234 



NORTH AMERICAN DIPTERA 



Family Phoridse 



Megaselia species. 



Small or minute flies, often wingless, usually with a hunch-backed 

 appearance. 



Head small, ratlier flattened; front wide, usually bristled; face 

 short and concave; oral opening large, the proboscis usually fleshy; 

 palpi large, usually bristled; eyes never large, the ocelli sometimes 

 absent in the apterous forms. Antenna with three segments, the third 

 large, the basal two small; arista dorsal or apical. Thorax usually 

 arched, the scutellum absent in some wingless forms. Abdomen short, 

 iLsually tapering posteriorly, sometimes partly membranous, especially 

 in the wingless forms; male genitalia often large, in the female small 

 and projecting, large and adapted for piercing in some genera. Legs 

 short, well developed, the tibae with or without l)ristles; posterior femora 

 usually more or less laterally compressed. Wings large, ])oorly de- 

 veloped or absent, the fully developed wings with two strong longitudi- 

 nal veins and four or five fine ones. 



The adults are readily recognized by their characteristic antennee 

 and wing venation. They are found almost everywhere but are par- 

 ticularly aliundant about decaying vegetation, on leaves and windows or 

 in the nests of termites and ants, and following armies of ants. The 

 alate adults move about on leaves with a quick, jerky movement which 

 is quite characteristic of the family. 



