180 INSECTS AND MAN 



pierced the host skin with her ovipositor, and so laid her 

 eggs hypodermically. In reality, the eggs are attached to 

 the hairs of the legs, often at a point just above the hoof, 

 a fact which has earned these insects the name of " heel 

 fly" in America. This probably explains why cattle so 

 frequently stand with their legs in water during the fly 

 season, and so avoid the attentions of this baneful insect. 

 It is thought that, as in the case of horses attacked by 

 the horse bot fly, so cattle lick the eggs on their hair 

 and the larvae are carried to their mouths, where, being 

 strongly spined, they bore their way into the soft tissues 

 of the throat. Once there, they reach the second or smooth 

 stage and wander through the connective tissues of the 

 host till they arrive just below the skin of the back. At 

 this point a moult takes place; they once more become 

 spiny and bore a hole through the skin, in order to obtain 

 air, and, by so doing, absolutely ruin the hide. 1 



During the last stage the maggot lies head downwards 

 in the subcutaneous cyst, with its spiracles pointing up- 

 wards to the air, its presence made evident by the raised 

 lumps or warbles which decorate its host. This is the 

 period of growth, and the maggot waxes fat on the products 

 of inflammation which its presence causes. Lest there be 

 any diminution in the supply of nutriment, the prickles are, 

 from time to time, raised and depressed into the abscess, 

 and the irritation which this entails ensures a copious 

 supply of pus. When fully fed, the larvae are rather more 

 than an inch in length, and of a yellowish-white colour. 

 They emerge from the warbles, usually in the early morn- 

 ing, and fall to the ground, which they may or may not 

 enter. In either event, they contract and become nearly 

 black in colour as they change into puparia, whence, in 

 from three to six weeks, the flies emerge. The adults of 



1 Professor Carpenter has just announced the results of some experi- 

 ments, which show that the newly emerged larvse bore directly into the 

 host's skin. 



