36 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 
During cold weather, when the hair on horses is long, lice increase 
very rapidly; but when the animals shed their hair in the spring 
the parasites seem to disappear. Some of the lice usually remain 
on the animals throughout the summer, but not in sufficient numbers 
to cause annoyance or to be easily detected. The animals, therefore, 
usually go into the winter infested. Since the most efficacious rem- 
edies are liquid dips, which can not be used safely on horses during 
cold weather, fall dipping should be practiced whenever horses have 
been lousy at shedding time. 
Symptoms.—The sucking louse obtains its food by puncturing the 
skin of the horse and sucking blood and lymph. When not feed- 
ing it moves about on the hair and skin. The biting lice do not suck 
blood from the host, but apparently feed on particles of hair, scales, 
and exudations from the skin. The irritation and itching which 
result from either or both methods of feeding are shown by the 
efforts of infested animals to obtain relief. Infested horses rub and 
bite themselves, and often kick and stamp and manifest extreme 
uneasiness and irritation. 
The coat becomes rough; the frequent rubbing destroys the hair 
in patches and often causes bruises or wounds in the skin. If lice 
are present in sufficient numbers to cause considerable itching and 
irritation they can usually be found, especially if the infested animal 
is placed in the sunshine. All species of horse lice are easily seen 
with the naked eye and often congregate in groups or colonies on 
parts of the animal. The favorite locations are the sides of the 
neck, around the flanks, and under the jaws. In cases of gross 
infestation, however, lice may be found all over the body and legs. 
When horses are lousy, close examination should be made to learn 
what kind or species of lice is present. It is not especially impor- 
tant, from a practical standpoint, to distinguish between the two 
species of biting lice, but it 1s important to know whether the ani- 
mals are infested with biting or sucking lice or with both kinds. 
Method of spreading—More cases of infestation originate from 
direct contact with lousy animals than in any other way. Under 
reasonably good sanitary conditions stables, yards, and other prem- 
ises which have contained lousy horses are not a source of great 
danger to horses free from lice. It seems probable, however, that 
occasionally lice may become dislodged from their host and drop on 
mangers, floors, etc., and from these locations find their way to a new 
host. 
When separated from their host sucking lice live about three days, 
the biting lice not to exceed 10 days. Ordinarily eggs are not de- 
posited except on the host, but when the hair to which they are 
attached is removed and kept under favorable conditions they may 
continue to hatch for as long as 20 days. The newly hatched lice 
live only two or three days unless they find a host. It is therefore 
possible for premises to remain infested for 25 or 30 days from the 
time they were occupied by infested horses. When lousy horses are 
clipped the hair should be burned and the ground or floor where the 
clippings dropped should be thoroughly treated with an insecticide. 
Lice may be carried from one animal to another on currycombs, 
brushes, and blankets, or by harness, saddles, and other equipment 
moved directly from a lousy horse to one free from lice. Curry- 
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