Bee Fly

Bee flies make up the family Bombyliidae, a large group of true flies whose common name comes from their dense, furry bodies and bee-like appearance, an example of Batesian mimicry that likely offers some protection from predators without the fly possessing any sting. The best-known species in temperate regions, the large bee fly, is one of the first pollinator-like insects seen visiting flowers in early spring.

Despite their bee-like looks, bee flies are unmistakably flies once examined closely: they have a single pair of wings (bees have two pairs), large eyes, and a long, rigid, needle-like proboscis that projects forward from the head like a built-in straw, used to probe deep into flowers for nectar while the fly hovers in place.

Ecologically, adult bee flies contribute to incidental pollination as they visit flowers, while their larvae take on a very different, parasitic role, developing inside the nests of solitary ground-nesting bees and wasps, making the family an interesting link between pollinators and their natural parasites.

• Rotund, densely furry body that closely mimics a small bumble bee, typically tan, brown, or golden in color.
• Long, rigid, straight proboscis projecting forward from the head, used for nectar feeding without landing.
• Long, spindly legs and a single pair of wings, often patterned with a dark leading edge in the large bee fly.
• Size roughly 8–15 mm; hovers with an audible buzz and can dart sideways with great speed.
• Lookalikes: bumble bees are similar in shape and fuzziness but have two pairs of wings, elbowed antennae, and lack the fly's rigid forward-pointing proboscis.

Bee flies are found across most of the Northern Hemisphere in open, sunny habitats — gardens, meadows, woodland margins, and especially areas of bare or sparsely vegetated sandy soil near flowering plants, which provide nesting sites for the solitary bees the fly larvae parasitize. Adults are most visible in early to mid-spring, coinciding with early flower bloom.

Adults hover with remarkable precision in front of flowers, feeding on nectar and pollen through their long proboscis without landing, and darting away instantly if disturbed. Females often hover low over bare ground near bee nest entrances, flicking eggs toward the burrows. Larvae are parasitoids, entering the nests of ground-nesting solitary bees and wasps and consuming the host's larval provisions or the host larva itself as they develop.

Development follows complete metamorphosis. Eggs are flicked near or into host bee burrows; on hatching, the mobile first-stage larva seeks out a host bee cell, after which subsequent larval stages become sedentary parasitoids feeding on the host's stores or larva. Pupation occurs within the host nest, and the adult fly emerges the following spring, giving most temperate species one generation per year.