Flies cluster on the warm sides of buildings in late summer during the day. As the sun goes down and temperatures cool, flies crawl into the building through cracks, especially under eaves, gaps in siding, etc. They are attracted to light, light-colored siding and structures on lawns and pastures inhabited by earthworms. They become active whenever temperatures rise above 54 degrees F indoors from early autumn to mid-spring, especially around windows with sunlight. Just as they become a nuisance in the fall while seeking hibernating quarters, they are also bothersome in the spring, trying to escape.
Face flies are serious pests of cattle and horses.
They often overwinter in homes and other structures near pastures where these animals are kept. During the summer, adults annoy the faces of cattle and horses, where they lap exudation from the eyes, nostrils and mouth. The larval stage lasts three to ten days, while the entire life cycle requires 14 to 18 days. Control Measures Prevention Initiate control tactics before flies enter buildings in large numbers. Control cannot be permanent until the openings through which these flies enter the home are closed.