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



Figure 73. — Peronia rostrata, 

 posterior spiracles of pupa. 



Pathogenesis. — Prob- 

 ably of no medical im- 

 portance. It is known 

 to be a tertiary sheep 

 maggot, but it does not 

 invade healthy tissue. 



Figure 74. — Stomoxys calcitrans, head of 

 female, side view. 



The Genus STOMOXYS Geoffroy 



The genus is treated here in its more restricted sense ; some authors, 

 such as Patton and Zumpt, extend it to include the horn flies and their 

 relatives. 



Stomoxys is easily distinguished from other Muscidae by the fol- 

 lowing combination of characters : The proboscis is long and slender, 

 broader at its base and narrowing toward the apex ; it is horny, shin- 

 ing, and rigid, with small, inconspicuous labella, and is fitted for pierc- 

 ing and sucking blood (fig. 74) . The palpi do not extend beyond the 



middle of the haustellum. The 

 antennal arista is pectinate, with 

 no rays below. 



The genus includes a number 

 of species of grayish flies of me- 

 dium size that resemble the 

 housefly in appearance. S. calci- 

 trans (L.) is almost cosmopolitan 

 and is the only species occurring 

 in the New World, Australia, and 

 much of the Palaearctic Region. 

 Life Histories. — The females are oviparous. The larvae shun light, 

 which is detrimental to them. They breed in the excrement of many 

 animals, horse manure being favored ; they have also been reported as 

 breeding in birds' nests and in decaying vegetable matter. The adults, 

 both males and females, are savage Biters, but attack horses and other 

 domestic animals in preference to man. 



Larvae. — The first-stage maggot is whitish, translucent, and about 

 2 mm. long. The mature larva is of the ordinary muscoid type, with 

 the posterior end distinctly broader than the anterior; the posterior 

 spiracles (fig. 75) are rather small and widely separated, with three 

 strongly sinuous openings ; the rather poorly defined button is in the 

 middle. 



Figure 75. — Stomoxys calcitrans, pos- 

 terior spiracles of pupa. 



