Zeroing in
Bees seem to grasp the numerical concept of zero - the first invertebrate we have found that can do so.

When the insects were encouraged to fly towards a platform carrying fewer shapes than another one, they apparently recognised "no shapes" as a smaller numerical value than "some shapes".

Zero is not an easy concept to comprehend, even for us. Young children learn the number zero later than other numbers, and often have trouble deciding whether it is less than or more than 1.

Apart from us, some other animals grasp the concept of zero, though. Chimpanzees and monkeys, for instance, have been able to consider zero as a quantity when taught - and a grey parrot called Alex learned the concept.

With their tiny brains, bees may seem an unlikely candidate to join the zero club. But they have surprisingly well-developed number skills: a previous study found that they can count to 4.

To see whether honeybees are able to understand zero, Scarlett Howard at RMIT University in Melbourne and her colleagues first trained bees to differentiate between two numbers.

The team set up two platforms, each with between one and four shapes on it. On one platform, bees were given a sweet sucrose solution, and on the other a nasty-tasting quinine solution. The researchers trained the bees to associate a platform that had fewer shapes on it with the sweet reward, until they made the right choice 80 per cent of the time.

Next, the bees went through a test phase involving neither rewards nor punishments. They were given a choice between two or three shapes on one platform and "zero" shapes on the other. The bees picked zero most of the time.

In a second experiment, other bees were trained in the same way, but this time they had to choose to land on a platform with either zero or between one and six objects. They consistently chose zero, but were less accurate and took more time when the other option was one rather than six objects.

This may be an important observation: the numerical distance between the two quantities on offer seemed to affect how challenging the bees found the problem. This seems to suggest that the bees conceive zero as a number, close in value to 1, and not simply some non-numeric quality.

Howard shared the findings at the Behaviour conference in Estoril, Portugal, last week.

Such experiments suggest that bees' comprehension of zero is similar to that of humans and some primates, she said. But it's unclear why they have this ability. "We still have some things to figure out about why they can do this," said Howard.

Few attempts have been made to test whether animals other than primates can recognize zero as a number, says Susan Healy at the University of St Andrews, UK. "The notion that an invertebrate did it would overturn the books quite a lot," she says.