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This is a member of Scathophagidae, and it recalls Cleigastra apicalis (compare http://www.dipter...d_id=20927). Usually there is a dark spot on the outside of the fore femora, but it may lack, as in this case. The species occurs in reed swamps. So is your forest in the vicinity of such? As I am not familiar with the species, an expert opinion would be helpful.
Regards, Sundew