The Cluster Fly has a crooked checkerboard patterned black and grey body. The area behind the head is covered with golden yellow hairs. They breed outside and lay their eggs in the ground in late spring to early fall. The larvae hatch in a few days then invade a live earthworm, feeding on their host for about three weeks until they enter the pupate stage where they stay through winter and emerge in warmer weather as adults.
The adult Cluster fly will seek warmer temperatures indoors, hiding in small crevices or attic spaces, clustering inside walls warmed by the sun or near sunlit windows. It is often finding them together in the sunlight that a homeowner first discovers they are inside. They are clumsy flyers and bump into things when seeking warm and light. When knocked down they will often land on their backs and spin wildly trying to turn themselves over.
Black, grey and yellow
Ensure all windows and attic ventilations are covered with screens.
The Cluster Fly is most active in spring and summer.