Musca autumnalis

This is a relative of the common housefly, which it closely resembles, and indeed the two are difficult to distinguish. The eggs are laid in fresh cow pats in the fields and the larvae feed on the dung. The adult flies live around the cattle and are not seen indoors during the summer. In the autumn they sometimes enter outhouses and cool lofts where, like cluster flies, they hide away in cracks and crevices and re- main inactive throughout the winter. In spring they become active again and move out into the open, but they may wake up in winter if there is a warm spell.

Indeed, it is not uncommon to see flies indoors during the winter. Sometimes these may belong to the two species just described, but in many cases they will just be common houseflies (p. 77). In northern Europe these do not overwinter in any particular stage. Many spend the winter in warm farm buildings, where they may breed throughout the year, and may therefore appear in the house even in the middle of winter.