Parasitic Flies - Tachinidae

To identify flies to family level use a simple wing venation key such as A Key to the Families of British Diptera, an AIDGAP by D. Unwin, published by the FSC and available as a free download (scroll down to the titles list) or a more detailed key which includes many physical characters such as The European Families of the Diptera by P. Oosterbroek. The expert dipterists on the DipteraInfo forum are also very happy to identify, often to species level, from good photographs.

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.

Cylindromyia bicolor -- the easiest of this distinctive genus to identify as it is the only species with a red tipped abdomen. It is also rather large for the genus and very obvious in the field. Seen here nectaring on Wild Carrot Daucus carota.

Cylindromyia bicolor -- the easiest of this distinctive genus to identify as it is the only species with a red tipped abdomen. It is also rather large for the genus and very obvious in the field. Seen here nectaring on Wild Carrot Daucus carota.

Giant Tachinid Fly Tachina grossa, a distinctive and easy to identify species. It is large (15 - 20 mm), with a black body covered in bristles, a yellow head and a very sharp bend in the main vein on the wing.

Giant Tachinid Fly Tachina grossa. Don't confuse with unrelated lookalike Noon Fly Mesembrina meridiana (Muscidae), which also has a black body, yellow wing bases and a yellow face. The difference is that the Noon Fly is black on top of the head and a curve rather than a right angle bend on the main wing vein.

Giant Tachinid Fly Tachina grossa can be found in heathland and parasitises the caterpillars of moths such as the Oak Eggar Lasiocampa quercus.

Pales pavida, at first glance looks like a small dull bluebottle Calliphora sp. The main give away is the red-brown tip to the scutellum (the small semi-circular part between the thorax and the abdomen), which bluebottles do not have. Its larvae are endoparasitoids of the caterpillars of many species of moths and butterflies, including some significant pest species.

Peleteria cf varia, nectaring on flowering Ivy Hedera helix. Peleteria are medium large flies, closely related to Tachina. They can be identified by the 2-4 black bristles between the eye and the mouth, known as 'the Peleteria bristles', just visible in this photo (don't confuse with the strong black vibrissae bristles, which are closer to the mouth). This species has orangey-yellow second antennal segments and is the most common of the Peleteria here. Found in warm, open, dry habitats, June to September (November). The larval host is unknown.

Peleteria cf varia, the same individual as above, demonstrating how the colour can appear completely different from a different angle. This is due to the pruinose scales (also known as 'dusting') which this species has to a greater or lesser extent (rather variable from individual to individual and depending on the age of the specimen, as the dusting can wear off).

Male Ectophasia crassipennis on Wild Carrot Daucus carota. This species is common in late summer. It is very variable in appearance (colour of body, dark marks on wings, size). The abdomen is noticeably flattened. It parasitizes bugs such as stink bugs, shield bugs and leaf-footed bugs.