Greater Bee Fly

As has happened in previous years, this spring I saw quite a few of these small insects flying, often hovering, around the ground at Sourland Mountain Preserve. I suspect they're Large Bee-flies (aka Greater Bee Flies aka Dark-edged Bee-flies), a species of fly that:

  1. Resembles a bee.
  2. As larva, they parasitize the larva of solitary bees and wasps.

Their fuzzy, striped appearance probably has 2 benefits:

  1. Looking a little like a bee, the females may be able to inconspicuously lay their eggs around the nests of bees/wasps.
  2. Some predators might avoid attacking them thinking that they're bees who can sting, as opposed to the relatively defenseless flies that they actually are.

I suspect I see them at Sourland hovering over a dirt trail because a fair number of bees/wasps dig little nests in the ground, and these bee flies are hoping to find such a nest, flick some eggs in the vicinity of the nest, and then fly off.

They are considered hypermetamophic, a big fancy word indicating that at least 1 larval instar of a holometabolic organism is quite a bit different from the other instars. (Holometabolic is another big fancy word meaning they go through complete metamorphosis. And I'm going to ignore that metamorphosis is also a big fancy word for the sake of brevity.) In the case of the Greater Bee Fly, being hypermetamorphic allows their 1st instar to have the mobility to crawl over to a bee/wasp larva to feed on it. (It's helpful if the larva's mother was able to fling her eggs very close to a bee/wasp nest.)

With a name like Greater Bee Fly, you're probably thinking that there should be an even smaller Lesser Bee Fly out there, and you'd be half right. There is a Lesser Bee Fly, though it's unclear that it's smaller than the Greater Bee Fly. My sources say that the Greater Bee Fly is 6-12 mm in length, while the Lesser Bee Fly's length is reported as 5-14 mm, suggesting the lesser is often about the same size, and could actually be slightly larger.

April 14, 2023 at Sourland Mountain Preserve
Photo 272129225, (c) jpviolette, some rights reserved (CC BY-NC)

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