Cluster Fly

(Pollenia spp.)

Photo by

Overview

Biology

Lifecycle: Cluster flies go through a complete metamorphosis, including egg, larval, pupal, and adult stages. The larvae of cluster flies are parasitoids that develop inside earthworms. Female cluster flies lay eggs near earthworm burrows, and the fly larvae infest and feed on the earthworms.
Overwintering Behavior: Cluster flies have a unique behavior of seeking shelter in buildings to overwinter. They often gather in large numbers in attics, wall voids, and other concealed spaces to stay warm during the colder months.
Feeding: Adult cluster flies primarily feed on flower nectar and other sugary substances, making them less of a household pest in terms of contaminating food

Food

While cluster flies feed on flower nectar, their primary focus is on overwintering and shelter rather than actively foraging for food within homes or buildings.
They do not cause the same level of concern as house flies in terms of contaminating food sources.

Cluster flies are a type of fly that are known for seeking shelter inside homes and other buildings, especially during the cooler months. They are part of the blowfly family and are different from common house flies in their behavior and habitat preferences.

Description

Size: Cluster flies are about the same size as house flies, typically measuring 6-10 millimeters in length.
Appearance: These flies have a dark gray to black thorax with golden hairs, giving them a somewhat bristly appearance. They have a distinctive, slightly sluggish flight compared to common house flies.

Habitat

Cluster flies can be found in a variety of environments, but their overwintering behavior leads them to seek refuge in human-made structures during the winter months.
They are often associated with rural and suburban areas due to their reliance on earthworms as a host for their larvae.

Articles