The Cluster Fly, Pollenia rudis (Diptera: Calliphoridae)

Cluster flies (Pollenia rudis (Fabricius) ) become a serious problem and a major pest in rural homes, churches, and other structures in the autumn when they enter buildings to hibernate, and again in the spring when they seek ways to escape to the outside. Heavily infested buildings may contain several thousands of these flies. Sometimes a few thousand of them aggregate and form a “cluster,” whence their popular name. While they are not filth flies, they are severe nuisances when they gain entrance and fly in huge numbers about living quarters.