Family Bombyliidae – Bee Flies

Family Bombyliidae – Bee Flies
Live adult bee flies photographed in the wild at DuPage County, Illinois, USA.
Bombyliidae larvae are almost all predators of the larval stages of other insects.

Bee Fly - Bombylius major
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Bombyliidae is one of the largest families of Diptera, with over 5,000 valid species described worldwide. Their high diversity may be due to the parasitoid habit of the majority of their larvae. Adults feed on nectar and pollen, and are believed to be important pollinators of many plants, although few species have been studied in detail. Bee flies occur on all continents except Antarctica, however their highest diversities occur in semi-arid and arid environments (Hull, 1973).

Bee flies do not bite or sting and are completely harmless to humans and their pets.

The family includes a wide variety of morphological forms, such as the large Palirika marginicollis (Gray), with iridescent green-blue body scales recalling those found on the wings of a Morpho butterfly, and striking black and hyaline wings spanning 45 mm; and the tiny, delicate, humpbacked yellow and black species of Glabellula Bezzi with hyaline wings and a body length about 1 mm.

Bombylius major
Bombylius major

Scaly Bee Fly – Lepidophora lepidocera

Bee Fly
Bee Fly – Villa sp.

Bee Flies have pubescent (hairy) bodies and long, slender legs. The proboscis is long, points forward, and is adapted for feeding on flower nectar.

I most often see Bombylius major nectaring at dandelion in early spring, a flower that seemingly does not need such a long proboscis. It may be that the flowers with long corollas upon which these flies fed during their long evolution have gone extinct, or are merely absent from Chicago suburban environs.

Anthrax sp.

Eggs are laid near the entrance to the nest of the specific bee host parasitized by that species of bee fly. The tiny larvae enter the nest and usually wait until the bee larva has pupated before metamorphosing from a small, mobile animal to a smooth, fat larva which feeds on the bee pupa. The bee fly pupa is dual-phased. The first pupa is ‘normal’; the second has a sharp battering ram with which to break down the cell wall made by the adult closing the cell.

Bee Fly, Poecilanthrax willistonii
Bee Fly, Poecilanthrax willistonii photographed near Newspaper Rock, Canyonlands National Park, Utah.

Bee flies are said to resemble long-legged bumble bees, but I've never seen that connection. There are Syrphid flies and robber flies that do a much better job of impersonating bumble bees. Bee flies much prefer to hover in midair while doing their nectaring, undoubtedly to avoid capture for those who lurk about flower blooms looking for an easy meal, such as the ambush bugs and the crab spiders. Adult bee flies become active about the third week in April, here in northern Illinois.

I most often see bee flies hovering around flowers, or if resting, usually on the ground, on bare soil. They are extremely wary and difficult to approach. No doubt their large compound eyes give them good vision, plus they have that air-motion sensing mechanism that helps the ordinary house fly avoid the swatter. Adult bee flies drink nectar, but the larvae are parasites of beetle larvae as well as the brood of solitary wasps and bees, the hole or burrow-nesting insects. I've often seen female Bombylius sitting in very loose soil, vibrating their butts like mad, so that the dirt is actually thrown outwards (below). One source says these flies are "gathering sand to coat their eggs," to keep them from drying out. I've seen syrphid flies do the same thing.

Bee Fly vibrating her butt in the sand.
Bee Fly "Egg Coating"

Good thing these flies don't bite or sting. All in all, a fascinating insect worthy of study. Next springtime, why not take a trip to the woods? You'll find these gals busily gathering nectar from the dandelions along your favorite sunny path.
Systoechus vulgaris
Systoechus vulgaris

  1. Chen Young, Carnegie Museum of Natural History, “Crane Flies of Pennsylvania
  2. P. Oosterbroek, “Catalogue of the Craneflies of the World
  3. University of California, DANR, "Biological Control Agents for Aphids in Vegetable Crops"
  4., “Family Tachinidae
Flies of North America – Order Diptera. Flies are prevalent in virtually all habitats, with over 16,000 species in North America. Flies can be distinguished from all other insects in that they only have one pair of normal wings. Most flies have compound eyes and mouthparts adapted for piercing, lapping or sucking fluids.
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