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 verj^ 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, ver\^ unpleasant and unwelcome guests. 



This fly measures from 6.G 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. 



