Drone Fly (Rat-tailed Maggot)

Eristalis tenax (family Syrphidae) is a 10-15 mm hover fly that closely mimics a honey bee drone, with a brown-and-orange banded abdomen, dense pile on the thorax, and large reddish compound eyes. Unlike bees it has one pair of wings, short antennae, and the characteristic syrphid false vein. Females lay eggs at the margin of foul, oxygen-poor water. Larvae are the well-known 'rat-tailed maggots': grey, sac-like larvae with a telescoping posterior breathing siphon up to three times body length, allowing them to feed in liquid organic sludge while breathing atmospheric air. Development takes roughly 3-5 weeks; adults overwinter in sheltered structures.

Adults are strong, hovering fliers and important pollinators, feeding on nectar and pollen at flowers; they are harmless and cannot sting, but their bee mimicry frequently triggers unnecessary control calls. In autumn adults enter buildings through eave gaps, attic vents, and window frames to overwinter, then become active on warm days and cluster at sunlit windows. Larvae thrive in septic-strength liquid: manure lagoons, clogged drains, sewage seepage, and stagnant tanks. Larval presence indoors is an important diagnostic clue pointing to a sanitary drain break or unsealed sewage source.