THE FLIES THAT CAUSE MYIASIS IN MAN 135 



by denticles, and the posterior end is papillated. The second larval 

 stage is similar to the first, except for the usual changes in the posterior 

 spiracles and the development of anterior ones. The third-stage larva 

 has characteristic posterior spiracles (fig. 77) ; the peritreme is very 

 thick and the three slits are arcuate; beside the slits, there are four 

 feebly sclerotized areas, each bordered outwardly by a fanlike fringe 

 of hairs; each anterior spiracle ends in four to six fingerlike processes. 

 Pathogenesis. — Most species of Muscina are saprophytic, at least 

 in the earlier stages. The only species known to be involved in the 

 production of myiasis in man is M. stdbvlans; in man, it has been 

 recorded only as an intestinal parasite, although it has been known 

 to produce wound myiasis in animals. 



KEY TO SPECIES 



The following key will separate the four most common Muscina species of the 

 Holarctic Region. The other species of this region and the rest of the world are 

 either of doubtful validity or of uncommon occurrence. 



ADULTS 



1. Tibiae yellow stabulans (Fallen) 



Legs entirely black 2 



2. Palpi black; vein nh +2 . but slightly curved upward (cf. stabulans, fig. 



78, A) assimilis (Fallen) 



Figure 78. — Venation of apical half of wing: .4, Muscina stabulans; B, M. 



pascuorum 



Palpi yellow; vein nii +2 strongly curved upward (fig. 78, B) 3 



3. Abdomen without a trace of red laterally; grayish pollen abundant, 



especially on the thorax pabulorum (Fallen) 



Abdomen usually brownish red at the base laterally ; body with bluish 



reflections and without abundant grayish pollen pascuorum Linnaeus 



MUSCINA STABULANS (Fallen) 



The False Stablefly 



Recognition Characters. — Adult: The body is largely black, covered with 

 thick grayish pollen; the abdomen may be more or less reddish on the sides, or 

 may be entirely black; and the scutellum is broadly reddish at the apex. The 

 first two segments of the antennae and the base of the third are largely red. 

 The palpi, tibiae, and about the apical half of the femora are yellow. Vein r»i+j 



