Red-thighed St Mark's Fly

Bibio pomonae can reach a length of about 10–13 millimetres (0.39–0.51 in), while the length of the wings reaches 8–12 millimetres (0.31–0.47 in). The basic body color is shiny black, with a black long abdomen, deep crimson-red femurs and dark tibiae and tarsi. Front tibia show a pair of large spurs. Wings are milky-white with darkened veins on the costal area and a dark spot on the leading edge. The 10-segmented antennae are relatively short and thick. Males and females are very different, as the holoptic males show very large eyes and a flattened abdomen, while the females have small head and eyes and a sharp abdomen. The larvae are reddish brown.

This species can be found across most of the Palearctic realm (Europe and North Asia), but in southern Europe can be found only in the mountains.