310 NORTH AMERICAN DIPTERA 



Family Piophilidae 



Piophila casei. 



The flies included in this family rarely exceed five millimeters in 

 length, and are usually glistening black or slightly bluish metallic in 

 lustre. 



Face not carinate, occiput more or less flattened; always two pairs 

 of vertical bristles; postvertical bristles divergent; fronto-orbital bris- 

 tles varying from two pairs to none; antennae decumbent, the third 

 segment elongate oval, arista bare in the American species; cheeks 

 rarely fringed with hairs, the oral vibrissa? usually prominent, para- 

 facials not differentiated as a linear orbital boundary; palpi well de- 

 veloped. i\Iesonotum almost always finely pubescent and ]iolished; 

 stcrnopleura never pruinose; one pair of dorsocentral bristles, four 

 scutellar bristles. Legs of the male never toothed or deformed, the front 

 femora usually furnished with long but delicate bristles. Abdomen 

 more or less polished, ])ubescent but without bristles, broad, depressed, 

 not constricted at the base; genitalia of the male more or less hidden 

 asymmetrical; ovipositor extensile. Auxiliary vein terminating close 

 to the end of the first vein, the costa broken at or near the termination, 

 third and fourth veins parallel or more or less diverging, anal vein 

 usually curved and evanescent apically, discal cell usually large, with 

 the posterior crossvein usually long. 



The larvffi are, in general, scavengers but some of them live in 

 cheese and preserved meats. Piophila casei, the cheese-skipper, has a 

 rather conical larva, pointed anteriorly and truncate posteriorly; body 

 shining and smooth; antennae two segmented; mouth hooks separated 

 and divergent; anterior spiracles whitish, the abdominal travelling 



