Bumblebees outwit robotic spiders

By Elizabeth Mitchell Science reporter, BBC News

Bumblebee vs Robotic Crab Spider

Scientists have found that bumblebees learn from their "near-death" encounters with crab spiders and adapt their future foraging strategies.

They watched real bees in an artificial meadow - containing yellow "flowers" and robotic crab spiders.

Bees that had been "captured" spent longer inspecting flowers during subsequent foraging trips.

They may outwit the spiders - but at the expense of valuable foraging time, Current Biology reports.

Crab spiders lie in wait on flowers, ready to ambush their "most prized prey" - the bumblebee.

This cryptic predator has an amazing ability to change its colour to closely match the flower it is lurking on.

Scientists wanted to know if bumblebees adapt their foraging behaviour after encountering a crab spider.

Artificial meadow

Dr Thomas Ings and Professor Lars Chittka from the Queen Mary University in London created a "meadow" with artificial yellow flowers.

"The bees behave very much as they do in nature: they go from one flower to the other as they empty it of food," Dr Ings told BBC News.

"Dangerous" flowers harboured life-sized, robotic crab spiders with two remote-controlled, foam pincers.

The bees were introduced to a meadow containing well hidden (yellow) or highly visible (white) spiders.

"We thought it would be more difficult for the bees to learn to avoid camouflaged spiders," explained Dr Ings.

"However, the bees learned to avoid both types of spider equally well - and very quickly," he said.

Trade-off

A 3D video tracking system revealed that although the bees became very accurate at detecting the camouflaged spiders - they also became increasingly wary.

"When they come in to inspect flowers, they spend a little bit longer hovering in front of them when they know a camouflaged spider is present," said Dr Ings.

"Cautious" bumblebees spend longer inspecting flowers

With this "trade-off", the bees may lose valuable foraging time - but they reduce the risk of becoming the crab spider's next meal.

Their memory does not fade: the next day the bees rejected all yellow flowers - even those without spiders.

These "false alarms" may have a knock-on effect on pollination - bees may ignore a whole patch of flowers if they know it contains a high number of camouflaged spiders.

The bees that detected the highly visible (white) spiders did not change their flight behaviour.

It is unclear why the crab spider uses so much energy to change colour - especially when this strategy seems to make their prey more cautious.

"It might be that camouflage reduces the chances of the crab spiders being eaten by their own predators," suggested Dr Ings.

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