Control of dog fly breeding in beach deposits of marine grasses


Material Information

Control of dog fly breeding in beach deposits of marine grasses
Physical Description:
Simmons, Samuel William, 1907-
Dove, Walter E., b. 1894
United States -- Bureau of Entomology and Plant Quarantine
U.S. Department of Agriculture, Bureau of Entomology and Plant Quarantine ( Washington, D.C )
Publication Date:

Record Information

Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 030284965
oclc - 78840030
System ID:

Full Text
E-541 .June 1941


By S. W. Simmons and W. E. Dove,
Division of Insects Affecting Man and Animals

The dog fly occurs in all temperate regions of the world as a pest
of warm-blooded animals and is a severe biter of man. Most often it is
considered to be a parasite of livestock and is commonly known as the stable
fly (3tomx calcitrans (L.)), 1 but in some localities its occurence in
unusually large numbers as a pest of dogs has resulted in the name "dog
fly." When it occurs in small numbers among domestic animals it attracts
little attention, but amoiL, persons on sea beaches even a few flies may
become most annoying. Under favorable conditions large numbers of flies
develop, and their bites become serious for man and domestic animals.

Outbreaks of this fly may result in a considerable loss of blood
among cattle, with a reduction in their weight and vitality as well as
in the supply of milk. When the animals fight the attacking flies they are
likely to receive mechanical injuries, and when they make efforts to escape
the flies by standing in water for long periods they may experience swollen
feet and joints. If they stand in water of the swamps they often become
mired and thus perish.

In a coastal area of northwestern Florida the dog fly often occurs
in outbreak numbers during the best season for tourists to visit the beaches,
and at such times it is capable of seriously affecting resorting interests
and incidentally the values of real estate,

In order to avoid outbreaks of this pest it is necessary to under-
stand (1) how dog flies develop along the seacoast of northwestern Florida
and elsewhere, (2) how natural control affects breeding in marine grass
deposits, (3) how to determine the time and place for treatment, and (4) how
to treat breeding places.

1Bishopp, F. C. The Stable Fly. U. S. Dept. Agr. Farmers' Bulletin
No. 1097. (Revised October 1939.)


How the Dog Fly Develops

As with other kinIs of flies, there are four stages in the life cycle
of this pest--the egg, the larva, the pupa, and the adult fly. The eggs
are about one twenty-fifth of an inch in length, elongate, and of a creamy-
white color They are laid on moist portions of fermenting marine grasses
on bay beaches, in cured hay exposed to the weather, and to a considerable
extent in mixtures of peanut hay and manure about animal feed lots. When
wet by fall rains, peanut litter left in fields after threshing also proved
to be an important source of dog flies throughout several counties of
northwestern Florida, southern Alabama, and southwestern Georgia. 2 Within
1 to 3 days the eggs hatch and the newly emerging larvae feed upon this
fermenting material. Under the most favorable conditions they may become
fully developed within bout 7 days, but if the food is unfavorable or the
air temperatures are low, they may require 30 days or longer. When full-
grown the larvae are about four-fifths of an inch in length. In fermenting
media they move rapidly and can conceal themselves quickly.

Wh i fully developed the larvae become shorter and thicker, and
thc outer surface hardens and gradually assumes a dark-brown color. This
stage is known as the pupa, or resting stage, and it may last from 5 to 20
days or longer before the fly appears, When the fly emerges from the pupal
case it inflates the head so as to force its way to the surface of the
material in which it pupated. Upon reaching the surface the wings become
dry and the fly soon goes for its first flight. The complete development
from deposition of the egg to emergence of the fly may take place in a period
as short as 14 days, but usually it ranges from 20 to 25 days, with an
average of 20.4 days at Panama City, Fla. A developmental period of 76 days
has been observed during lower temperatures, and even longer ones undoubtedly
occur during the winter months. Both males and females are capable of taking
blood of animals and may be observed resting on the walls of a building or
on fences while digesting the blood meal. During warm weather flies may
feed a second time during the same day. If adult flies do not obtain blood,
food, or water they usually die within 2 or 3 days. In laboratory cages
they have been kept alive for 47 days On an average the female flies begin
to lay fertile eggs when they are 11 days old,

Where Dog Flies Breed on the Seacoast of Northwestern Florida

Along the seacoast of' northwestern Florida there are no feed lots
which would account for outbreak numbers of dog flies. Cattle, sheep, and
hogs are permitted to graze on the range throughout the year. and during

z Dove W E. and Simmons, S W., Control of Dog Fly Breeding in
P ,anut Litter U. S. Dept. Agr., Bur. Ent. and Plant Quar., E-542 (multi-
graphed) June 1941


the winter they enter swamps for food and protection. In excetional
cases hogs or cattle are given some supplemental ed about farms and
dairies, but when such cases are found it is usually no d ffcult to find
some dog fly larvae developing in fermenting hay mixed FTth ranure However,
the numbers of larvae and pupae found in such places are most cernly not
sufficient to account for any outbreak or unusually great annoyance by these

During the principal season for dog flies in the o1lvnr of 1940 five
trained entomologists scouted intensively along the coa'ists for breeding
places of the pest. When they encountered abnormally large numbers of flies
they attempted to correlate the abundance with that ef sone nearby brooding
places. Since this was seldom possible, detailed examinations were made to
determine if breeding occurred in any depressions that received seepages of
salt water. It was thought that fermentation of fresh-water 7egetation in
such places might afford favorable breeding places for the flies, About the
edges of land-locked pools which contained water with a small percentage of
salt, examinations of samples of decayed vegetation were repeatedly made,
and soil obtained from such places was sifted and carefully examined These
procedures at different locations along the coast did not reveal the presence
of a single dog fly larva or pupa.

At the same time that examinations were made for breeding places,
inquiries were made among fishermen and others regarding abundance of flies
at different places. These men repeatedly stated that dog flies were
troublesome to men in boats as far as 12 or more miles from shore, and in
some instances they indicated that the flights were several times this
distance. All of them agreed that the flies invariably appeared soon after
breezes began blowing from the land. From these reports and from observa-
tions it appeared that light winds and breezes brought the flies from
inland breeding places, and as a result of this influx of flie it could be
expected that any extensive coastal breeding place would produce a large
number of flies that would drift with the winds and bite man and domestic
animals at different locations along the coast.

During the latter part of August the appearance of large numbers of
unfed flies along the beaches of inner bays and sounds followed very closely
the occurrence of windrows of two species of bay grasses on nearby beaches.
These grasses are known as Halodule w.fti, or shoal grass, a narrow-
leafed grass slightly thicker than pine needles, and Thalassia testudinum,
or turtle grass, the leaves of which are about the width of carpet grass.
They were not found on any of the beaches of the Gulf but were iound growing
on the bottom of shallow bays and sounds, where individual blades were washed
to nearby shores by tidal action. Because the blades of the grass were
fragile, they broke off easily with the tides and were found deposited in
huge windrows on the beaches. When high tides were accompanied by wind,
the windrows were formed high above the normal tide lines. In the absence


of hgi or .or3 ti thes te grasses were deposited along the water's edge of
Sdaly high de For long distances along certain shores of East Bay
ad Sant Rosa Sound, just above the normal watermarks of the daily high
tides, ad ox both o' the beaches systematic examinations revealed extensive
infestations of dog fly larvae and pupae.

FaiI-gro. n larvae and pupae were found in deposits of grass 1 to
3 ,'ve~ks old and beginning to turn brown, the greater numbers of pupae being
present at the higher levations which were not being submerged by any of
the tides _i the old or brown portions eggs and newly hatched larvae
could not bc iound, bu. they were readily observed in large numbers in green
grasses recently dcpos itd by the tides. Thousands of the eggs contained in
some samples of' these green grasses were removed from the tidal deposits
and brought o the laboratory, Most of them hatched during the night, and
the young larvae demostrated that they were capable of maintaining them-
selves on smal quantities of the grasses without the addition of any
moisture hen representative lots of these young larvae w'ere reared to
maturity t adults proved to be dog flies. Following these experiences
it was possible to select favorable breeding locations in diflerent deposits
of grasses and to find dog fly larvae and pupae with ease

From observations made on the beaches, and on caged lots of infested
grasses coilcted from numerous locations along the beaches, it was evident
.hat the erm.1Lting deposits of marine grasses were extremely favorable for
the deveopment of' dog flies, To prove this beyond any doubt, more than 45
lots of r sh, uninfested grass were collected from the bottom of shallow
bays and exposedd in nature. Each lot, consisting of about 2 bushels of
grass, wan placed near animals in a pasture, where it became infested.
After cxposure soue lots were placed in individual cages, and any immature
stages oi 'iseCts contained in them were allowed to develop. These experi-
ments duemnt'ated that the green bay grass readily supported and quickly
developed a de use population of dog fly larvae. From the experiments with
TTalassia testudinum there was an average emergence of 82.4 flies per cubic
foot or grass, and from Halodule wrijhtii an average of 38.7 flies per cubic

One 9-cuic-foot pile of turtle grass kept moist ,ith fresh water
was of unusual interest. It was rinsed slowly with 25 gallons of fresh
water, after which, on September 6, it was exposed for deposition of eggs.
Three day I 1ater 4 material was wet down with 5 gallons of fresh water
from a apr nkh r can. Four days after the second application a third appli-
cation ai'lF o 3 gallons ol fresh water. The repeated additions of
fresh watei s mulate'd the occurrence of rain, and it is significant that
dumb'rs oi n I- fe larvae were present in this grass 6 days after eggs
we'e laid om,"hc nnterial. Full-grown larvae were found 7 days ater egg
depos~itio .. IJm iull% developed flies emerged 6 days later, giving a
minimum Ve~d o 16 _ays for development from egg to adult. This is a


shorter period than that reported for development of dog flies in any other
breeding medium and is identical with a minimum period obtained in turtle
grass kept in the laboratory. The flies continued to (merge fro this lot
of grass until November 1, or for 38 days, and a total of 742 adult were

A limited amount of fly breeding was encountered amon other kinds
of fermenting vegetation on the beaches. Normal breeding -a found in
Vallisneria americana, a broad-leaved -rass growing ii bays with openings
into the Mississippi Sound, and 162 normal-sized flies were rared per cubic
foot of this grass which had been exposed to dog flies in nature. From an
alga, Enteromo_ha plumosa, which dried into thin sheets on a bnach of
Santa Rosa Sound, Fla., normal dog flies were reared. Since this alga ap-
pears only in small quantities and is limited to certain of the beaches, it
could not be an important producer of flies in this area. Tn 1936 King3
found that during an outbreak of dog flies an alga known as Sar :n became
infested on the gulf beaches. This species was not present in quantities
in this area in 1940, and therefore it was of minor importance as a producer
of flies that year Undoubtedly other kinds of marine vegetation are capable
of producing flies if washed ashore and allowed to ferment at the time adult
flies are present to deposit eggs.

Since enormous quantities of turtle grass and shoal grass were found
infested with all stages of the dog fly on the bay and sound beaches during
1940, since no such extensive infestations were found in any other material
on the coast, and since about 45 lots of the 2 kinds of grasses removed
from the beaches developed large numbers of normal flies, some with a minimum
period for development, it can be concluded that these 2 species of marine
grasses represented the principal breeding media on the beaches of the north-
west coast of Florida under conditions prevailing in 1940.

How Natural Control Affects Breeding in Marine Grass Deposits

By the first week of September grass deposits extending for many
miles along Santa Rosa Sound and East Bay and on portions of other bays
were infested with dog fly larvae and pupae. These immature stages could
be found with ease, especially in locations where 'rains had fallen upon the
grass soon after it was deposited on the shores, About the time dog flies
began to emerge in noticeable numbers from these places the equinoctial
tides became high enough to inundate most of the infested portions of the
grass deposits. By the middle of September most of the infestations were
eliminated through submergence by tides, leaving only a few at unusually

3 King, W. V. and Lenert, Louva G, Outbreaks of Stomoxys calcitrans
L. (Dog Flies) along Florida's Northwest Coast The Florida Entomologist
19: 33-39. 1936.

high elevations on the beaches. The higher equinoctial tides which followed
destroyed even these infestations.

Tests made to determine how long last-stage larvae could withstand
suhn~ren~ce showed that about 50 percent of the larvae failed to recover
when inundated for G hours, and that none recovered from 15 hours of such

Observations in the field demonstrated clearly that the equinoctial
ticles controlled the infestations in all grasses that were submerged, Also,
they suggest that such a natural control may result from equinoctial tides
each year if the windrows of grass are within reach of these tides. On
the other hand, if the windrows are deposited by storm tides, normal equinoc-
tial tides would not be expected to submerge all the deposits, and in con-
sequence the production of flies in outbreak proportions would be expected.

According to available reports a serious dog fly problem does not
exist along the coasts of Mississippi and Alabama and about the littoral of
the southern half of Florida. Examinations revealed that marine grasses
grow in shallow water in the bays and sounds along these coasts, and that
The broken blades of marine grass were prevented from washing ashore by the
prseneco bulkheads, or a sea wall near the water's edge, but more often
-y th presence of dense growths of tall reeds, Juncus roemerianus and
others In southern Florida root growth of the red mangrove trees extended
nto the water and served as a barrier against grass deposits on the beaches.
WherC the marie grasses were not washed ashore there was simply no oppor-
tunity lor the breeding of the flies In a few unprotected situations
.ong the coasts of Alabama and Mississippi places were occasionally found
whch did -ot have such barriers along the beaches. In such places small
quantiti of marine grass occurred on the beaches and were heavily infested
with dog fly larvae and pupae

How to Determine the Time and Place for Treatment

3eca ~ submergence of windrows of infested grass by high tides
es oy th mrr re stages of the dog fly, and because barriers of tall
8 zo:wing at the edge of the water prevent broken blades of marine
grse r 1 washi:ng ashore, thereby preventing dog fly infestations, it is
de.r'0 to take advantage of these factors of natural control and to
e y %he breeding places that are not affected by them. In antici-
pa ig exact locations to be treated, the time treatment should be
app] to prevent economically the development of larvae and pupae,
.,:-eiht o equinoctial and other high tides which may afford natural
. ro. oj wnciate the need for immediate treatment, it is soon discovered
V ot iortanlt factor is rare judgment. The man responsible for
2s1uch.u i~ h iLd] he one who can evaluate natural-control factors and quickly
htp tme, llace, and quantities of materials needed to supplement


natural control, and who can supervise the timely application of treatments
for different places likely to produce flies on the extensive beaches, In
such an undertaking the following factors tend to delimit the areas ileeding
treatment and to add encouragement to the undertaking;

(1) Control of breeding during July, August, and September would
take care of dog fly annoyance during the most important season for beach

(2) The principal breeding of dog flies is confined to the shores of
inner bays and sounds where two known species of marine grasses are deposited
by tides.

(3) Only portions of these shores receive grass deposits. These
depend upon the extent of growth of grasses in nearby bays,

(4) Of the shore-line deposits. only those that are not submerged
by subsequent tides need be considered as potential breeders of flies.

(5) If the first windrows of grasses are deposited at low eleva-
tions, they serve as a barrier which tends to keep fresh deposits of green
grasses at the water's edge, where the latter will be submerged by later
tides, thus making artificial treatment unnecessary.

(6) Each man in charge of control work in an area should (a) keep
in mind the fact that dog flies can develop within 2 weeks from the time
eggs are laid, (b) anticipate needs for treatment of the principal breeding
places in advance of the season and have about 25 percent of the materials
for treatment delivered to readily accessible places along the beaches,
(c) be able to determine quickly the elevations of grass deposits from a
small boat, (d) be familiar with variations in the height of high daily
tides, (e) have tide elevations marked on visible boards on different beaches
where breeding occurs, to guide him in determining the need for treatment,
(f) be able quickly to inspect grass for infestations, and (g) set up, for
heavily infested windrows of grass which will need treatment, suitable mark-
ers which would readily be recognized by the treating crew. these to be
removed by the crew as soon as treatments have been made,

How to Treat Breeding Places

On accouiit of the short period of 14 days required for development
from the egg to the adult dog fly, and the occurrence of widely scattered
breeding spots on bay and sound beechcs which need to be located and treated
within this short period, it is advisable to employ a treatment that will
immediately destroy infestations in the grass and will control breeding of
dog flies in the treated portions of grasses throughout the season. In
tests of sprays made during 1940 the most promising materials were those

tllll lIJllllllll i i ll HI I111111l
3 1262 09230 3915

that killed by contact, did not dissolve in water, and did not evaporate
quickly .In. limited number of tests with various materials creosote oil
was used in 19 instances It furnished the most promising results, which
varied with the degree of penetration of the infested grasses rather than
with the different dilutions made with fuel oil. By diluting creosote oil
with 3 parts of fuel oil, good results were obtained and the costs were
reduced In order to obtain penetration of the infested piles of grass,
speed in application, and economy of treatment, high-pressure sprayers are
desirable Because of the quantities of materials that may be needed for
treating Long windrows of infested grasses and the difficulty in handling
such quantities from boats in shallow water, it is desirable to test on an
extensive scale large power sprayers mounted on trucks and to use about one-
half mile of hose.

It is anticipated that it will not be possible to treat all the
infestations with a truck sprayer, owing to the inaccessibility of many
breeding places. and that it will be necessary to use a boat for treatments
on island beaches and similar places

Aftei attempts have been made to treat all infested grasses that are
not controlled by tidal waters, it is further anticipated that some loca-
tions will be found which will contain abnormally large numbers of pupae
and that dog flies may emerge from them in a very short time. For such
places it is believed that a smaller sprayer mounted on a boat could readily
apply a surface application of fuel oil containing 10 percent of concentrated
pyrethrum extract. Such treatments kill the newly emerged flies as they
force themselves upward to the surface of the infested material.