BIOLOGY AND CONTROL OF INSECT
AND RELATED PESTS OF HORSES
John E. Lloyd, Professor of Entomology
Everett W. Spackman, Extension Entomologist
Rabinder Kumar, Research Associate
University of Wyoming
Laramie, Wyoming
This material was prepared under Inter-Agency Agreement EPA-78-D-f-0473
between the University of Wyoming and EPA Region VIII Denver.

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Table of Contents
Introduction 	 1
Insecticide Use	 1
Precautions 		1
Insecticide Formulations 		2
Preparation of Correct Insecticide Concentration 		2
Dilution Table 		2
Formulas 		^
Methods of Insecticide Application 		^
Dilute Spray 		^
Mist Spray		^
Hand-Powered Sprayers 		^
Wash or Wipe-On		^
Residual Wall Spray 		7
Space Sprays or Aerosols		^
Dust		^
Biology and Control of Insects and Related Pests of Horses 	 7
Biting Flies and Nuisance Flies 	 7
Black Flies	 ?
Biting Midge 	 10
Mosquitoes	
Horse Flies and Deer Flies	12
Stable Fly	
House Fly	
Horn Fly	1^
Face Fly	15
Bot Flies	¦	1^
Control of Flies	'	16
Lice	18
Ticks		20
Winter Tick		20
Rocky Mountain Wood Tick	21
Spinose Ear Tick	21
Control of Ticks		22
Mange Mites	22
Sarcoptic Mange 		 23
Psoroptic Mange 		 23
Chorioptes Mange		r	24
Control of Mange	24
ii

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BIOLOGY AND CONTROL OF INSECT
AND RELATED PESTS OF HORSES
Prepared by
John E. Lloyd, Professor of Entomology
Everett W. Spackman, Extension Entomologist
Rabinder Kumar, Research Associate
University of Wyoming
Laramie, Wyoming
Introduction
The modern horse owner wants a
healthy and content animal, therefore
management of arthropod pests is
important. Many methods are available
to protect horses from the attack of
pests. When it becomes necessary to
use an Lnsecticide, it is important
that the most appropriate compound be
applied both safely and effectively.
In order to achieve the objectives
of this manual, the user should learn
three things: (1) recognition of
insect problems; (2) biological
features of the insects important in
their prevention and control; and,
(3) appropriate management techniques.
Recommendations of specific insecti-
cides are not presented. The reader
is urged to consult Agricultural
Experiment Station and Agricultural
Extension Service bulletins for
current insecticide recommendations.
When it becomes necessary to use
an insecticide, the label of the
appropriate formulation should be
read and understood. Be sure that the
formulation is approved for the
intended use. Some insecticide for-
mulations are for crop use only and
not for use on animals. When not in
use, all insecticides should be
placed in a proper storage area that
can be locked securely.
Before using the insecticide,
thoroughly familiarize vourself with
safe handling procedures, symptoms of
poisoning, if any, and what to do in
case of an accident.
Apply the insecticide in a manner
consistent with directions on the
insecticide label. If the compound is
not ready-to-use, then it must be
diluted to give the correct concen-
tration. Prepare only as much dilute
material as will be needed at one
time.
Insecticide Use
Precautions
Insecticides must be handled with
care because most are toxic to man and
animals as well as to insects.
Observe label precautions regard-
ing treatment of animals that for
reasons of health, age, condition, sex,
etc., may be adversely affected by the
treatment. Also, observe precautions
concerning use in conjunction with
other insecticides or with medication.
1

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Insecticide Formulations
Several different kinds of
insecticide formulations are avail-
able. Some, such as dusts, gels, or
oil solutions are ready-to-use,
directly from the original container,
while others, such as wettable powders
(WP) and emulsifiable concentrates
(EC) must be diluted prior to appli-
cation. Wettable powders are dry
concentrates that are formulated
with wetting agents so they will
disperse in water. Agitation of the
diluted material is necessary to keep
the insecticide in suspension.
Emulsifiable concentrate insecticides
also contain a high percentage of
active ingredient and must be diluted
prior to use.
Preparation of Correct Insecticide
Concentration
spray or dip liquid can be solved
rather easily with the help of a
dilution table or a formula as pre-
sented below.
Dilution Table
To prepare a spray or dip with a
desired percentage of active ingred-
ient, only the concentration of the
formulation need be known to use the
Table. The figures in the Table
represent the amount of pesticide
formulation for each 100 gallons.
For example:
A 0.03% concentration of lindane
is recommended for lice control on
horses. To make a 0.03% spray using
a 25% wettable powder (WP), the
Table tells us to mix 1 lb. of lindane
wettable powder in 100 gallons of
water.
Preparation of the correct con-
centration of insecticide is essential
for successful control. Errors in
determining the quantity of the
insecticide concentrate that must be
mixed with water or oil can result in
the use of excess toxicant that is
costly, and may lead to toxicity or
residue problems.
The concentration of insecticide
in wettable powders or emulsifiable
concentrates is found on the label.
The concentration of a wettable powder
is expressed as a percent, for
example, 25% malathion wettable powder.
The concentration of an emulsifiable
concentrate may be expressed as per-
cent active ingredient, or pounds of
active ingredient per gallon of
concentrate. For example, 11.6% Co-
Ral® (coumaphos) emulsifiable concen-
trate contains 1 pound of coumaphos
per gallon
The problem of determining the
quantity of wettable powder or emulsi-
fiable concentrate that will be needed
to prepare a certain volume of dilute
Formulas
Emulsifiable concentrates. - Two
different formulas may be used to
determine the amount of emulsifiable
concentrate needed to prepare a spray
or dip containing a given percentage
of active ingredient. In the first,
the concentration of emulsifiable con-
centrate is expressed as pound of active
ingredient per gallon. In the second,
the concentrate is expressed as percent
active ingredient.
gal	% active
spray X ingredient X (8.3)
wanted	wanted
ingredient/gal
of concentrate
or,
% active ingredient in concentrate
% active ingredient wanted
number of parts of finished
spray or dip that must
contain 1 part of the
concentrate
2

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DILUTION TABLE
Percentage of actual chemical wanted
Formulation	0.0313%	0.0625%	0.125%	0.257,	0.5%	1.0%






Wet table
Powder
(WP)






15% IvP
1 2/3
lb
3
1/3
lb
6 2/3
lb
13
1/3 lb
26
2/3
lb
53
1/3
lb
25% WP
1
lb
2

lb
4
lb
8
lb
16

lb
32

lb
40% WP
5/8
lb
1
1/4
lb
2 1/2
lb
5
lb
10

lb
20

lb
50% WP
1/2
lb
1

lb
2
lb
4
lb
8

lb
16

lb
75% WP
1/3
lb

2/3
lb
1 1/3
lb
2
2/3 lb
5
1/3
lb
10
2/3
lb






Emulsifiable
Concentrate (EC)






1 lb actual/gal















(10-12% EC)
2
Pt
4

Pt
1
gal
2
gal
4

gal
8

gal
1.5 lb actual/gal















(15-20% EC)
1 1/2
Pt
3

Pt
6
Pt
1
1/2 gal
3

gal
6

gal
2 lb actual/gal















(25% EC)
1
Pt
2

Pt
4
Pt
1
gal
2

gal
4

gal
3 lb actual/gal


«*












(33-357. EC)
3/4
Pt
1
1/2
Pt
3
Pt
6
Pt
1
1/2
gal
3

gal
4 lb actual/gal















(40-50% EC)
1/2
Pt
1

Pt
2
Pt
4
Pt
1

gal
2

gal
5 lb actual/gal















(57% EC)
7/16
Pt

7/8
Pt
1 3/4
Pt
3
1/2 pt
7

Pt
1
3/4
gal
6 lb actual/gal















(60-65% EC)
3/8
Pt

3/4
Pt
1 1/2
Pt
3
Pt
6

Pt
1
1/2
gal
3 lb actual/gal
1/4
Pt

1/2
Pt
1
Pt
2
Pt
4

Pt
1

gal
lb = pounds
pt = pints
gal = gallons

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For example:
How many gallons of 25% lindane
(2 lb./gal) emulsifiable concentrate
are needed to make 100 gallons of
spray containing 0.25% lindane?
Using 2 lb. active ingredient/gal
(100) X (0.25) X (8.3) =
(2) X (100)	8
or,
Using 25% active ingredient
25% = 100
0.25%	1
The dilution is one part 25%
lindane in 100 parts of finished
spray or dip. This would be equiva-
lent to 1 gallon 25% lindane to 99
gallons water.
Wettable powders. - The follow-
ing formula is used to determine the
pounds of wettable powder needed to
prepare a spray or dip containing a
given percentage of active ingredient.
gal	% active
spray X ingredient X (8.3)
wanted	wanted	
(% active ingredient in WP)
For example:
How many pounds of lindane 25%
wettable powder are needed to make
100 gallons of spray containing 0.03%
lindane?
(100) X (0.03) X (8.3) = 1 lb.
25
Methods of Insecticide Application
Application techniques commonly
utilized in the control of several
different pests are discussed here.
More specific information is presented
later along with the individual pests.
The purpose is to familiarize the
reader with common application tech-
niques and terminology.
Dilute Spray
Diluted insecticide may be applied
by means of a livestock sprayer (Figure
1). Such a sprayer will provide the
pressure necessary for penetration of
a hair coat. An obvious disadvantage
of the method is that horses may be
upset by the noise of the sprayer as
well as the pressure of the spray.
It is important to calibrate the
sprayer. Determine the delivery in
gallons per minute for the particular
spraying disc in the spray gun and the
pressure. The amount of spray per
animal will vary with size of animal,
and thickness of hair coat due to time
of year.
Mist Spray
An electric mist applicator may
be used to apply small quantities of
relatively concentrated insecticide
spray (Figure 2). A large nozzle size
is desirable for a coarser spray that
will adhere to the hair coat of an
animal. Some horses will react to the
noise of the sprayer.
Hand-Powered Sprayers
An easy method of spraying a few
animals is with small, hand-powered
sprayers (Figure 3). These sprayers
make little noise arid usually do not
frighten horses.
Wash or Wipe-on
An ordinary sponge, cloth or
special glove made for this purpose
(Figure 4) may be used to wine
4

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Figure 1. A livestock sprayer.
Figure 2. An electric mist applicator.
Figure 3. Small, hand-powered sprayers.
5

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Figure 4.	Wash or wipe-on insecticide.
a.	Sponge
b.	Special glove.
c.	Wipe-on salve.
6

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insecticidal gels and liquids onto the
horse's body. When not using the
special glove-applicator, be sure to
wear other protective gloves. This
method may be used to apply insecti-
cides to horses that react to sprayer
noises.
Residual Wall Spray
Wall sprays are applied at low
pressure to produce a coarse spray.
Spray may be applied to fences, inside
and outside walls of buildings (Figure
5) with care to avoid spraying feed
and water. Horses and other animals
should be removed from buildings prior
to spraying.
Space Sprays or Aerosols
This is a method for quickly
clearing spaces of flying insects.
A machine (Figure 6) is used that
produces a very fine mist or fog that
remains suspended in the air for
several hours. The application is
most effective indoors and must be
repeated frequently.
Dust
Horses may be individually treat-
ed with insecticide dust. The dust
may be applied by shaker can or other
means (Figure 7).
Biology and Control of Insects and
Related Pests of Horses
Biting Flies and Nuisance Flies
Flies are familiar to everyone.
Biting flies are blood-sucking
insects that are particularly bother-
some to horses. They include stable
fly, horse flies, deer flies,
mosquitoes, biting midges and black
flies. Face fly and house fly are
nuisance flies. They are very
bothersome even though they do not
bite and draw blood. Bot flies do
not bite, but their egg-laying
habits are very annoying and larval
bots are important internal parasites.
Both biting and nuisance flies
affect the behavior of horses. Flies
will hinder grazing and resting,
and even force horses to run about in
order to be momentarily freed from
annoyance. In addition, many flies
are important in transmission of
disease causing organisms.
Black Flies
There are many species in the
black fly family Simuliidae, and they
are among the smallest of the biting
flies that attack horses. Frequently,
they are called buffalo gnats because
of their "humped back" appearance.
Black fly may be a misnomer because
some species that attack horses are
frequently tan or yellowish in color.
larva
Figure 8. Life stages of a black fly
The adult of this species is approx-
imately 3.5 mm.
7

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Figure 5. Residual wall spray.
Figure 6. A mist applicator (6a) and a fogger
(6b).
8

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Figure 7a. Hand dusting a single animal.
7b. Application of dust to the ear.
9

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The four life stages of the
black fly are illustrated in Figure 8.
The duration of the life stages varies
considerably with the different
species. Several hundred eggs may be
deposited on or in the water by the
adult female. Larval and pupal
black flies spend their lives in
rivers, canals, or streams where
fresh, running water provides suffi-
cient aeration. These aquatic stages
are attached to objects such as
stones, logs and submerged vegetation.
After emergence, the adult flies are
capable of moving considerable dis-
tances from the waters of their
origin.
Figure 9. The life stages of
Culicoides variipennis, a biting
midge. The adult is approximately
2 mm.
Female black flies are attracted
in large swarms to the host animal.
They fly about and get into the nose,
eyes, ears and mouth. They feed
either on exposed areas of skin or
deep within the hair coat. They
lacerate the skin and suck oozing
blood. Strong anticoagulants in the
saliva prevent coagulation of the
blood for some time after the bite.
A large, painful welt may develop at
the site of the lesion.
Some black fly species that are
serious pests of horses prefer to feed
on animals. Black flies significantly
affect the performance of horses, and
during severe outbreaks, death losses
have been reported.
Biting Midge
The very tiny, bloodsucking
midge or gnat, Culicoides variipennis
(Family: Ceratopogonidae), is a
common pest of horses (Figure 9).
Swarms of these midges may attack,
primarily in the evening. Large
numbers may be responsible for sores
and scabby areas along the belly of
horses.
Ideal larval breeding sites for
C!. variipennis usually consist of
non-vegetated, open areas of soft,
silty mud,'exposed to direct sunlight.
Such areas may be found in natural
marshy areas or along the margins
of alkaline bodies of water in the
West. Very dense populations of
larvae can occur as a result of
pollution by livestock or human wastes,
e.g., near feedlots or inadequate
human sewage facilities.
Mosquitoes
Adult mosquitoes are small (body
length about 6 mm or less) delicate
organisms with a conspicuous long
snout or proboscis. Mosquito life
stages are egg, larva, pupa and
adult. The eggs are laid on or near
water. When in contact with water the
eggs hatch and produce the aquatic
immature stages. The larvae or
"wigglers", with very few exceptions,
are found in standing water with rela-
tively little movement or wave action.
In the larval stage the mosquito
attains most of its growth. After
four larval stages of increasing size,
10

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larvae molt to the pupal stage. The
pupa or "tumbler" moves about in the
water by a tumbling action. After a
few days, the pupa moves to the
surface of the water, and the adult
mosquito emerges from a slit in the
"back".
Usually, adult males emerge
first and remain near the larval
habitat and fertilize females shortly
after their emergence. Most fer-
tilized female mosquitoes then require
a blood meal before egg-laying.
Female mosquitoes of the genera
Aedes and Culex are among the serious
pests of horses. Examples of the two
genera are presented in Figure 10.
Note that these can be distinguished
by the shape of the tip of the
abdomen.
species will readily feed during the
daylight hours.
The life cycle of a typical
Aedes mosquito is presented in Figure
11. The eggs are laid on moist soil
in areas subject to reflooding, and
where the females are somewhat pro-
tected from the wind. The eggs may
survive for several years before
flooding. In temperate areas, Aedes
mosquitoes overwinter in the egg stage,
then hatch in the spring due to spring
runoff or irrigation. Repeated flood-
ing through the warm months will
produce additional broods of some
species.
0'-
Figure 10. Female mosquitoes of two
genera. The tip of the abdomen is
pointed in Aedes and blunt in Culex.
These specimens are approximately
5-6 mm.

Pupae or tumblers
Lorvoe or wiggtert
Figure 11. The life cycle of Aedes.
Aedes or flood-water mosquitoes
are extremely important pests
because there are many species, and
they appear in tremendous numbers.
They are produced in vast inundated
areas such as marshes, flood plains,
snow pools and irrigated meadows.
The adult females are avid feeders on
both man and his animals. While
most bites occur during the early
morning and evening hours, some
Culex mosquitoes will feed on
horses, and in the West, Culex tarsalis
is the important vector of Western
Equine Encephalitis. The life history
of Culex (Figure 12) differs from
that of Aedes. The eggs are deposited
on the surface of standing water in
groups called "rafts", and they hatch
shortly thereafter. These mosquitoes
are able to utilize many different
11

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kinds of standing water, fresh or
polluted, usually in open, sunlit
locations. Examples of suitable habi-
tats are ponds, ditches, puddles in
corrals, and artificial containers
such as poorly maintained stock tanks
or discarded drums, barrels and cans.
These mosquitoes overwinter in sheltered
locations as hibernating adults.
Figure 12. The life cycle of Culex.
Horse Flies and Deer Flies
Horse flies and deer flies belong
to the same insect family, the Tabani-
dae, and are similar in many ways.
Many species of horse flies and deer
flies attack horses and three are
illustrated in Figure 13. Deer flies
are usually about the same size or a
little larger than the ordinary house
fly, and frequently have distinct
patterns on their wings. Horse flies
are larger and darker than deer flies.
Some are quite large.
Adult horse flies and deer flies
usually appear in large numbers at
certain times during the season.
Females attack animals, and the bite,
which is extremely painful, causes
considerable flow of blood. Fre-
quently, clusters of other kinds of
flies will surround pools of blood
formed by the feeding of horse flies.
Cftrysops
Ote> fly
Tabanut
Horw fly
Tatunuj
Haru fty
Figure 13. Adult deer fly and horse
flies. These specimens range in size
from 9-28 mm.
The life stages of a horse fly
are presented in Figure 14. The
female flies lay their eggs, often
attached to vegetation, near the
damp or wet soil of streams, marshes,
lakes or ponds. After a short incu-
bation period of approixmately 1 week,
larvae hatch, then develop in
water or wet soil. Later in the
season or possibly the following year,
full grown larvae migrate to drier
soil. Each forms a pupal case, from
which an adult fly will eventually
emerge.
vyt —
/"N
V X
U^7
egg moss
krvo
Figure 14. Life stages of a horse fly.
12

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Stable Fly
The stable fly, Stomoxys calci-
trans, looks much like a house fly
except that it has a prominent beak
(Figure 15).
stable fly can produce several
generations per season.
Figure 15. The adult stable fly,
and enlarged side-view of head and
piercing mouthparts. The specimen
is approximately 8 mm.
Eggs of the stable fly are
deposited in wet and decaying organic
matter. Wet feed and hay contami-
nated with manure, urine and mud are
particularly good media for develop-
ment of stable fly larvae or maggots.
In areas where bodies of water occur,
stable fly may be abundant because
piles of decaying "seaweed" are good
larvae media.
The life stages of the stable
fly are presented in Figure 16.
After egg hatching, the larvae pass
through three larval stages. After
the final larval stage a pupnl or
inactive stage is formed. Eventually
an adult fly emerges from the pupal
case. Because of rapid development
from egg to adult, about 24 days,
Adull
Mi

Eqqs
Pupa
\
/
3rd Stage
Larvo
Figure 16. The life stages of the
stable fly.
Both male and female stable
fly readily attack horses. They have
a stout proboscis with which they
pierce the skin and suck blood. The
bite is painful. Stable fly is a
vector of the worms responsible for
"summer sore" of horses.
Stable fly is a particularly
serious problem in areas where there
is suitable medium for production of
larvae. Such conditions frequently
exist in and around livestock build-
ings and lots where stable fly can be
found indoors as well as out.
House Fly
The house fly, Musca domestica,
'is a widespread pest that is familiar
to everyone. Though it does not
13

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inflict a painful, bite because of the
nature of its mouthparts (Figure 17),
it is a very annoying insect and a
potential vector of many disease-
causing organisms of man, but also
parasites of horses such as stomach
worms.
/
\
Pupa
\
Mm
Eggs
/
3rd Stage
Larva
Figure 18. The life stages of the
house fly.
Figure 17. The adult house fly, and
enlarged side-view of head and pierc-
ing mouthparts. The specimen is
approximately 7 mm.
The four life stages of the house
fly, egg, larva, pupa and adult are
presented in Figure 18. The complete
life cycle requires only two weeks
in warm weather.
The house fly is a pest closely
associated with man's activities. It
is able to utilize many kinds of
organic matter, such as found in
garbage, as a larval medium. It is
also able to utilize all sorts of
decaying excrement. Primarily, it is
considered a pest in and around
livestock buildings and feedlots.
Horn Fly
The adult horn fly, Haematobia
irritans, looks much like a miniature
stable fly. It is primarily a pest
of cattle but will also attack
horses. Both sexes have beaks which
they utilize to obtain blood meals.
The horn fly may reach very large popu-
lations on animals.
fly is approximately A mm.
14

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Ordinarily the flies congregate
on the shoulders and sides of the
animal. During extremely hot sun-
shiny or rainy weather the flies con-
gregate on the underside of the belly.
The adult female deposits eggs
in fresh cattle droppings. Larval
development occurs in the dung pat.
horses at all times and do not enter
darkened barns or stables. The adult
face fly passes the winter in the
adult stage within shelters and may
be a household pest in the spring
when the flies emerge from their
indoor hibernation quarters.
Bot Flies
Face Fly
The face fly, Musca autumnalis,
is an important, nuisance-type fly
affecting horses. The insect looks
very much like the house fly. In
fact, it is very difficult to distin-
guish the two except in the pupal
stage which is red in the case of the
house fly and white for the face fly.
Figure 20. The face fly.
is approximately 8 mm.
The adult
The face fly is primarily a
pest of cattle, but it also annoys
horses. It has the habit of land-
ing on the face and probing the eyes
and nostrils.
The life stages of the face fly
are egg, larva, pupa and adult
(Figure 18). The adult female face
fly lays its eggs in fresh cattle
droppings. Development occurs only
in fresh, undisturbed droppings such
as those on pasture.
The face fly is a strong flier
and can travel several miles. Indivi-
dual face flies do not remain with
In the U.S. three species of
bot flies infest horses. Two of
them, the nose bot fly, Gasterophilus
haemorrhoidalis, and the throat bot
fly, Gasterophilus nasalis, have
received common names based on the
egg-laying habits of the female flies.
The third species, Gasterophilus
intestinalis, is simply called the
the horse bot fly. Adult bot flies are
rather large flies (Figure 21) which
frequently are seen laying eggs on
horses. The larval or bot stage
is attached to the lining of the
stomach (Figure 23) or the intestines.
Figure 21. The horse bot fly.
adult is approximately 15 mm.
The
Horse bots cause injury in several
ways. Since the mouthparts of the adult
flies are non-functional, they cannot
bite. However, the egg-laying habits of
15

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flies annoy or terrorize the horses
and cause them to mill or run, thus
interfering with work and grazing.
Because of this annoyance, horses may
lose weight and vitality. Also, young
larvae or bots penetrate and irritate
submucosal tissues of tlie inner lip,
mouth, and tongue; and induce horses
to rub their mouths on hard objects,
causing additional sores. Older
larvae attach to the lining of the
stomach and intestines, removing
nutrients and causing inflammation.
Heavy infestations hinder passage
of food through the ailmentary canal
and impair digestion of food.
Horse bot fly. - The life cycle
of the horse bot fly is illustrated
in Figure 22. Female common horse
bot flies may lay up to 1,000 eggs.
The eggs are usually attached to
the hairs of the forelegs or in other
places the horse can reach with its
mouth.

Figure 22. Life cycle of the horse
bot fly.
After a five day incubation
period, heat caused by licking of the
horse stimulates the eggs to hatch.
Young larvae are taken into the
mouth, where they burrow in the
mucous membrane of the tongue.
After three or four weeks in the
subepithelial layer of the mucous
membrane of the tongue, the larvae
pass to the stomach where they attach
to the lining and pass their lives
as second and third larval stages. The
larvae remain in the stomach for 10
months until the following spring when
they pass out with the feces. Pupation
takes place in loose soil or ground
litter. The pupal period lasts from
three to five weeks. Individual
adult flies may live, for about three
weeks. Larvae continue to drop from
the host over a long period of time,
and flies can be found annoying
horses from late summer into early
fall.
Nose bot fly. - The eggs of the
nose bot fly, which are laid mainly
in the hairs of the upper lip, require
an incubation period of approximately
two days. Moisture provided by lick-
ing may be necessary for hatching. The
larvae penetrate the lips and migrate
into and invade tissue of the mouth.
This species moves to and attaches to
the stomach and duodenum in the second
and early third larval stage. Unlike
the other species, it then detaches and
reattaches in large numbers in the
rectum, very close to the anus, before
dropping out with the feces. The
rest of the life of the nose bot fly is
similar to that of the other horse
bot flies.
Throat bot fly. - Eggs of the
throat bot fly, which are attached to
hairs of the lower jaw of the horse,
apparently require no stimulus to
hatch. One female can lay from 300
to 500 eggs. Within six days after
egg-laying, newly hatched larvae
migrate to the lips, then into the
tissue lining the mouth. After three
to four weeks they move back to the
pyloric portion of the stomach and the
anterior portion of the duodenum. The
rest of the life cycle is similar to
the other two species.
Control of Flies
If facilities are available, it
may be advisable to provide shelter
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from the attacks of the various flies.
Use of fly screens on windows may
be necessary.
Temporary protection of horses
from flies is possible through
frequent applications of fast-acting
insecticides or insecticide-repellent
combinations. Various sprays and
wipe-ons may be used. This is prac-
tical only if animals can be handled
frequently.
Much can be done to alleviate
house fly and stable fly problems
around livestock buildings and
feedlots through sanitation and
proper management of manure. Basi-
cally this means elimination of
larval habitat or modification in
such a way as to make it unsuitable
for fly production. Prompt and
regular removal and dispersal of
manure, soiled bedding and spilled
feed is a good fly preventive
measure, as is elimination of wet
areas in paddocks and lots.
Insecticide-based control is
possible when a fly problem gets out
of hand around livestock buildings.
Residual sprays, applied to walls,
ceilings, fences and other favored
resting places are effective and may
last several weeks. For fly control
in buildings various insecticide
baits are effective against house fly
if used properly. For fast but
temporary control of flying insects
in confined areas, fogs, aerosols
or mist applications are effective.
Out-of-doors, mist applications
that involve a finely divided spray
will disperse quite rapidly. The
dispersed droplets kill only the
flies they contact. This method,
including ground and aerial applica-
tion, can be used, however, for
temporary reLief from a serious out-
break of biting flies.
Many populations of the biting
midge, Culicoides variinennis are
produced inadvertently on farms and
ranches, and may be eliminated through
management or cultural practices.
Examples of such larval breeding sites
are: sites where water-borne human
sewage flows out onto the ground;
puddles contaminated with manure
such as those that occur near water
tanks and in livestock pens; and dirt
stock ponds where manure has been
trampled into the shallow water along
the edge.
Mosquito annoyance may be reduced
through source elimination, i.e.,
elimination of the water that provides
a suitable habitat for mosquito
larvae. Mosquito larvae can also be
eliminated through the removal of
protective emergent vegetation from
irrigation ditches and the edges of
ponds and lagoons.
In several locations, communities
as well as smaller groups of farmers
and ranchers have organized for
mosquito control. Primarily these
programs have involved aerial appli-
cation of larvicides to vast areas of
flooded land.
Chemical control of hot flies is
directed against the larvae attached
to the lining of the stomach and
intestines. A number of chemicals
that are available for control of bots
will also control parasitic worms.
Some drugs and formulations for bot
control are restricted by law to use by
or on the order of a licensed
veterinarian.
One of the simplest control
techniques is the feeding of an
approved insecticide feed additive
(Figure 23). This material is mixed
with the amount of feed to be consumed
at one feeding. Gel and paste formu-
lations are also available and easier
to use when horses find the feed
additive unpalatable. The products are
available in pre-filled syringes,
ready to administer directly onto the
back of the tongue.
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a b
Figure 23 a.	Horse bot larvae attached to stomach lining.
b.	Insecticide feed additive.
c.	Insecticide feed additive.
d.	Insecticide paste.
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Larvae of the horse hot fly may
be destroyed by rubbing the legs,
under the jaw, and the chest of all
horses that bear eggs, with water
heated to the point at which one's
hand can be immersed without dis-
comfort. The heat from the water
stimulates the eggs to hatch and the
new larvae die quickly.
For most effective bot control
all horses, mules and donkeys in an
area should be treated. In this way,
a substantial reduction of the flies
may be brought about the following
summer
Lice
Horses may be infested with the
horse-sucking louse, Haematopinus
asini (Figure 24), or the horse biting
louse, Bovicola equi (Figure 25).
4^
Figure 24. The horse sucking louse.
Up to 3.5 mm.
Louse populations are most
numerous and most severe in the winter.
This is also the time of year when the
animals are under additional stress
due to cold weather and poorer nutri-
tion. The combination can produce an
unhealthy, anemic, and unthrifty
horse. The horse-sucking louse is
irritating and is important because
it feeds by sucking blood from the host.
The biting louse feeds by gnawing at
scurf and hair.
Figure 25. The horse biting louse.
Between 1.5 and 2 mm.
There are three stages in the
life history of horse lice (Figure 26).
They are: (1) the egg or nit stage,
which is attached to the hair of the
host animal, (2) the nymphal or
immature stage, which consists of
three instars or growth stages of
increasing size, and (3) the adult
stage. The lengths of various life
stages of lice vary, being one to
two weeks for eggs, two to three weeks
for nymphs, and two weeks or longer
for adults.
Figure 26. The life cycle of a louse.
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Horse lice are host specific like
most other lice of domesticated ani-
mals. They are only pests of closely
related hosts such as horses, inules
and asses. Lice spend their entire
lives on their host animals and
spread from one animal to another in
close contact.
Horse lice are easy to control
with many different spray materials or
a dust. Remember that an animal that
has not been sprayed may reinfest a
herd.
Figure 27. The winter tick. The
unengorged female is A.5 to 5.0 mm.
Ticks
Frequently horses become infested
with ticks. Ticks are not insects,
and do not resemble them. Ticks as
well as mites are more closely related
to spiders, scorpions, etc. Ticks
have four developmental stages: egg,
larva, nymph, and adult. The larvae,
nymphs, and adults can be differen-
tiated according to size. Larval
ticks possess six legs, whereas
adults and nymphs have eight.
Ticks are obligatory parasites
and require blood meals in order to
develop. The tick feeds by driving its
mouthparts into the skin of the host.
The feeding of ticks produces wounds,
and removes large quantities of blood.
Some ticks transmit disease organisms
or causes paralysis in livestock.
Winter Tick
The winter tick, Dermacentor albi-
pictus (Figure 27) is a frequent a~n3
widespread pest of horses. Preferred
hosts are horses, moose and elk.
Young animals are especially vulner-
able to attack and may be killed by
heavy infestations.
This tick is a pest in the fall,
winter and early springs of the year.
The larval or seed ticks, which are
similar to the adults except for
smaller size and possessing six
legs, spend the summer in clusters on
the ground. When the cool weather of
fall approaches, the larval ticks
become active and seek a host.
The tick remains on and feeds on the
blood of the same host throughout
its life (Figure 28). For this reason
the winter tick is called a "one-host
tick". The mated, fully blood-engor-
ged female tick drops off the host
in early spring. Egg laying takes
place on the ground later in the
spring.
Figure 28. Life cycle of the winter
tick.
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Rocky Mountain Wood Tick
The Rocky Mountain wood tick,
Derinacentor andcrson L (Figure 29) ,
attacks most domesticated animals.
In addition to being very pestiferous,
toxins secreted by the female tick
can paralyze many animals including
man and horses.
Figure 29. The Rocky Mountain wood
tick." The unfed female is about 5 mm.
Rocky Mountain wood ticks may
cause tick paralysis in livestock by
the feeding of females and their
injection of a toxin into the blood
stream of the host. First symtoms
of afflicted animals are weakness and
staggers. In a few hours they are
incapable of standing, and finally
deatli ensues. Animals can be saved
by removing the offending ticks.
Recovery may be rapid (within an hour)
or it may take a couple of days.
When recovery does not occur within
this time, it is an indication that
some ticks may have been overlooked
in the removal.
The Rocky Mountain wood tick is
a "three host tick" and has a com-
plicated life cycle (Figure 30).
It is a problem in the spring of the
year when adults come out of hiberna-
tion. They climb upon vegetation, and
wait to attach to a suitable large
manmal host passing by. Mating and
feeding occur on the host with the
female dropping off the host in about
one to three weeks. Egg-laying
takes place on the ground in a shel-
tered location. Over 6,000 eggs can
be produced by one female. The larval
or seed ticks hatch in a month. These,
if fortunate, attach to a small wild
mammal host where they feed for a
period of two to eight days, then
drop off. Nymphs appear three weeks
after the larvae drop. At this time
they may either hibernate that winter
as nymphs or find another small
mammal host. If another host is
found, the tick feeds, drops off, and
molts; then spends the winter as an
unfed adult. Overwintering nymphs
seek small mammal hosts the following
summer, feed for about a week, drop off
the host, molt and overwinter as unfed
adults.
UMM ^/[Sv	
f«male	vnoll mommoi
j\	Adull	&
l V !^IS,,n,ole	1
A	wncll mommoi
Blood erqorqed	m
femoit	f
Egg most
Figure 30. Life cycle of the Rocky
Mountain wood tick.
Spinose Ear Tick
The spinose ear tick, Otobius
megnini, is a serious pest of many
species of domesticated and wild
animals. It is considered primarily
a pest in warmer climates, but has
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become locally established in some
more temperate regions. The larvae
and nymphs oC this species are
found in the ears of horses, cattle,
sheep, dogs, cats, deer, rabbits and
numerous other domesticated and wild
animals. They are abundant during the
summer months.
The nymphs and larvae (Figure 31)
of this tick cause injury by punc-
turing the tender skin within the
ear and sucking blood. Wounds may
become infected with bacteria. Plugs
formed by accumulation of ticks, their
excretions, and ear wax may block the
ear passage completely. A tendency
for the animal to rub and scratch
affected ears may result in extensive
lacerations.
After attaching to the host, the
larval tick moves to the ear where
it attaches to the delicate lining of
the ear and engorges. It molts in one
to two weeks to the nymphal stages,
which may remain in the ear up to
six months. Nymphs then drop to the
ground, molt to the adult stage,
mate and lay eggs.
Control of Ticks
If ticks become attached, the
simplest method of removing them is
by a slow steady pull that will not
break off the mouthparts and leave
them in the wound. An antiseptic
should be applied to tick bites as to
other open wounds.
Figure 31. Life cycle of the spinose
ear tick. The engorged larva and
nymph, which are found in the ear, are
approximately 3.5 and 7.5 mm, res-
pectively .
The life cycle of the spinose
ear tick is complicated. It is a
one host tick, meaning that all para-
sitic stages of any individual tick
remain on one host. Larval ticks
hatch from eggs that have been laid
on the ground. The larvae climb onto
weeds, vegetation, and feeding
troughs to contact host animals.
Thorough coverage of an infested
animal is necessary for insecticidal
control of the winter tick and the Rocky
Mountain wood tick. Several different
insecticides are approved for this
purpose. Application may be by means
of spray, dip or hand-washing. For
control of the spinose ear tick, dust
or oil solution formulations must be
applied directly into the ears of
infected animals.
Mange Mites
Several different mite species
produce a contagious disease of the
skin of various domestic animals
known as mange. The type of mange
is named after the mite causing it,
e.g. sarcoptic mange, psoroptic mange,
and chorioptic mange of horses which
are caused by Sarcoptes scabiei,
Psoroptes ovis and Chorioptes bovis,
respectively.
All three mite species mentioned
have developmental stages similar
to those of ticks, i.e. eggs, six-
legged larvae, eight-legged r.ymphs,
and eight-legged adults (Figure 32).
Mites are microscopic in size and
barely visible to the naked eye.
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Specific identification should be made
by a trained individual. The symptoms
of the disease are quite obvious,
however, and may consist of blisters
and small bumps in the skin, swelling
and inflammation of the skin, scabs
which consist of serum and scurf, and,
in advanced cases, a dry, leathery
skin condition.
on the head, neck and shoulders, then
spread to other parts of the body.
Figure 32. The life cycle of a mange
mite.
Mange is highly contngious.
Mange mites are transmitted by con-
tact with infected animals or equip-
ment. Populations are generally
greatest in the winter when hair
coats are long and horses are crowded
together.
Sarcoptic Mange
Sarcoptic mange is the most
severe type in horses. Adult sarcoptic
mites (Figure 33) burrow within the
skin of the host and cause severe
irritation. Eggs are laid within the
burrows. Development of the mite
from egg to reproductive adult takes
approximately two weeks. Lesions
usually, but not always, first anoear
Figure 33. Sarcoptes scabiei, a
mange mite. Microscopic in size.
As the horse scratches to relieve
irritation, blisters and small bumps
or ridges develop on the skin.
Further scratching causes the blisters
to break, forming scabs. In advanced
cases the affected skin becomes
dry, wrinkled and hairless, and
remains so for some time.
Psoroptic Mange
Psoroptic mange of horses (caused
by Psoroptes £vis), is a notifiable
and quarantinable disease, but it has
not been reported in horses in the
United States for at least 30 years.
The life cycle of Psoroptes ovis
(Figure 34) takes about two weeks.
The habits differ from those of
sarcoptic mites, however. Psoroptic
mites do not burrow in the skin of the
host. Instead, by pricking the skin
to feed, they cause serum to ooze from
the wounds. Accumulation of serum
causes the formation of scabs which
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start on the hairier parts of the body
such as under the mane or at the base
of the tail. Infestations eventually
may involve large areas of skin all
over the body.
Figure 34. Psoroptes ovis, a mange
mite. Microscopic in size.
Chorioptes Mange
Chorioptes mites (Figure 35)
have life cycles similar to Psoroptes.
Chorioptic mange is also called "leg
mange" because cutaneous lesions
are found mainly on the lower parts
of the hind legs.
Figure 35. Chorioptes bovis, a mange
mite. Microscopic in size.
Control of Mange
Dipping, thoroughly spraying, or
hand-washing, are the only treatments
for mange control.
* U. S. GOVERNMENT PRINTING OFFICE 1980 680-144/72 Reg. 8
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