Technology & Science

Ants walk using internal distance clock: study

Desert ants have an internal pedometer that measures how far they've marched, say researchers who manipulated the length of the insects' legs to check if insects can count steps.

Desert ants have an internal pedometer that measures how far they've marched,researchers have found.

Foraging Sahara Desert ants wander when searching for food, buttake a relatively straight path when heading back to their nests.

To do so, the ants need to judge directions and distances when travelling over flat, sandy terrain without landmarks. Scent trails used by other species won't work because the odours fade in the hot desert.

Previous studies suggest ants use cues from the sky to orient themselves, but scientists don't know how the insects track distance.

In the early 1900s, researchers proposed that ants use a pedometer or step integrator.

To test the idea, Harald Wolf at the University of Ulm inGermanyand his colleagues shortened and extended thelegs of 50 ants to see how they measure distance. Their findings are in Friday's issue of the journal Science.

The ants were trained to walk 10 metres from their nest to a feeder.

Stilts and stumps

When the ants reached the feeder, researchers glued one-millimetre stilts on some ants, severed the legs of others by one millimetre, or did nothing. (Ants often naturally lose legs as they age.)

For the homeward journey, ants travelled along another journey that did not connect to their nest. That way, scientists could tell if ants "counted" steps to make their way back to the nest by a predictedamount.

As expected, manipulating the length of legs scrambled the ants' pedometer. Ants walking on stilts walked 10.55 metres to return to the starting point, and ants with shortened legs took 10.25 metres.

"These results support the hypothesis that desert ants use a pedometer for distance measurement, or a step integrator [loosely speaking, a step counter, although the ants most probably do not literally count]," the researchers wrote in Science.

Ants on stilts also travelled slightly slower than normal, presumably because of the extra load. High-speed video recordings showed changes in the actual stride length.

And ants with manipulated legs correctly estimated the distance home during subsequent trips, lending support to the pedometer hypothesisfor the new stride length.

Further studies are needed to find the mechanism behind the pedometer, such as how the nervous system registers the limb movements, the researchers said.