Scathophaga Meigen, 1803

Many species of Scathophaga vary greatly in size, and smaller individuals sometimes lack typical colouring and chaetotaxy. For example, small males may resemble females in general appearance and colouring. This appears to be related to their biology. The larval pabulorum is often in discrete patches (such as a cow-pat or a pile of rotting vegetable matter) in which potentially large numbers of larvae are confined, but which offers a finite amount of food. If more larvae are present than the food is sufficient to support, then intense competition occurs and they are forced to pupate prematurely. For example, Larsen (1943)[1] found that even at four days old, S. stercoraria larvae could pupate, but most did not emerge successfully. Many such pupae fail to survive, but those that do hatch into small and atypical adults (at least in Scathophaga stercoraria where this phenomenon has been most studied) which are often sterile and have sometimes been referred to as a separate species, S. merdaria (F.), or as variety (Gibbons, 1980[2]). The practical consequence is that it is not always possible to reliably determine isolated individuals. Adults are often encountered in considerable abundance in the field, so it is worth retaining a number of specimens covering the full range of size and general appearance. The features of the male genitalia that are readily visible externally do not seem to be all that useful in this genus. With the exception of S. scybalaria, most species have simple, stout, black, slightly hooked claspers.

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