144 THE HORSE-TICK. 
Here they insert their beaks to draw blood. It seems that 
they irritate the infested animals more by their running over 
them than by the absorption of blood, though they must. 
also cause pain. Horses attacked by such tormenters be- 
come very restless, even dangerous and unmanageable. As 
the insects are very active they are not very easily captured, 

Fig. 124.—Louse-fly from Grossbeak. Greatly enlarged. Original. 
for they either fly away or cling so firmly to the skin that 
they can not be removed without difficulty, nor can they be 
crushed, as they are well protected by a very smooth and 
exceedingly tough skin. If these parasites escape, after hav- 
ing been captured, they are apt to return instantly to the 
horse; but as mistakes are not impossible they have been 
known to invade the heads of men, where they are, for a 
short time, very unpleasant and unwelcome guests. 
This fly measures from 6.6 to 8.8mm. The thorax is 
very dark-brown with conspicuous yellowish markings; the 
legs are yellowish with brown rings; the abdomen is grayish- 
brown. The illustration (fig. 123) shows the structure of 
this peculiar parasite; it was made from a rather poor 
specimen. 
The whitish larva, when leaving the mother, is already 
enclosed in a very thin shell, which turns brown in about 
four hours, and bright black in twenty. The adult fly leaves 
this puparium in about four weeks. 
