Cluster Fly vs Thick-headed Fly

Side-by-side species comparison

Attribute Cluster Fly Thick-headed Fly
Scientific Name Pollenia rudis Physocephala rufipes
Order Diptera Diptera
Family Calliphoridae Conopidae
Size 8-10 mm 8-14 mm
Habitat Gardens Underground
Diet Parasites Parasitoids
Regions Europe, North America Europe
Conservation Least Concern Least Concern

Cluster Fly

A medium-sized, dark gray fly with golden-brown hairs on the thorax. In autumn, it gathers in large clusters inside buildings to hibernate, sometimes in the thousands.

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Did You Know?

The larvae of this fly are earthworm parasites, burrowing into the worm through its skin and consuming it alive from the inside over several weeks.

Thick-headed Fly

A wasp-mimicking fly that parasitizes bumblebees by injecting eggs into them mid-flight.

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Did You Know?

Infected bumblebees bury themselves in soil where the fly larva pupates.