Cluster flies are large slow flying insects which much of the time appears listless. They are light attractant and typically as days shorten and the weather cools, Cluster flies enter roof spaces and cladded buildings, which are surrounded by fields, although they can travel up to a mile. They usually rest in attics or between walls which are south west facing which receive the most sunlight.
Breeding: Eggs are laid loosely on damp soil and in leaf litter; larvae hatch after a week and are parasitic seeking out their hosts – earthworms. They bore through the wall of the earthworm’s body at any point. After it has grown to full size it bores its way out of the worm and pupates in the soil.