Cluster fly

Definition

A member of the dipteran genus Pollenia (family Polleniidae), recognized for its habit of aggregating in large numbers inside buildings during autumn and winter. Unlike blow flies (Calliphoridae), cluster flies do not breed in carrion or human food; instead, females deposit eggs near earthworm burrows, and the larvae parasitize lumbricid earthworms. Adults are sluggish, bristly, and slightly larger than house flies, with a golden sheen on the thorax caused by yellowish hairs.

Etymology

From the autumn/winter aggregating behavior in attics and wall voids; the scientific name Pollenia derives from Latin pollen, 'fine flour or dust,' referring to the dusty appearance of the thorax.

Example

Homeowners often mistake autumn swarms of Pollenia rudis in unused chimneys for a sign of indoor breeding, when the flies are actually seeking overwintering shelter after completing larval development in nearby soil.

Synonyms

• attic fly
• Pollenia

Related Terms

• blow fly
• earthworm parasite
• overwintering behavior
• Polleniidae
• synanthropic insect

Usage Notes

Strictly refers to Pollenia species, not to any fly found in clusters; distinguished from blow flies by the parasitic life cycle and non-pest status regarding food contamination. The common name is most frequently applied to Pollenia rudis in North America and Europe.