During winter warm spells and in the spring, many find their way from attics or wall voids into rooms, accumulating around the windows. In their semi-dormant state, the flies are sluggish and behave erratically. They may land on a person's face and return persistently after being brushed away. Contrary to popular impression, face flies do not breed and multiply in attics and homes, nor do they feed during the winter. In spring, the face flies mate shortly after emergence from winter quarters.
Females then fly to pastures and seek horses or cattle.
They feed on exudations from eyes and nostrils, and lay their eggs in fresh cow dung. Several generations occur in pastures each summer before the flies again seek protection for the winter. Some homes are attractive to face flies and vulnerable to their entry year after year. Thus, accumulations of dead flies in unseen places eventually can be measured by the bucketful or scoop shovel. The carpet beetles lay eggs on the dead flies.