Ants Count Their Way Home

Desert ants are very good at finding their way home. How they do that has been a mystery, until now. A clever experiment in Germany finds that these ants get home by counting their steps. Ants with shortened legs stopped short of their nests, while ants outfitted with stilts walked too far.

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LYNN NEARY, host:

This is MORNING EDITION from NPR News. I'm Lynn Neary.

STEVE INSKEEP, host:

And I'm Steve Inskeep. Good morning.

This next story sheds light on one of nature's tiny mysteries, the question of how some insects find there way around. You were just wondering this, weren't you? Desert ants may wander around for hours searching for food. When they find it they make beeline back to their nest.

Now scientists have figured out how they do that, as NPR's Richard Harris reports.

RICHARD HARRIS reporting:

Ants may be tiny but they are also amazing. A desert ant can wander for hours in a featureless landscape, but it can usually finds its way straight back to its nest. These ants maintain a sense of direction simply by keeping track of all of their twists and turns.

Measuring distance, however, is a tricky business. Harold Wolf at the University of Ulm in Germany says one thought was that these ants use their eyes to measurer the rate at which the scenery is passing by. That's what bees do but not so for ants.

Mr. HAROLD WOLF (University of Ulm): You can, for instance, put them on a conveyor belt and move a visual pattern underneath them. But it doesn't alter the distance measurement of the ants.

HARRIS: So if ants are using their eyes to measure distance, what are they using? Wolf gave his graduate student, Mathias Whitlinger(ph), the crack assignment to figure out how the ants do find their way home. One thing he tried was to clip off the ends of the ant's legs. He says desert ants often lose there feet in the searing hot desert sand anyway.

The ants then set across a simulated desert in a lab, and sure enough with shorter legs they took shorter steps. And they stopped short of their nest. That suggested that the ants are actually counting there steps. But Wolf says it doesn't prove the point.

Mr. WOLF: You can always argue, okay, it hurts and the animal's injured and the animal can't walk that far anymore, so it'll stop short anyway. And so the good idea was just extend the leg.

HARRIS: They extended the ants legs by building stilts out of fine pig hairs and then gluing them on the end of the ant's legs. And as you would expect with each step on stilts the ants covered more ground.

Mr. WOLF: And in fact they did walk farther.

HARRIS: The ants with stilt legs overshot their nest. So as they report in Science Magazine, it appears that ants really are counting their steps in order to gauge distance. But of course insects aren't counting with numbers. So there must some other mechanism within the nervous system that makes that tally. Wolf has no idea what that would be.

Mr. WOLF: You'd have to record the nervous system of these animals, and they're pretty small, so that's difficult.

HARRIS: Too difficult, at least with today's technology. But it is a deeply interesting question. The answer could help explain how some animals navigate, often better than we humans can manage. Wolf says if they can figure it out, it could also be useful for building robots.

Mr. WOLF: If you want to build a robot that finds it's own around, they have to navigate, and, well, it's easy to do this in a rather coarse way. But if you really wanted to be exact and find a way exactly back to where it came from, that's quite a problem.

HARRIS: A problem that lowly desert ants have solved. If only we knew their whole secret. Richard Harris, NPR News.

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