitable cell in which to leave its load. I0, iq
the head into cell after cell until finally one is located which eM
its requirements, although it is an open question as to why any ,p i$'
a group should be chosen rather than another. This selected #W'
may already contain some pollen or it may be empty. If partlyfi14, :
the pollen which it contains is likely to be from the same spipcaIq
plant as that which the bee carries, although different kinds o4pof M.
are often stored in the same cell. 0 :,
In preparation for the act of unloading the bee grasps one mp
of the cell with its forelegs and arches its abdomen so that the pt ::
terior end of the abdomen rests upon the opposite side of the cell+,$Jjn A|
body is thus held firmly and is braced by these two supports, witL$Jz0
head and anterior thoracic region projecting over one of the .eigf
boring cells. The hind legs are thrust down into the cell and. A
freely within it, the pollen masses being held on a level wjth the ,M I
edge of the cell, or slightly above it. The middle leg of eacSt" .
is raised and its plant is brought into contact with thenpTg;
proximall) end of the tibia of the same side and with the pollen mum..i
The middle leg now presses downward upon the pollen mass, wor'k-.:l
ing in between it and the corbicular surface, so that the E:' is|,
shoved outward and downward and falls into the cell. As thpo p02'
masses drop, the middle legs are raised and their claws find:
upon the edge of the cell. The hind legs now execute cleansing MtJ!r
ments to remove small bits of pollen which still cling to the orbV.aJii
surafaces and hairs. After this is accomplished the bee usually leaves
the cell without paying further attention to the two pellets of pollen
although some collecting bees will stick the head into the cell, possi-
bly to assure themselves that the pollen is properly deposited. It has
been stated by some (Cheshire, for example) that the spur upon the
middle leg is used to help pry the pollen mass from the corbicula.
This structure is in close proximity with the mass while the middle
leg is pushing downward upon it, but its small size renders difficult
an exact estimate of its value in this connection. It is certainly true
that the entire plant of the middle leg is thrust beneath the upper
end of the pollen mass, but the spur may be used as an entering
Pollen masses which have been dropped by the collecting bee may
remain for some time within the cell without further treatment, but .
usually another worker attends to the packing of the pollen shortly
after it has been deposited. To accomplish this the worker enters the
cell head first, seizes the pollen pellets with its mandibles, breaks
them up somewhat or flattens them out, probably mingles additional
fluid with the pollen, and tamps down the mass securely in the bot-
tom of the cell. As is shown by the analyses of corbicular pollen and
of stored pollen, certain substances are added to the pollen after the
collecting bee leaves it in the cell. Sugar is certainly added, and it is
generally supposed that secretions from some of the salivary glands
are mixed with the pollen after deposition. It appears probable that
the stored pollen or beebread is changed somewhat in chemical
composition through the action of the fluids which have been added
to it, either during the process of collection, at the time of packing,
Pollen may be collected by the worker bee upon its mouthparts,
upon the brushes of its legs, and upon the hairy surface of its body.
When the bee collects from small flowers, or when the supply is not
abundant, the mouthparts are chiefly instrumental in obtaining the
The specialized leg brushes of the worker are used to assemble the
pollen, collecting it from the body parts to which it first adheres and
transporting it to the pollen baskets or corbiculhe of the hind legs. In
this manipulation the forelegs gather pollen from the mouthparts and
head; the middle legs, from the forelegs and from the thorax; the
hind legs, from the middle legs and from the abdomen.
The pollen baskets are not loaded by the crossing over of one hind
leg upon the other or to any great extent by the crossing of the middle
legs over the corbiculwe. The middle legs deposit their loads upon the
pollen combs of the hind plants, and the plant., in turn, tri ...
pollen of one leg to the pecten comb of the other, the: petie
leg scraping downward over the pollen comb of the oppos
(See fig. 7.) A little pollen is loaded directly from the middleN&
into the baskets when these legs are used to pat down the ii
masses. (See fig. 6.) -;*
Aside from the foregoing exception, all of the pollen which uIhW
the baskets enters them from below, since it is first secured b-4I
pecten combs, and is then pushed upward by the impact .1f-.4A i
rising auricles, which squeeze it against the distal ends of thE tiN
and force it on into the baskets to meet that which has gone bef t:.)t .
The long hairs which form the lateral boundaries of the ba strir
are not used to comb out pollen from the brushes of any of lthbegH.:.1
SThey serve to retain the accumulating masses within the baskets: l e
to support the weight of the pollen, as it projects far beyond. t..:isi
surfaces of the tibiam.
Pollen grains are moistened and rendered cohesive by the additidot
to them of fluid substances which come from the mouth. AnalywAtH|
show that honey forms a large part of this moistening fluid, althowt':i
nectar and secretions from the salivary glands are probably pres mi
In the process of pollen manipulation this fluid substance bemuk 1
well distributed over the brushes of all of the legs. The foreliegs'
acquire moisture by brushing over the mouthparts, and they transf:'i
this to the hairs of the breast and to the middle-leg brushes wbh : fi:
they come in contact with them. The middle-leg brushes transmit
their moisture to the pollen combs of the hind legs when they ru
upon them. All of these brushes also transport wet pollen which
has come from the mouthparts and thereby acquire additional mois-
ture. The auricles and the planted of the hind legs become particu- i
larly wet from this source, since fluid is squeezed from the wet .u. *.
when it is compressed between the auricles and the distal ends of t'i
tibie. Dry pollen which falls upon the body hairs becomes moibt
when brought into contact with the wet brushes or with wet pollen-0' :
During the process of manipulation pollen passes backward f4O i.
its point of contact with the bee toward its resting place with :*:in e::I!
baskets. ..: ::lI.. ::
Pollen which the collecting bee carries to the hive is depositbd"B'|bt
this bee within one of the cells of the comb. As a rule, this pollen ".
securely packed in the cell by some other worker, which flattens'M:;::::I
the rounded masses and adds more fluid to them. .::..:,::
I ^ n
BEHAVIOR OF HONEY BEE IN POLLEN COLLECTING.
ALTFELD, Dr.-Vol. 5, Nos. 15 and 16, Eichstiidt Bienen Zeitung. Summarized
in "Die Bienenzeitung in neuer, geschichteter und systematische geordneter
Ausgabe." Herausgegeben vom Schmid und Kleine: Erste Band,
Theoretischer Theile. 1861.
CASTEEL, D. B., 1912.-The manipulation of the wax scales of the honey bee,
Circular 161, Bureau of Entomology, U. S. Dept. Agriculture, pp. 15.
S CHESHIRE, F. R., 1886.-Bees and bee-keeping; scientific and practical. Vol. I,
scientific; II, practical. London.
FLEISCHMANN und ZANDER, 1910.-Beitriige zur Naturgeschichte der Honigbiene.
FRANz, A., 1906.-In "Unsere Bienen," herausgegeben von Ludwig, A., Berlin.
I pp. [viii]+831.
HOMMELL, R., 1906.-Apiculture, Encyclopedie Agricola, Paris.
PHiTLLPS, E. F., 1905.-Structure and development of the compound eye of the
bee. Proc. Acad. Nat. Sci. Philadelphia, vol. 57, pp. 123-157.
SLADEN, F. W. L., 1911.-How pollen is collected by the social bees, and the
part played in the process by the auricle. British Bee Journal, vol. 39,
pp. 491-493, Dec. 14.
SLADEN, F. W. L., 1912.-(a) How pollen is collected by the honey bee. Nature,
vol. 88, pp. 586, 587, Feb. 29.
1912.-(b) Further notes on how the corbicula is loaded with pollen.
British Bee Journal, vol. 40, pp. 144, 145, Apr. 11.
1912.-(c) Pollen collecting. British Bee Journal, vol. 40, pp. 164-166,
1912.-(d) How propolis is collected. Some further notes on pollen-
collecting. Gleanings in Bee Culture, vol. 40, pp. 335, 336, June 1.
1912.-(e) Hind legs of the worker honey bee. Canadian Bee Journal,
i vol. 20, p. 203. July.
WOLFF, 0. J. B., 1873.-Das Pollen-Einsammeln der Biene. Eichstadt Bienen-
S Zeitung. 29 Jahrg. Nrs. 22 u. 23, pp. 258-270.
* *r '
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..... "i:: *J:'- ++ ': M
':" :: ..' ":. ": : IiH
\ t + . '
ALIrEWD on pollen moistening by worker bee ---------------- ---- 23
Ahtenna cleaner of worker bee, figure-------------------------------- 8
Auricle of hind plant of worker bee, definition ------------------ 9
figure -------------------------- 11
rOle and action in pollen collect-
ing--------------- 16-17, 19, 20-'22
Basket, pollen. (See Corbicula.)
Brush of foreleg of worker bee, action and rOle in pollen collecting ------ 13
figure ----------------------- S
hind leg of worker bee, action and role in pollen collecting----- 16
middle leg of worker bee, action and role in pollen collecting... 14-16
Brushes of legs of worker bee, use in pollen collecting------------ ----8-9
Bumblebee, moistening of pollen, views of Sladen---------- ------- 23-24
CHESHIRE on process of loading pollen baskets by worker bee----------- 17
Comb or pecten of hind tibia of worker bee, definition------------------ 9
r61e and action in pollen col-
Corbicula of worker bee, definition------------- -------------------- 9
figure ------------------ -----------------10
process of loading ----- -----------------15-22
Corn, sweet, pollen collecting therefrom by honey bee ---------------- 1.1-13
Coxae of worker bee, figures------------- ------------------------ 8,9
DUNBAr, Dr. P. B., analyses of corn pollen from plant, from corbiculae
of bees, and from hive cells------------------------------------- 28
Femora of worker bee, figures--------- ---------------------- 8,9,10,11
FLEISCHMANN and ZANDER on process of loading pollen baskets by worker
bee------------------.------------------ ----------- 18
.Flowers, variable amounts of pollen from different plants------------- 10-11
FRANZ on pollen moistening of worker bee---------------------------- 23
process of loading pollen baskets by worker bee -------------- 17
Hairs, branched, of honey bee, use in pollen collecting-- ---------------- 7-8
fringing pollen basket, function-------------------------------- 20
unbranched, of honey bee, use in pollen collecting---------------- 7, 8
HOMMELL on pollen moistening of worker bee------------------------- 23
process of loading pollen baskets by worker bee------ S------
Honey, use by worker bee for moistening pollen------------------ 24,28-29
Leg, hind, of worker bee, loaded with pollen, figure-------------------- 22
Legs, fore, of worker bee, action and r6le in pollen collecting---------- 12,13
hind, of worker bee, action and role in pollen collecting------ 13,16-18
stages in basket-loading process, figure------ 19
middle, of worker bee, action and r6le in pollen collecting--- 13, 14-16
of worker bee, action in unloading pollen---------- ----------- 30-31
structures used in pollen collecting --------------- 7-9
Mandibles of honey bee, action and rOle in pollen collecting -_..._
worker bee, use in packing pollen in the cell--------
Maxillae of honey bee, action and rOle in pollen collecting-------
Moistening of pollen by bumblebee, views of Sladen .-------------
.honey bee--------------------------- -
Mouthparts of honey bee, action and r6le in pollen collecting-------_.,.
Nectar, supposed use by worker bee for moistening pollen-- ------
Palma of foreleg of worker bee, definition------------- -------.--
Pecten of hind tibia of worker bee, definition .------ -_- ----i-. 1
figure ------------ ---" ...
r6le and action in pollen collectbe*2
Planta of hind leg of worker bee, definition ----------------------- i
structures concerned in pollen !olleet-.
ing --------------------------- :1
. 1n%7 U.
middle leg of worker bee, definition----------....-----..-- -1---
Pollen, chemical composition .-. .--------------------- :":
collecting by worker bee, bibliography- -.... i-------
general statement regarding it----:.
summary of process-----------------
corn, from plant, from corbiculse of bees, and from hive c...1** ...,,
analyses to determine nature of moistening fluid .. ----
moistening by bumblebee, views of Sladen----------------
honey bee------------------ --------- t
storage in the hive------------------------------------
structures of honey bee concerned in manipulation------- ---
supply of honey bee------------------------------------ 4
unloading process by worker bee-------------------------- :-i ,"
Saliva, supposed use by worker bee in moistening pollen ------------- 2.
SLADEN, observations on process of loading pollen baskets- by worker
views as to pollen moistening by worker bee-------- -----2--
Spur of middle tibia of worker bee, figure-------------------------
Storing pollen in the hive -------------------
Structures of honey bee concerned in manipulation of pollen------ --
"Sweat glands" of Wolff within hind tibia and plant of worker bee, 'A .
Tibia of hind leg of worker bee, modifications and structures for pollen t:J'i
Tibite of worker bee, figures-------------------------------- 8,9, 10,
Tongue of worker bee, action and r6le in pollen collecting------------ :
Trochanters of worker bee, figures-------------------------- ------ I
Wax shears or pinchers, so-called, use in loading pollen by worker bee-_ .:i
WOLFF on pollen moistening by worker bee---.---------------------Jri.i.
ZANDER, FLEISCHMANN and. (See Fleischmann and Zander.) ji
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