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1. I will address it later.
2a. Males (the image is of a male) and female can both be apterous.
2b. Pitkin, B.R., 1988. Lesser dung flies. Diptera: Sphaeroceridae. - Handbooks for the Identification of British Insects 10(5e): 1-175. That is the only accessible key I know to species level for Europe.