Nearly identical in size and appearance to the common housefly, they feed around the eyes and mouths of large livestock. Eggs are laid only in fresh, undisturbed manure. These are a little larger than houseflies and have small, golden hairs on their thorax, or middle section. The larva parasitize the worm. When leaves begin to turn, all of these species are attracted by the warmth radiating from house walls.
Large numbers aggregate most noticeably on the south walls of isolated, white-painted farm houses.
As days shorten and temperatures fall in the autumn, they enter through small cracks in siding and around windows and doors. Many winter in the structure, while others get into living spaces. While seeking a dark hibernating crevice, they will fly around and, attracted by light, will often congregate on the insides of windows. Some years, dead flies can accumulate in a pile as high as the sill of an attic window. The occasional dusty-looking fly will emerge during the winter, to buzz around groggily, bumping into things.