Tiger Fly Coenosia tigrina
In Britain some 20 species of Coenosia may be found. Most seen is this Tiger Fly. It may be identified relatively easily, which is a miracle in the world of the flies. The body is greyish, often light-grey. Both thorax and abdomen are punctuated. The dots are black, but may vary in size. The legs are grey as well, with some reddish-brown patches, especially near the joints. On the tibia are some long hairs near the joints. But at 3/4 of the tibia there will be one or more extra hairs. On the tibia of the middle leg for instance are 2 extra hairs at about 3/4 from the top. The tibia is the longest part of the leg.
The larvae are parasites to earth worms, which are eaten from within. It takes the larvae 2 to 4 weeks to eat their host. Next the pupate in the earth. When the pupa doesn't overwinter, the new fly appears after 2 to 4 weeks. The adults are formidable hunters, even catching prey larger than they are themselves. They mainly hunt for flies (including other Coenosia), but grasshoppers are also regularly taken.
The common name Tiger Fly is a bit confusing, for it is also used for the genus Coenosia. Thus the Tiger Fly on this page could better be named the Common Tiger Fly.