From  Nature News Services |
Ecology
: Out of the strong came forth sweetness By Henri Gee |
"The
mimicry between droneflies and honeybees has been fooling humans for over 2000
years," say Y. C. Golding and M. Edmunds of the University of Central
Lancaster, Preston, UK, who have just worked out why.
Ancient Egyptians and Greeks thought that bees were born from the rotting carcasses of cattle. It even got into the Bible (Judges, chapter 14, verse 8). Strongman Samson tore a lion in two while on the way to woo a prospective bride among the Philistines. On his return, "there was a swarm of bees" in the lion's broken body.
Not until 1898 did entomologists recognize that these bees born of decay and death are, in fact, droneflies -- insects more closely related to houseflies and bluebottles than bees. Droneflies lay their eggs in ditches and sewers, and adults 'mimic' bees to fool potential predators.
A harmless fly that looks sufficiently like a bee causes a hungry bird to hesitate for long enough to allow the fly to flee. Indeed, wherever bees go, they are followed by a gaggle of 'false bees' -- droneflies, and other insect impostors -- hoping to cash in on the bees' stinging reputation.
But to the trained human eye, droneflies and bees are different. And some birds, with their far sharper vision, can tell a bee from a dronefly ten metres away, so who do the droneflies think they're fooling?
Golding and Edmunds report in Proceedings of the Royal Society of London that what droneflies lack in appearance they make up for in behaviour: they may not talk the talk, but they can walk the walk.
The researchers watched bees, droneflies and other insects about their business in a variety of summertime settings, from a glade by a river bank, to plantings in city-centre parks. Unlike other insects, droneflies spend as much time in flowers, and the same amount of time flying between flowers, as bees. This bee-like behaviour could be enough to prompt second thoughts in the minds of predators.
There is, however, a fly in the ointment.
For this kind of mimicry (known as 'Batesian' mimicry) to work, the theory goes that the mimic must be substantially rarer than the model. The rationale is easy: a bird won't risk pecking a stripy insect if it is likely to be a bee, so the mimic's disguise remains intact. However, if harmless mimics outnumber the models, birds will soon rumble the deception and pluck up courage to attack -- safe in the knowledge that the prey is more likely to be harmless.
At several of the sites examined by the researchers, droneflies substantially outnumbered real bees, and yet the droneflies still seemed to be benefiting from looking, and behaving, like bees. The researchers suspect that what we are seeing is an unstable situation, a result of human disturbance.
Droneflies, like rats, cockroaches, tuberculosis and other familiars of corruption, are camp-followers of humanity. The recent spread of human beings (and their nasty habits) across the globe has generated unprecedented opportunities for droneflies to breed. So although mimics now mob bee models, predators, it seems, have yet to twig.
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