Wed, 06 May 2026 23:52:47 +0000

They’re Creeping In Unnoticed—Here’s What Cluster Flies Are Really Doing You may not have noticed, but cluster flies are quietly making their presence known—and they’re far more than just unwelcome guests. These sleek, grayish-black flies often go unnoticed until they gather in swarms around windows, doors, and light sources during late summer and fall. While their sudden appearance might seem like a seasonal nuisance, understanding what cluster flies are really doing can help you take effective action to keep them out. Who Are Cluster Flies? Cluster flies, scientifically known as Pollenia rudiceps, are one of the most common parasitic flies in the U.S. Unlike blowflies or house flies, cluster flies don’t breed in decaying matter or contamination. Instead, they parasitize earthworms in the soil, laying eggs near compromises in your home’s foundation. Their larvae consume earthworms from the inside, weakening garden ecosystems—and your house’s defenses.