This ant with red stilts attached to its legs was used to establish how ants know how far they have walked.

Credit: Science

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SYDNEY, 30 June 2006 - Internal step counters or pedometers may account for desert ants' ability to gauge travel distance, according to findings presented in today's issue of the U.S. journal Science.

"We have solved a long-standing and rather intriguing puzzle in animal orientation," said Harald Wolf, senior author and neurobiologist from the University of Ulm, Germany.

In ants and other insects, especially bees, a celestial compass or light cues from the sky to help them navigate their way back to their nests. But it is insects ability to measure exact distances that has remained a mystery until now.

In an unusual experiment, Wolf showed that desert ants, Cataglyphis, measure exact distances using a the number of steps they have taken. "Nobody had had an idea how to tackle even the idea of a step counter," said Wolf.

Wolf and his colleagues tested stride length by manipulating the length of ant's legs, making some ants walk on stilts (glued-on pig bristles) and others walk with shortened ‘stumps' from amputation.

Due to change in leg-length, calculating distances was significantly altered as ants with stumps were forced to take shorter strides therefore falling short of their nest, whereas the stilt walking ants took longer strides and travelled further than their nest.

Once accustomed to their new legs, the ants were able to find their nest more precisely, proposing that stride length may actually serve as an ant pedometer. The ants of course do not literally "count" their strides as a step counter suggests but rather integrate their leg movements, says Wolf and colleagues. Ants also have to take into consideration changes in stride length, such as the effect of walking with prey or changes in walking speed.

Using stride length to gauge exact distances is not a complex theory for the desert ants and has been seen not only in these ants, but humans and apes alike. "The idea of a stride counter is rather straightforward," said Wolf. "That is what we humans do if we want to measure the length of something in the range of tens of metres."