Greenish Flies Entering Siding Holes: Solitary Bees, Not Pests

Central Wisconsin homeowner sees greenish flies entering holes in siding grooves, with greenish material at holes. Woodpecker damage noted.

Identification: Solitary Bees

These are solitary bees (likely mason bees or leafcutter bees), not flies. They nest in pre-existing holes in wood or siding.

Key Facts

• Beneficial pollinators—do not sting aggressively
• Not structural pests—use existing holes, don't drill new ones
• Green material = pollen/nectar provisions for larvae
• Woodpeckers eat bee larvae (secondary damage)

Management

Caulk and paint holes after bees emerge (late spring). No insecticide needed. These bees are valuable pollinators.