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Many thanks Sundew. The link you gave does seem to show the very same thing: Scathophaga stercoraria infected with Entomopthora muscae, and that fly also ended up with its wings spread open. I'd come across photos of other infected S.s in this pose so was fairly sure I'd got it right. Maybe this posture (high up on an exposed plant) helps ensure dispersal of the fungal spores. Insect fungi can be very controlling for sure: I've come across ants in the tropics clamped to vegetation with their jaws in exposed positions a few feet off the ground, with macabre fruiting bodies sprouting from their heads, and it seems this kind of relationship had evolved by around 50m years ago http://www.guardian.co.uk/science/2010/aug/18/zombie-carpenter-ant-fungus . Nature can be nasty!