Name: St Mark's Fly
Scientific name: Bibio marci
Nature Stars: 40
About: A very common, long, shiny black fly which can be found in large numbers during the spring around woodland edges, fields and wetlands. Hangs in the air over the vegetation, drifting along with their legs dangling in the air. St Marks Flies will often land on any objects in their way, including fence posts and people. Males and females look very different: the male has very large eyes, while the female has a tiny head with even tinier eyes. The larvae live in the soil feeding on rotting vegetation.
How to identify: There are several species of closely related Bibio flies that can be very difficult to tell apart. In the late summer the Heather Fly (Bibio pomonae) hatches in large number on moorlands: it looks very similar to St Mark's Fly, but the base of its legs is orangey-red. Another species is Bibio hortulanus, common in gardens in Spring: in this species, the female is not black but a rich brick red.
Fantastic fact: The name comes from the fact that this species is often on the wing in large numbers around April 25th, St Mark's Day.
Photograph credit: Photo credit tbc