Although these flies do not pose a health risk, they can be extremely annoying!!
The telltale signs are finding dead flies on the window sills and appearance of flies when going into the loft.
As the name suggests, cluster flies gather together in a cluster to survive the winter, window frames and loft spaces offer the perfect habitat for them. In the spring they vacate and lay their larvae in leaf matter/mulch, these larvae are parasitic and seek out earthworms.
After they are fully matured, they pupate in the earth and then hatch out into the flies, during the remainder of the summer these flies survive on nectar.
Only when autumn arrives do they start to become a nuisance again as they try to find a suitable place to gather for the winter.