Large Bee Fly

Bombylius major — the large bee fly — is one of the most extraordinary flies in temperate Europe and one of about 5,000 species in family Bombyliidae (the bee flies). Adults are 8-15 mm body length with dense brown-and-black fur covering the body, transparent wings with characteristic dark front-edge bands, and a long thin proboscis nearly as long as the body. The species is one of the most-cited examples of Batesian mimicry in flies — bee flies look so much like small bumblebees that birds, lizards, and other visual predators avoid them with the same caution they apply to actual stinging bees, even though bee flies have no sting at all. The species hovers in front of flowers like tiny hummingbirds (the flight pattern is one of the most-recognizable in spring European meadows) and feeds on nectar using the long proboscis without landing. The species' larval life cycle is one of the most extraordinary parasitoid behaviors in the insect world. Female bee flies search out the entrances of solitary bee burrows (typically Andrena mining bees and other ground-nesting solitary bees), hover above the burrow entrance, and FLICK their eggs into the entrance from above using a rapid backward kick of the abdomen. The egg-flicking behavior allows the bee fly to lay eggs in bee burrows without entering the burrow herself (which would risk being attacked by the resident bee). Eggs that successfully land in the burrow hatch into mobile first-instar larvae that crawl deeper into the burrow, find the bee's brood cells (containing developing bee eggs and larvae provisioned with pollen-and-nectar), and consume the bee's brood and provisions. The bee fly larva develops fully in the host bee burrow and pupates. The behavior makes bee flies significant parasitoids of solitary bee populations across temperate Europe and is a continuing topic of pollinator-conservation research.