Name: Cluster Flies – Pollenia rudis

Lifecycle: Complete metamorphosis

Egg: Laid in damp soil or rotting vegetation. Hatch within 1 week.

Larvae: Soon after they hatch they seek out earthworms to parasitise. Development time within the worm is several weeks.

Pupae: Larvae migrate out of the deceased worm host and pupate in the soil.

Adult: Adult emergence is environmentally triggered with an average of 2 generations a year in the UK, adults will also overwinter in buildings seeking cracks and crevices for shelter.

Description
The adults are 6 mm long with a black thorax covered in a sheen of golden hairs. Usually appearing in great numbers after periods of cold weather with a slow and sluggish flight.

Habitat
The larvae are parasitic and therefore difficult to monitor or control. Adults will spend the majority of the year outside and only come into close contact with humans during the late autumn when they look to overwinter.

Signs of infestation
Large numbers of adults will cluster into cracks and crevices in houses, typically most commonly found in window edging or in roof spaces.

References
The British Pest Management Manual. Section 5, pg 151.
Lab notes, Tarakan International