96 



MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



GASTEROPHILUS INTESTINALIS (Degeer) 



The Common Horse Bot ; the Nit Fly 

 (Fig. 45) 



Synonym. — Gasterophilus equi (Clark). 



Recognition Characters. — Adult; This is a brownish-yellow fly; the thorax 

 is somewhat darker than the head and abdomen ; the latter may be marked with 

 rather indefinite blackish spots and bands. The wings are marked with a 

 grayish cross band at the middle and two spots at the apex. The hair of the 

 abdomen is short and not very conspicuous. Lenth 12-17 mm. Larva : The 

 newly emerged larva (fig. 43, B) is straplike and fusiform, tapering to both 

 extremities; it is about 0.87 mm. in length, but may attain a length of 2. mm. 

 or more before the completion of the stage. The color is translucent white. 

 The posterior spiracles are borne at the end of prominent fleshy processes. The 





Figure 45. — Gasterophilus intestinalis, adult female 



of side view. 



A, Dorsal view ; B, sketch 



second segment ventrally bears a number of spines, which are, however, no 

 longer than some of the spines on the anterior margins of other segments. The 

 third-stage larva (fig. 44, B) may be recognized by the characters given in the 

 key. 



Geographical Distribution. — Nearctic Region : New Brunswick, Quebec, 

 Ontario, Manitoba, Saskatchewan, Alberta, British Columbia, Maine, New 

 Hampshire, Vermont, Massachusetts, Connecticut, New York, New Jersey, Mary- 

 land, Virginia, North Carolina, Mississippi, Ohio, Michigan, Illinois, Minnesota, 

 Wisconsin, Iowa, Missouri, North Dakota, South Dakota, Nebraska, Kansas, Okla- 

 homa, Texas, Montana, Idaho, Wyoming, Colorado, Utah, New Mexico, Arizona, 

 Washington, Oregon, California. Neotropical Region : Jamaica, Venezuela, Brazil, 

 Chile, Argentina. Palaearctic Region : Scotland, England, Spain, France, Nether- 



