PEST NAME :  CLUSTER FLY (Pollenia rudis)

SIZE, SHAPE AND COLOUR :  6mm long. Wingspan 10mm. A largish fly with a distinctive bristly yellowish black marked abdomen. The thorax is covered with yellow-gold hairs. Large reddish compound eyes.

BIOLOGY :  Eggs laid loosely on damp soil and in leaf litter. Larvae hatch after a week and seek out earthworms. They bore through the wall of the victim’s body. After it has grown to full size it bores its way out of the worm and pupates in the soil. 

Depending on the weather 2 generations are normal but up to 4 are possible. Flies hatch from the pupae and live outdoors. They start to enter buildings in large numbers in late September onwards into November when the temperature starts to fall.

PREFERRED FOODS :  As above, the earthworm is the food source of the larvae. The adult fly feeds on nectar from flowers.  They only enter buildings in order to hibernate.

HABITAT :  South west and mainly south facing buildings are favoured. The flies will invade cladded buildings silos. Will enter roof spaces and voids via small gaps and crevices in the fabric.  They will cluster on the exterior of buildings in huge numbers prior to crawling into the harbourages.  In the spring the warmth revives them and they start to leave buildings in numbers.

For more information about different types of flies see below: