These are dark greyish flies about 8mm
long with yellowish hairs on the back and
with overlapping wings. In autumn they congregate
in large numbers in upper rooms or roof
spaces of houses to hibernate. A mass of
cluster flies has a characteristic smell.
They are sluggish in flight and are a nuisance
in the house. The larvae of one species
are parasitic upon certain earthworms, so
this species is more common in rural areas.
