868 AN INTRODUCTION TO ENTOMOLOGY 



The larvae complete their growth in the lumbar region, causing as 

 they increase in size the formation of the warbles. The hole through 

 the skin into the cavity of the warble serves as a breathing hole for 

 the larva and as a means of escape when it is full-grown. The mature 

 larvae leave the warbles and drop to the ground to transform. This 

 takes place during the first half of the year. The average pupal 

 period is about one month. The adults live only a short time as 

 they are unable to feed. 



The above account refers to both of our species of warble-flies; 

 the following details chiefly compiled from Hadwen ('19) will serve 

 to distinguish the two. 



The bomb-fly, Hypoderma bovis. — The adult fly measures 14 mm. 

 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-^^ellow. 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 blunder- 

 ingly. The presence of one of these flies in a herd of cattle causes 

 them to scatter and stampede just as a crowd of people would do if 

 a bomb were thrown in their midst. For this reason Mr. R. C. Shan- 

 non ('22) has suggested "bomb-fly" as a common name for this 

 species. The name "European warble-fly" that is often applied to 

 it is not distinctive, as both of our species are of European origin. 

 The eggs are laid mostly on the outside of the hind quarters and on 

 the legs above the fetlocks; they are laid during June and July. In 

 the larva the segment in front of the spiracular segment is unarmed. 



The heel-fly, Hypoderma linedtum. — The adult fly is 12.7 mm. in 

 length ; the anterior part of the thorax is black and shining ; the alulee 

 are uniformly white; and the tail end of the abdomen is reddish- 

 orange. The eggs are laid mostly when the animals are recumbent 

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

 ground. Even when the animals are standing the fly is able to lay 

 eggs on those hairs which are close to the ground, namely on the 

 heels. The frequency with which this species lays its eggs in this 

 place has caused it to be known as the heel-fly. This species irritates 

 the cattle much less than does Hypoderma bovis, and consequently 

 is able to lay several eggs on a single hair. The eggs are usually laid 

 during May. In the larva the segment in front of the spiracular seg- 

 ment is spinose. 



Family PHASIID^ 



The Phasiids 



This is a comparatively small family, which is composed of certain 

 genera that were formerly included in the Tachinidas but which are 

 now regarded as representatives of a distinct branch of the Muscoidea. 



In this family the clypeus is more or less produced below the 

 vibrissal angles, like the bridge of a nose. The conjunctivas of the 



