DIPTERA . 
465 
earth, fungi, and decaying wood. They feed on decaying 
animal and vegetable matter and are said to be predaceous 
also. The pupae are free. 
Fig. 565.—Wing of Thereva. 
The family is a comparatively small one, including but 
few genera and species. 
Family SCFNOPINID^: (Scen-o-pin'i-dae). 
The Window-flies . 
The window-flies are so-called because the best-known 
species are found almost exclusively on windows ; but the 
conclusion that these are the most common flies found on 
windows should not be drawn from this name; for such is 
not the case. 
These flies are of medium size, our most common species 
measuring one-fourth inch in length. They are usually 
black, and are not clothed with bristles. 
The thorax is prominent, and the abdomen 
is flattened and somewhat bent down, so 
that the body when viewed from the side 
presents a humpbacked appearance (Fig. F , o ^ 
566). When at rest, the wings lie parallel, Scenopinus. 
one over the other, on the abdomen ; when in this position 
they are very inconspicuous. There are three ocelli. The 
antennae are three-jointed ; the first and second segments 
are short, the third is long and bears neither a style nor a 
bristle (Fig. 567). 
31 
