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I found a very nice fly last week. It acted like a Bombyliid fly, like a Villa sp and I was convinced that it was one, until I looked at the specimen under the microscope. The wing venation did not suit Bombyliidae, it was obviously a Calyptrate fly. I first thought it was a Tachinid, around Tachina, but I could not find anything similar in Tachinidae. Than I remembered that this could be a fly within Oestridae sensu lato. (Nowadays it seem that this family is split into several more families.) After this the fly was easy keyed as Hypoderma diana.

Any other thoughts?

This is a new family for me and for the gallery here, where you can find another view of this fly.

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it seems really an oestrid fly (Family Oestridae)! I wish to see them... :)
I suppose that they are near from horses. ;)

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Well this one is near deer and roe deer, but there are several species, each with a different host preference.

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YES, Gabor! In Pjotr it says that the larvae can be in "sheep and goats.. (...) but also occasionally antelopes, deer, camels, and horses." :)

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I made the photos in a forest clearing quite far away from any animal husbandry, so I really assume that the natural host is the roe deer. This species is known to spend its larval stages in Cervidae, mostly in the nose epithelium and later under the skin (hence the name for the subfamily-family Hypodermatidae).

The adult stage of these species lasts only for a few days, therefore one must be quite lucky to find them. When I made these photos I had the feeling that the flies had formed a lek, a territory for choosing a mate.

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yes. I read that it is not easy to spot oestrid flies due that fact you appointed - small adult stage. They also seem to be very inactive.

Are you talking about hilltopping? ;)