Ants on stilts.

If you want to know how far you've walked, you can choose among several strategies. You can measure your route on a map. You can wear a handy gadget, such as a GPS device that calculates distances or a pedometer that counts your steps. Or you can ask someone who already knows the answer.

It turns out that people aren't the only animals with distance-measuring skills. Certain ants have a built-in pedometer that tells them how far it is from here to there.

Scientists from the University of Ulm in Germany studied an African ant called Cataglyphis fortis. These ants live in the Sahara desert, where they zigzag around until they find food. After they find something to eat, the insects take a more direct route home.

Previous research had found that these ants use the position of the sun and light in the sky to figure out which way to go.

Scientists had also proposed that the ants might measure distance based on the length of their strides. The German researchers were the first to test this idea. In Tunisia, a country in Africa, they trained ants to run between a nest and a feeder along a 10-meter-long (33-foot-long) runway.

After the ants had learned the route, the scientists captured some of the crawly creatures at the feeder. They trimmed some of the ants' legs to make their strides shorter. They glued on bristles to make the legs of other ants longer.

Then, they put the ants on a runway next to the one they had used for practice. The ants picked up where they left off-grabbing crumbs and heading back home.

Their new limbs tricked the ants, however. Those with clipped legs started looking for the nest after walking only 6 meters (20 feet), instead of the usual 10 meters (33 feet). The ants with lengthened legs scurried for 15 meters (49 feet) before looking for home.

It appeared, the scientists say, that the ants were using the number of steps they took, not the actual distance traveled, to gauge how far they had gone. After a few days with their new legs, however, the ants seemed to reset their pedometers. Their sense of distance was once again restored.