36 CIRCULAR 148, U. S. DEPARTMENT OF AGRICULTURE 



The sucking louse of the horse is easily distinguished from the 

 biting species. It is much larger and has a long, pointed head, 

 whereas the biting lice have short, blunt, rounded heads. (Figs. 24 

 and 25. 6 ) The sucking louse apparently causes more damage than 

 the biting lice and it is more difficult to eradicate. 



NATURE AND HABITS 



The eggs or nits of the sucking louse are attached firmly to the hairs, 

 usually close to the skin, and they hatch on the animal in from 11 to 20 

 days, the majority hatching in from 12 to 14 days. The young lice 

 reach maturity and the females begin laying eggs when they are 11 or 

 12 days old. The lice pass their lives on horses, and can live only 

 about 2 or 3 days when off a host animal. 



The biting lice of horses deposit their eggs in the same general man- 

 ner as the sucking louse. The period of incubation is probably from 

 8 to 10 days. These lice may live as long as 10 days when separated 

 from the host animal if kept on tufts of hair, but most of them die in 

 5 or 6 days. 



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 remedies 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. 



/Sympto?ns. — The sucking louse obtains its food by puncturing the 

 skin of the horse and sucking blood and lymph. When not feeding 

 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 them- 

 selves, 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 irrita- 

 tion 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 is important to know whether the animals 

 are infested with biting or sucking lice or with both kinds. 



Method of spreading. — More cases of infestation originate from 



6 From photomicrographs by W. T. Huffman, of the Bureau of Animal Industry. 



