THE FLIES THAT CAUSE MYIASIS IN MAX 



93 



are small, with a bare arista. The mouth parts are greatly reduced 

 and nonfunctional, the fly taking no food as an adult. TTie thorax 

 is hairy but without well-developed bristles: the wing (fig. 42) has an 

 easily recognizable venation, with the subcosta and the branches of 

 the radius running close to the costal margin, vein ?n 1+2 running 

 straight toward the posterior margin or slightly bowed downward 

 but never with an upcurved bend, and vein 1st A reaching the wing 

 margin. The membrane of the wing is crinkly and the microtrichia 

 scarcely evident. The abdomen is elongated-oval, with the apex 

 curved'under : in some species the ovipositor is long and strongly re- 

 curved beneath the abdomen. The adults in size and appearance bear 

 a strong resemblance to the honeybee, and this resemblance is ac- 

 centuated by the bee-like buzzing produced by their flight. 



Life Histories. — The normal hosts are horses and other Equidae. 

 The adult is short-lived and takes no food. The female usually deposits 



Figure ■!-■ — GasterophUus haemorrhoidalis, wing. 



eggs singly while in flight upon hairs on the body of the animal, the 

 part of the body chosen being characteristic of the species of fly. The 

 number of eggs produced by each female differs and is correlated 

 somewhat with the chances of survival of the progeny. The first- 

 stage larva, after hatching, makes its way to the mouth of the horse 

 and buries itself in a pocket or tunnel which it forms in the epithelial 

 tissue of the mouth or tongue. Details of the life histories vary with 

 the species, but the parasite always completes its larval development 

 in the stomach or intestine, is passed with the feces, and enters the 

 ground to pupate. The period spent in the digestive tract of the 

 horse ranges from 8 to 11 months. 



Man is an accidental host, and in him the larva is almost always in- 

 capable of developing beyond the first stage. He may become in- 

 ferred, while around horses, by the fly mistaking him as a suitable host 

 for her progeny, or by his rubbing r petting an animal upon which 

 the fly has oviposited. In man the larva, not finding the proper place 

 in which to burrow and molt, enters the skin and wanders about in 

 search of such a place, thus producing the characteristic symptoms of 

 creeping eruption. 



Larva. — The first-stage larva (fig. 43) is elongated and fusiform, 

 broadest in front of the middle: it is composed of 13 segments, the 

 first or head segment being short and the thirteenth bearing the 



