28 January 2009

Bees can count up to four, study shows

Cosmos Online
A new revelation about the numeracy of insects has come out of a study from the Australian National University.
Worker bee

Busy bee: The experiments demonstrate the remarkable learning power of social insects, which have to go out foraging over long distances. Credit: iStockphoto

SYDNEY: A new revelation about the numeracy of insects has come out of a study from the Australian National University.

In an elegantly designed experiment researchers led by Shaowu Zhang, of the university’s Vision Centre have shown that, at a glance, bees can discriminate between patterns containing two and three dots.

And, with a bit of tutoring, they can learn to tell the difference between three and four dots. But after that, according to a study detailed today in the journal PloS One, bee maths seems to run out. The team found their honeybees couldn’t reliably tell the difference between four dots and five or six.

Counting landmarks

Earlier work had “demonstrated that bees can count up to four landmarks on their way from their hive to a food source,” said Zhang. “This new research shows they can tell the difference between different numbers – even when we change the pattern, shape or the colour of the dots.”

For the study, conducted in collaboration with researchers at Wurzburg University in Germany, bees flew though an entry marked with a pattern of either two or three dots, which were signposts to a reward.

They then had to choose between two patterns by correctly matching the number of dots, to find where the reward was. A feat they then managed to repeat reliably once they had learned that two dots at the first entry meant they had to look for two dots at one of the second pair of patterns, where the reward was hidden.

Careful control over the experimental environment showed the bees were not using colour, smell or other clues to find their way to the hidden sugar-water reward.

Stars and lemons

Presenting blue and yellow dots, stars and lemons, or random patterns didn’t fool the insects, which continued to reliably navigate their way to the reward once they had figured out and memorised what the signs meant, based on number.

“Bees can definitely recognise the difference between two, three and four – although four a little less reliably,” Zhang added. “This is a process known as ‘subitizing’, which means responding rapidly to a small number of items.”

The experiments demonstrate the remarkable learning power of social insects, which have to go out foraging over long distances – the ANU team has tracked bees over distances as great as 11 km – and then find their back to the hive, and out to the food source again reliably.

Zhang said the ability to discriminate between different numbers is part of this navigation, perhaps as bees pass clumps of two trees or three trees on their way to the food source, or use similar patterns among flowers or other landmarks as they draw close to it.

“There has been a lot of evidence that vertebrates, such as pigeons, dolphins or monkeys, have some numerical competence – but we never expected to find such abilities in insects,” he said. “Our feeling now is that, so far as these very basic skills go, there is probably no boundary between insects, animals and us.”

The tantalising question is whether bees can actually perform elementary arithmetic – and the researchers are already planning an experiment to explore it.

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More information:
The study in PLoS One
With the Public Library of Science (PLoS).
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