Thursday, June 17, 2010

A Wolf in Sheep's Clothing

What looks like an innocuous bumblebee ...

... isn't a bee at all. This "bumblebee" has only one pair of wings, and upon closer inspection the head and legs also look wrong for a bee. This insect is actually a predacious bee-like robber fly belonging to the genus Laphria. In fact this species is Laphria thoracica; the field marks are the yellow hair around the wings and the orange on the legs.

One wonders which pressures of natural selection produced such a faithful reproduction of a bee. Is this the Batesian mimicry also employed by many defenceless nectar sippers, intended to dissuade hungry birds looking for lunch? Or the stealth camouflage of a lurk and pounce hunter, evolved to allow the fly to get close to its prey?

Sure enough, it wasn't long until the fly got its dinner. Robber flies will eat whatever insects they can capture and overpower, including one another, but this is the first time I have seen one actually capture and consume a bee.

Male robber flies are shorter and less robust than the females. This one got trapped in a friend's window ... and of course fooled her into thinking he was a bee. After being photographed he was shown the door and sent on his way.

Another male observed at the same locale as the female.

These are not wasps in the next three pictures, they are flies, Thick-headed Flies or Conopid Flies of the genus Physocephala, probably Physocephala tibialis. Despite its fearsome needle-like proboscis the adult is actually a defenceless nectar drinker. The larvae, on the other hand, are internal parasites of bees and wasps. Should a bee pass by the female fly will alight on it, lay its eggs, and the fly larve will hatch and ... you know the rest of the story.

Again, is the purpose of this near perfect mimicry to avoid predation? Or to lower the suspicion of a potential host? Both? Here's a photo of the real thing, a Potter Wasp.