The female lays eggs often in “puddled” areas near earthworm burrows. When winter approaches cluster flies seek shelter, usually September/October often in attics roof voids returning annually unless controlled.
South facing buildings are often fond to be a favourite (early spring activity may occur) Cluster flies usually gain access into a property via louvered window installation.
The cluster fly is very difficult to eliminate as they get into wall cavities. However we have seen great results from the application of residual insecticides, smoke bombs or foggers often repeated in early spring.