Insects in relation to national defense


Material Information

Insects in relation to national defense
Series Title:
Its Circular no. 1-23. Feb. 1941-Jan. 1944
Added title page title:
Insects in relation to national defense, circular
Physical Description:
24 nos. in 1 v. : ill., photos., map, plans, diagrs. ; 23 cm.
United States -- Bureau of Entomology and Plant Quarantine
U.S. Govt. Print. Off.
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Publication Date:


Subjects / Keywords:
Beneficial insects   ( lcsh )
Insect pests   ( lcsh )
Insecticides   ( lcsh )
Fumigation   ( lcsh )
World War, 1939-1945 -- Health aspects   ( lcsh )
serial   ( sobekcm )
non-fiction   ( marcgt )


General Note:
Reproduced from type-written copy.
General Note:
Includes bibliographical references.

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 029081698
oclc - 09471812
lcc - SB931 .U44
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Full Text


TO 0

Circular 16



June 1941




Circular 16 Horse Bots

Table of Contents

Introduction............................. 1
Kinds and How to Distinguish Them........ 2
Distribution............................. 6
How Injury is Produced.................. 6
Life History and Seasonal Activity....... 7
Control .............. ................. ... 9
Protective Devices..................... 9
Destruction of Bot Fly Eggs............ 10
Treatment of Horses and M ules for
the Destruction of Bots.............. 10
References ....................... ..... .. 13


Horse bots have much to do with the effi-
ciency of horses and mules. Injury from the
effects of the bots in the digestive tract is
seldom evident in very light infestations. On
the other hand sore mouths, emaciation, colic,
and even death from stoppage of the digestive
tract may result from heavy infestations. More
feed is required to keep an infested work ani-
mal in condition. The bot flies when laying
eggs seriously annoy horses and mules, whether
grazing, on picket lines, or in harness. Animals

Circular 16 Horse Bots

may be kept from grazing the greater part of
the daylight hours and those in harness are
difficult to handle and may become unmanage-
able, especially if nose flies are present in


There are three species of horse bots
commonly found in the. United States. Their
appearance and habits differ considerably.

The common horse bot fly,
intestinalis De Geer, Fig. 1, is

Figure 1 The common horse bot

the largest
of the three
species, about
7/8 of an inch
long and nearly
black, and it
is well covered
with bands of
black and yel-
lowish hair.
It is readily
separated from
the other species
by the cloudy
spots on the

The nose fly, G. haemorrhoidalis L., Fig.
2, is the smallest of-these species. The wings
are clear. It is nearly black in color, with
some yellow hair on the thorax and at the base
of the abdomen and orange-colored hair at the
tip of the abdomen. The throat bot fly, G.
nasalis (L.), has clear wings also, but the color
isTlighter and it doesn't have the orange hair
at the tip of the abdomen.

Circular 16 Horse Bot3

The three species have distinctive egg-
laying habits. The coimuaon bot fly hovers lei-
surely around the legs of a horse, laying egg
after egg. The flight of the nose fly is very
fast. It usually poises a :io..ient in front of
the forelegs, then darts at the lips and quickly
flies away to repeat the action in a few seconds.
The throat bot has a someewhat similar but slower
flight and it is maore inclined to stay close to
the host and repeat its darting flight to attach
egg after egg beneath the jaws.

Figure 2 The nose bot fly.

The eggs of
the three species
are readily distin-
guished as shown
in Fig. 3. The
egg of the common
bot fly is yellow-
ish and is attached
for about 1/3 its
length to the hair,
and often from 2
to 10 eggs are found
attached to a single
hair. The eggs are
found chiefly on
the forelegs, shoul-
ders, neck, and
flanks. The throat
bot fly egg is also
yellowish; it is
attached, however,
to the hair by more
than half its length.
It is usually at-
tached close to the
skin under the jaw.

Circular 16 Horse Btz

The nose fly e.-c is nearly bl-ck
has a long roughened basal cl.-p
is attached close to the ::'.in Dr.
of the lips.

in color ."'1
..ith ..hlch it
the short hjir

Figure 3 Eggs of horse bot flies.
A. throat bot fly; B. common horse bot
fly; C. nose bot fly.

Tne larvae, or bots, of th.e three species
are rather easily distinguished in either the
first or last staGes, Figs. 4 and 5. The cocmon
horse bot, when full-grown, is about 7/8 of an
inch long. It is yellowish with a distinct pink
cast and is usually found in the left sac of the
stomach. The nose bot is slightly smaller and
is found in the right as well as the left sac
of the stomach and to some extent in the duodenum.


Circular 16 Horse Fots

Before leavin,- the host it attachiles in the
rectu-i :r.d is often jeen protruding, fro': the
anus. It is pin.ish in color, beco-unin,- green-
ish before rassin:- out of the host.


fly; C. nose bofly* .

i f



Figure 4 Horse bot larvae (first stage).
A. throat bot fly; B. common horse bot
fly; C. nose bot fly.

The throat bots are whiter than the other
two species and are found mainly in the duodenum.
Those of small size are also found occasionally
attached in the pharynx.

Circular 16 Horse Bots


The common horse bot and the throat bot
are widely distributed in the United States.
The latter species is especially abundant in
the Rocky Mountain region. The nose bot is
present only in the region from the Cascade
range in '/ashington eastward to Lake Michigan,
and southward from the southern provinces of
Canada to northern Utah, Colorado, and Kansas.

Figure 5 Horse bot larvae (last stage).
A. throat bot fly; B. common horse bot
fly; C. nose bot fly.


Severe annoyance is caused by the bot
flies at the time they are laying eggs. This
is particularly true of the nose fly. The

Circular 16 Horse Bots

livestock often keep grouped and fight the flies
vigorously much of the day rather than graze.
The attack of the nose fly often so excites
horses in harness as to cause them to run away,
resulting in injury to the animals.and destruc-
tion of property.

The newly hatched larvae of all three
species burrow about in the mucous membranes
of the mouth for about 30 days causing soreness
which may interfere with eating. The presence
of throat bots in the pharynx has been known to
cause such severe swelling as to prevent swallow-
ing and occasionally produce strangulation. The
attachment of bots in the stomach and duodenum
causes severe lesions on the lining of those
organs. Heavy infestations have been known to
cause stoppage at the exit pyloricc) end of the
stomach. Colic is frequently associated with
bot infestation and the general condition of
heavily infested animals is lowered. Consider-
able irritation of the tissues is also produced
by the attachment of nose bots in the rectum.


The three species of bots have somewhat
similar life cycles but they differ in certain

The flies usually make their appearance
about the middle of June in the Central States,
earlier in the South, and later in the North.
They are more or less active throughout the sum-
mer and nearly always become most numerous in
the fall before heavy freezes stop their activity.
The adults do not feed; in fact, their mouth
parts do not function. Their life span is short--

Circular 16 hors- Bot s

usually bein. only 2 to 6 %ays--ad they .'.
ready to lay :' s-. soon after t-ry eer. -.-

s previous states, the c-s of eac:.
species are laid c,,. f..irly district reK..s of
the host. ie e,-s of the corw.-on horse b.jt
fly are ready to hatch in about 7 :.- b-.-t
the larvae do not emer-e until the e--s are
war. ied by t'.e hor-e's lips. They nmay r...-.
in the e,-,:s, awaiting! th'.e hatching sti.- us
for as lon- as 3 ilonth3. The larvae, u,:.n
bein- ta-}:en into the mouth, penetrate the
mucosa of the ton-ue and lips and b rrovw a,'c:ut
in them for about 30 days, then pass into the
stomach and attach there.

The throat bots hatch in about 5 da-.,
and crawl al'n- the jaw to the :douth. They
are found :aainly in the pockets between the
molar teeth. So:ie attach in the o:rynx on
the way to the sto:iach.

The egs of the nose fly hatch in 2 to
4 days and the larvae penetrate the skin of t.he
lips at once and barrow in this tissue until
the mucous lining of the lips is reached. -re
they burrow about for more than a -onth before
passing on into the stn.macho

The period of attachment of the larvae
of all three species in the stomach and intestines
varies from 8 to 11 months. .,hen full-,-rown the
bots release their hold and pass out with the
excre:rent, except in the case of the nose bot.
This species reattaches in the rectum-' for a 1-
to 3-day period before droppin.z to the -r:'und,

.'/hen the bots reach the ground they see-:
protection under debris or by burrowing slightly

Circular 16 Horse Bots

into the soil, and soon pupate.

The pupal stage, Fig. 6, lasts from 20
to 70 days; this period being about the same
for each of the three species.

Figure 6 Pupa,
or resting
stage, of a
bot fly.


Horse bots attack only
horses, mules, and asses and
they are all found in the diges-
tive tract for the major part
of each year. As the bot flies
do not feed, no effective method
of baiting or trapping them has
been found. Partial and tempo-
rary relief iiay be given by
catching the flies with a net as
they oviposit, or by knocking
them down and destroying them.
Such efforts, and also steps to
destroy the eggs during the
active bot fly season are im-

Protective Devices

In areas where nose flies are abundant
it is necessary to protect the lips of horses
in harness or saddle. A piece of leather or
belting 4 to 6 inches wide and long enough to
cover the entire lips, suspended beneath the
mouth from the bit rings, will protect the ani-
mal from attack and allay its excitement. A
piece of canvas or burlap suspended beneath the
jaws from the throat latch to the bit rings gives
a high degree of protection from the throat bot

Circular 16 Horse Bots

Destruction of Bot Fly Eggs

Efforts to control bots or prevent infes-
tation of animals by treating the bot eggs are
impractical. Some reduction in the number of
bots infesting an animal may be brought about
by clipping the hair that is infested with eggs.
The application of materials s such as kerosene
and creosote dips has little effect on the eggs.
HIowvever, the application of warm water (105 to
110 F.) to the eCEggs of the common horse bot
when the weather is cool will cause a high per-
centage of them to hatch. The young bots will
soon die when thus artificially hatched. The
water should be applied freely to the legs and
body where the eggs occur with a sponge or cloth
swab and rubbed vigorously.

This treatment is especially recommended
in conjunction with the internal treatment of
the animals with carbon disulphide. It should
be remembered that the eggs are ready to hatch
about 7 days after being laid and that the lar-
vae may remain alive within the eggs for about
3 months if they are not stimulated to hatch by
the contact of the horse's lips or by the method
mentioned above.

To bring about the best results in bot con-
trol the destruction of the eggs of the common
bot should be accomplished soon after the bot
flies have been killed by freezing weather in
the fall.

Treatment of Horses and I:ules for the Destruc-
tion of Bots

A high percentage of the bots in stomach
and duodenum can be destroyed by administering
carbon disulphide by mouth. The bots are killed

Circular 16 Horse Bots

by the drug in solution and as a gas. The treat-
ment also destroys most of the large intestinal
round worms.

This treatment is best given as early in
the winter as practicable, but it can be carried
out with a high degree of success any time from
December 1 to February 15.

A period of about 30 days should elapse
from the cessation of bot fly activity and the
application of hot water to the eggs before the
carbon disulphide is administered. This allows
time for the small bots that may be in the tis-
sues of the mouth to pass into the stomach where
they can be reached by the medication.

Carbon disulphide in liquid form is given
in gelatine capsules or in a masked capsule (ab-
sorbed on a neutral carrier and this powder
enclosed in a capsule). Another approved method
is through a stomach tube which insures getting
the material into the stomach.
The treatment recommended by the Bureau
of Animal Industry is as follows:

"Fast the animal from noon of the day pre-
ceding treatment until 6 or 7 o'clock of the next
morning. At this time the animal is given car-
bon disulphide in gelatine capsules, the capsules
being given by hand or by means of a balling gun.
The dose for a horse weighing about 1000 pounds
is 1 dose of 6 draas, or 2 doses of 4 drams each
with a 2-hour interval between doses, or 3 doses
of 3 dramns each with a 1-hour interval between
doses. Do not feed or water for 3 hours after
treatment. As a rule the single-dose treatment
is most satisfactory, but if there is any question
as to the animal's ability to tolerate the dose,
divided doses may be given and the treatment sus-

Circular 16 Horse Bots

pended if bad effects follow a partial treat-
ment. The dose should be diminished for smaller
animals, and yearling colts should not receive
over half the quantities given above. Very
old or weak horses, or those suffering from
febrile or debilitating diseases are sometimes
poor risks for treatment. The carbon disulphide
should not be followed by a purgative, and oil
is especially undesirable. Preliminary purga-
tion the evening before treatment is advisable
only in the case of a constipated animal. The
bots may continue to pass out for over two weeks
after treatment.

"In view of the fact that carbon disul-
phide is a poison, intended to poison the bots,
and one which may cause unpleasant results or
even death if given unskillfully or administered
to animals having disease conditions which make
the treat:Lent unsafe, it is always advisable to
have the treatment given by a coiipetent veterin-
arian whenever possible. Serious consequences
have resulted when poorly trained men used !iake-
shift balling suns.s '.-,hen a capsule breaks in a
horse's mouth and the carbon disulphide gets
into the lungs, the horse may- die."

The treatment of all horses, mules, and
donkeys in a given area is urged. This results
in a great reduction in bot fly annoyance the
following summer as well as in an irmwlediate im-
provenent of the treated animals.. All colts
dropped before the bot flies were killed by
cold weather are likely to be infested and should
be treated.

Circular 16 Horse Bats



F. C. and Dove, W. Z. 1926. The
horse bots and their control. U. S.
Dept. Agr. Farlers' Bull. 1503.

Dove, W. E. 1918. Some biological and control
studies of Gastrophilus haemorrhoidalis
and other bots of horses. U. S. Dept.
Agr. Bull. 597.



E. F. 1934. Observations on. first-
stage larvae of Gastrophilus intes-
tinalis in tongues of horses'-in Cen-
tral Iowa during December, 1932, and
January, 1933. Jour. Parasit. 20:
E. F. and Wells, R. W. 1935. Factors
stimulating hatching of eggs of Gas-
trophilus intestinalis De Geer and the
application of warna water as a practi-
cal method of destroying these eggs
on the host. Jour. Econ. Ent. 28:
1065-1072, illus.

Lowe, C. D. and Jones, M. P. 1932. Horse hot
flies and suggestions for organized
control. Extension Service. U. S.
Dept. Agr. (In process of revision.)
Schroeder, H. 0. 1940. Habits of the larvae
of Gastrophilus nasalis (L.) in the
mouth of the horse. Jour. Econ. Ent.
33: 382.
Wehr, E. E. 1933. Observations on the length
of time first-stage larvae of Gastroph-
ilus intestinalis remain in the tongue
of the horse. North Amer. Vet. 14(10):

Circular 16 Horse Bots 14

Wells, R. W. 1931. The method of ingress of
newly hatched larvae of the throat
bot of horses, Gastrophilus nasalis
(L.). Jour. Econ. Ent. 2-4: 1311.
Wells, R. W. 1938. A report of some recent
studies of species of Gastrophilus
occurring in horses in the United
States. Iowa State College Jour.
of Sci. 12(2): 181-203.


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