Parasitic Flies - Tachinidae

Tachinidae flies are a large family, with hundreds of species in France. They range in size from about 2 mm up to about 20 mm. Most of them are very bristly and many resemble blowflies (Calliphoridae). They are generally parasites of caterpillars and other pre-adult insect forms (occasionally adult bugs and grasshoppers). The female Tachinid lays her eggs either directly on a caterpillar or on a plant where the egg will be ingested by the caterpillar. The egg hatches into a larva inside the caterpillar and this larva consumes the caterpillar from the inside before pupating and emerging as an adult fly.

They can be distinguished by their subscutellum, a cushion like body part which sits below the scutellum (the crescent shaped part that sits between the thorax and the abdomen on a fly). Only one other fly family has a post-scutellum. They also have a very sharp bend in the main long vein on their wing. Chris Raper has posted a photo of a typical Tachinid wing and subscutellums on his excellent blog / website, the Tachinid Recording Scheme.

Chris is extremely approachable, so if you would like a fly you suspect to be a Tachinid identified, do not hesitate to contact him. The other highly recommended site for getting flies identified from photos is the DipteraInfo forum, where there are a number of Tachinid experts happy to help. Remember that identification to species level usually depends on having several photos taken from different angles, in focus and showing a high level of detail (down to the exact position of each hair being visible, for example).

Further information on our daily blog, Days on the Claise:
Gymnosoma sp (includes photos of the lookalike species, Ectophasia crassipennis).
Tachina sp

Photographed by Loire Valley Nature:
Photographs numbered from left to right and top to bottom. 1 - 2 Tachina cf magnicornis in the Parc de Boussay, April.