Parasites and Parasitic Diseases of Sheep. 15 
crawl out, conceal themselves in dry protected places, transform into 
adult ticks, and mate (fig. 8). The female lays eggs which give rise 
to the 6-legged seed ticks and these in turn infest new hosts. In- 
fested animals often have the ear canal plugged with wax and the 
excretions of the ticks. Such animals shake their heads or turn them 
from side to side. The ticks cause serious injury and occasionally 
death, especially among horses and cattle. The best treatment is to 
clean the ear canal with a wire loop, using care not to injure the ani- 
mal, and inject into the canal a mixture of 2 parts.commercial pine 
tar and 1 part cottonseed oil. 
The screw worm® is the name commonly given to the maggot 
of a sort of blowfly especially prevalent in the Southwest. It is 
especially apt to infest sheep 
recently sheared, getting into 
the fresh cuts, and in the same 
way attacks sheep and other 
animals that have been re- 
cently castrated, dehorned, or 
otherwise injured by having 
the skin broken. The fly is 
larger than the housefly (fig. 
9), dark bluish-green in color, 
with three black stripes on the 
back between the wings,’ and 
with a red or reddish-yellow 
colorimg in the face. It de- 
posits its eggs in carcasses or 
in wounds, in masses of from 
40 to 250 eggs. In wounds 
these eggs hatch in three hours 
or less, giving rise to young "Nich enlarged. (From Bishopd, Mitchell, 
maggots which burrow into and Parman, 1917.) 
the wound and grow rapidly 
during a period of 4 or 5 days (fig. 10). They then leave the 
wound, burrow into the ground and form pupe. The adult fly 
emerges from the pupal case in 3 to 14 days, the entire life cycle 
being 1 to 4 weeks. 
The best treatment for an infested wound is to pour in chloroform, 
later remove the maggots, wash with a suitable disinfectant, and 
apply pine tar to prevent fresh attacks. Probing and opening the 
burrows is regarded as inadvisable. When the wound is severe it 
is advisable to call in a veterinarian, as there is sometimes serious 
5 Cochliomyia macellaria (Chrysomyia macellaria). For additional information see 
Farmers’ Bulletin 857 on ‘“ Serew-Worms and Other Maggots Affecting Animals,” 
