DIPTERA 321 



(Fig. 564). The eggs are laid mostly when the cattle are recumbent and 

 on all parts which the fly can reach when it is resting on the ground. 



Fig. 564. — Hypoderma lineatum. 



Even when the cows are standing the fly is able to lay eggs on those hairs 

 which are close to the ground, namely on the heels. 



The eggs hatch and the larvae penetrate the skin at once and burrow 

 their way, probably under the hide, to the neck. Here they enter the 

 walls of the oesophagus and work down its tissues to the diaphragm 

 and thence up the ribs to their resting places along each side of the back- 

 bone beneath the skin. Here each one forms a swelling or " warble." 

 In the spring, each maggot works out through the hole in the hide, drops 

 to the ground, pupates and in about 40 days emerges as a fly. This fly 

 is especially troublesome to milch cows. 



The bomb-fly, Hypoderma bovis. — The adult fly measures a little 

 over \ an inch in length; there is yellow hair on the anterior part of 

 the thorax; the alulae are bordered with reddish-brown; and the tail end 

 of the abdomen is orange-yellow. As a rule the flies lay their eggs while 

 the cattle are running; the eggs are laid singly at the roots of the hairs; 

 the flies are clumsy insects and strike at the animals blunderingly. The 

 presence of one of these flies in a herd of cattle causes them to scatter 

 and stampede. This species is prevalent in the North and is also annoy- 

 ing to milch cows. 



Family Calliphorid^e 

 The Blow-fly Family 



Certain members of this family are very familiar objects and are 

 commonly known as blow-flies, bluebottle-flies, or greenbottle-flies. With 

 these, and with most other members of the family as well, the body, 

 especially the abdomen, is metallic-blue or green in color. 



The larvae of the different species vary in habits; some have been 

 bred from cow-dung; some feed on fresh or decaying meat and on the 

 bodies of dead animals; one frequently infests wounds on animals, and 



