Cluster flies typically come from the outdoors during the fall and early winter months, seeking warmth and shelter in buildings to overwinter. They are most commonly found in attics, wall voids, and other similar spaces. They are attracted to the warmth and light of buildings, and will often congregate in large numbers in these areas. These flies typically emerge in the spring when the weather warms up and they become active again. Cluster flies are known to lay eggs in soil, and the maggots of the flies feed on earthworm. Adult flies are attracted to the sun and can be found resting on walls and windowsills of buildings on warm sunny days. They are not known to breed or feed indoors, and are considered a nuisance pest because of their presence in large numbers.