(Pollenia rudis)
Cluster Fly


Adults live harmlessly out doors during summer but may enter buildings (usually roof spaces and lofts but also through windows into rooms) in autumn to hibernate, sometimes in vast numbers. Other unrelated species may also cluster.


Egg - larva - pupa - adult. Eggs - laid in damp soil, rotting vegetation. Larvae - soon after emergence seek out and parasitise earthworms which are eventually killed. Development several weeks. Pupae - in soil. Adults - 6mm long, blackish, with fine golden hairs on thorax (sometimes rubbed off). Often two generations per year.


May be severe nuisance if large numbers of adults enter inhabited parts of buildings.Some buildings infested each autumn year after year.


Can be controlled inside buildings using a low level insecticide. (Treatment can only be applied within loft space so long as bats are not present)

Interesting facts