Come fall, however, and they may be taken by surprise by an equally pesky, yet mostly innocuous, household pest: cluster flies
As the days grow shorter and temperatures drop, the large, black cluster flies start entering homes in the search of protected overwintering sites, and they may be seen flying around in large numbers throughout winter and early spring. They show a landing preference for warm, sunny locations usually on the south- and west-facing walls of light colored buildings. Structures situated on open hilltops or near meadows and lawns appear more attractive due to the existence of the large populations of earthworms
, their preferred host.
They enter homes through small openings, such as gaps under eaves, as well as open windows and doors. They congregate in large numbers (thus the name 'cluster' flies) in walls, attics, and basements, waiting for spring to emerge and start a new life cycle outdoors.