These insects, sometimes called attic flies, become pests in homes. They usually appear in late fall or early winter and again on warm, sunny days in early spring. They buzz around the home and gather in large numbers on windows, often in rooms that are not regularly used.
The cluster fly is a little larger than the common housefly and moves sluggishly. It can be recognised by the short, golden coloured hairs on its thorax, this is the part of the body to which the legs and wings are attached. The larvae, or maggots, of cluster flies develop as parasites in the bodies of earthworms. The adult flies emerge in late summer and early autumn and seek protected places to spend the winter. In many cases, this is within the walls, attics and basements of homes. Insect screens on windows offer no protection from the flies because they crawl in the home through small openings in the walls of the building. These same overwintering flies get into rooms during the winter and spring months entering through windows, around the skirting boards and through other small openings in walls and under roof tiles.