Friday, June 4, 2010

A bee or not a bee?

Our title today comes from Chapter 4 of Laurence Packer's new book, 'Keeping The Bees.'

Packer writes about the numerous 'wannabees,' the non-stinging insects that derive protection by looking like dangerous species that can sting. The photo on the right shows the hoverfly, Merodon equestris, pursuing its meal of nectar on a flower of Scabiosa and looking for all the world like some kind of bumblebee.

This kind of mimicry is referred to by evolutionary biologists as Batesian mimicry, named after the English naturalist, William Henry Bates.

The Greater Bulb Fly in the photo is a vegetarian with no sting. Its larvae feed on the roots of garden bulbs like the Narcissus. And the adults, as noted, are flower visitors, subsisting on nectar and pollen. They have no defense against insect-feeding predators like birds. But bumblebees can sting, and birds have learned to leave them alone, or suffer the consequences.

Packer provides a vivid description of the situation of an insectivorous bird. After invoking memories of the pain of a bee sting he writes, "Imagine what it would be like for a small bird or a small mammal to receive the same amount of venom in the tongue or the roof of the mouth... Having attempted to catch a bee to feed its [nestlings] the stung parent [bird] would likely be incapable of catching anything else for a long time. There is a good chance its brood would starve to death while its parent recovered."

Reason enough to avoid anything that looks remotely like a bumblebee. And thus, the harmless hoverfly is allowed to go safely about its business, protected by the fact that it only looks dangerous.

[Photo copyright D. Barr]

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