Bibio pomonae, common name red-thighed St Mark's fly or heather fly, is a species of fly (Diptera) belonging to the family Bibionidae.
Bibio pomonae can reach a length of about 10-, while the length of the wings reaches 8-.[1] 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.[2] The larvae are reddish brown.
Adults feed mostly on nectar and are important pollinators.[2] Larvae develop during Fall and Winter feeding on dead leaves, compost, decaying organic matter and Poaceae roots [1] [3]
Adults are late summer flyers, but they occur from May to October.[1] [4] In Norway's Hardangarvidda it has been observed that they appear in large numbers every third year, which suggests the larvae take three years to develop.[5]
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.[6]
This fly occurs in hedge rows of hill countries, on moorland and mountain birch forests, in woodland edges, fields and in wetlands.[1]