@Leptogaster: Apologies for this late reply, haven't been here for a while. I think the best key is still EO Engel 1930. http://books.google.nl/books/about/Die_Fliegen_der_pal%C3%A4arktischen_Region.html?id=9EkvSwAACAAJ&redir_esc=y In German........
Oops! : ) I probably was too fast then and that is a dangerous thing when identifying Machimus sp. Especially when they are from a region i'm not familiar with! On diptera.info i added a cf and a questionmark.regarding the date. Now i'm sure it isn't T atricapillus. But i know nothing of the Portuguese asilidae. Is ther a good referncework and or key to species of Portugal?. My apologies.
Hello Valter, Based on the shape of the extension of the 8th sternite this fly is not T. atricapillus because that species has a "swallowtail". This creature is probably Machimus cf lacinulatus. Kind regards, Reinoud van den Broek (Validator Asilidae Waarneming.nl, Waarnemingen.be