Wednesday, April 10, 2013

Bee flies

If you've spent much time afield, investigating spring wildflowers, you've doubtless noticed the strange beast shown here. These odd insects suggest animals far removed from their lineage, such as little hummingbird moths, or bees. Neither, nor.

This is a bee fly. Yes, a fly. I photographed the one above a few years back, as it drew nectar from the staminate (male) flowers of Pussy-toes, Antennaria plantaginifolia. Bee flies are rather hard to photograph when on the roll, as they are awesome fliers and quick to dart and dash about.

On my recent trip into the depths of the I'on Swamp in South Carolina, I happened along a sandy, sunny woodland gap that had several bee flies on the wing. So, I devoted some ten minutes of my life trying to get decently clear images of the insects in flight. A few of them came out; most were deposited in the recycle bin.

This species, I believe, is the same as in the prior photo and it is the big boy of the crowd: the aptly named Large Bee Fly, Bombylius major. Keep in mind, "large" is a relative term. These things look like a miniature jelly bean covered with fur, and I suppose an aeronautics engineer would take a glance at one and proclaim that it should not be able to rise aloft.

But fly they do - these things are the Blue Angels of the fly world. This particular bee fly was diligently guarding a patch of turf, and whenever another bee fly would foolishly impinge on its territory, this fly would dart after it with an impressive burst of speed, astonishingly fast jags and jigs, and a clearly audible chainsaw buzzing of the wings. Note its long proboscis, the better to suck nectar from plants.

This is some sort of solitary bee, or digger bee, in the act of creating her burrow. Into said burrow she will deposit a sweet ball of plant pollen, and lay an egg along with the pollen. Then the chamber is sealed. Life for the digger bee grub seems unusually Disneyesque for an insect. The bee larvae hatches to what amounts to a giant sugar ball; it is as if the grub is born into cotton candy and must eat its way out. What could possibly go wrong?

Enter the "cute" Bombylius major, that adorable little fuzzy hummingbirdlike fly. Like the digger bees, this fly too collects much pollen and as with the bees, is undoubtedly an important pollinator. But the Large Bee Fly is a digger bee's worst nightmare.

When the time for reproduction rolls around, the female bee fly sneaks over to a digger bee's burrow before it's sealed, and hurls her eggs at the entrance. I'm not sure exactly how she "hurls" them, but whatever the means of locomotion, if her aim is good the eggs either tumble into the burrow or land near its entrance.

Upon hatching, the predatory fly larva - which probably lacks any sort of the cuteness of the adults - begin feeding on the pollen provisioned by the hard-working digger bee. When that's exhausted if not before, the fly larva digs into the digger bee grub and feasts on that. Life in the bee burrow becomes quite the horror show, thanks to the bizarre reproductive strategy of one of our most charming flies - indeed, a fly that anyone would like! - the Large Bee Fly.

1 comment:

Julie at Aldaron said...

Fascinating! I just saw one or two of these out in my SW Oregon pasture. Have never seen one in my life, as far as I can recall. I watched it awhile, then it followed me back along the path, watching me, too. Amazing creature. So glad you share the reproductive history!