Cluster flies are a member of the blowfly family and are widely distributed throughout the United States, except for the states bordering Mexico. TThese insects enter houses in the fall to hibernate and often gather in secluded and sometimes inaccessible places, such as wall cavities, attics and false ceilings. In the spring, cluster flies become active and in attempting to leave their hibernation site, they commonly end up inside the living space of homes and buildings where they become a nuisance. In early spring, they are sluggish, but do not fly about noisily in buildings like other house-invading flies.
Cluster Fly Habitat
Cluster flies normally live outdoors where they frequent flowers and ripe fruits. With the approach of cool weather, they enter homes and buildings to overwinter. Here they hide, often in clusters, in nooks and dark corners, under clothing in closets, beneath curtains, in wall voids, and behind pictures and furniture. The increasing warmth of spring days, induces activity, and flies may emerge from hibernation, inside, rather than outside the home. Once inside, the flies crawl sluggishly over the walls, and often fall into food on the table.
Cluster Fly Behavior – Threats – Dangers
Unlike typical blowflies, cluster flies are not believed to be a health hazard because they are not attracted to human foods. However, their presence can be annoying, as they tend to travel in huge swarms of thousands of flies. In the fall, as adult flies seek shelter to spend the winter months, they gather near windows in buildings and homes, spinning around and buzzing noisily. When swatted, they tend to leave a greasy spot. While they hibernate over the winter, their accumulated excrement can give off a noticeable stench and they may also stain fabrics and walls.
Cluster Fly Prevention
To deter a cluster fly infestation, the best action you can take, is to keep them from coming indoors. Seal cracks, windows and doors, and repair damaged screens. Seal around electrical outlets, switch boxes and vents, especially on the south side of buildings, where cluster flies most commonly enter. You can also use a vacuum cleaner to remove dead, dying or sluggish flies.