GERMANY: Mapping the world by smell

Humans have long admired the humble ant for its organisational abilities and strength. Now researchers have found another reason to respect the insect - some of them can smell 'in stereo' and use the ability to find their way home.

Scientists at the Max Planck Institute for Chemical Ecology in Jena have been studying the navigational skills of desert ants, Cataglyphis fortis, from Tunisia. The ants are known to use the sun as a compass, count their steps and use visible landmarks to find their nest after looking for food. But after the research team from Jena found that the ants also used smell to find their nests, they conducted new experiments.

They revealed the insects could not only find the source of an odour, they also use the distribution of different odours near their nests in a map-like manner. The scientists found the ants need both of their antennae for this navigation-by-smell - essentially smelling the scenery in stereo.

"We conducted two key experiments," says Kathrin Steck, a PhD student at the institute. "First we marked four odour sources surrounding the nest entrance with the substances methyl salicylate, decanal, nonanal, and indole, and got the ants trained on them.

"If these four odour points were shifted away from the nest in the original arrangement, the ants repeatedly headed for the odours, even though the nest wasn't there anymore. If we rearranged the odour sources relative to each other, the ants were completely confused."

Therefore the researchers assumed that ants do not "think" one-dimensionally - that is, they do not associate the nest with only one smell - but multi-dimensionally: they relate an odour landscape to their nest.

Working on the basis that spatial perception requires the use of two sensory organs, the scientists tested ants that only had one antenna. Markus Knaden, leader of the study, said they found that such ants could not use the odour landscape for navigation.

Stereo smelling in animals is not new - rats and humans are thought to have the ability too. This new study shows that ants smell in stereo but not also that they can use the ability for navigation.

The research was published in Animal Behaviour last month.