Tunisian desert ants calculate the shortest route home after a day of wandering and counting their footsteps.
Every day, Tunisian desert ants wander across the desert sands for a distance of up to fifty meters searching for the remains of a dead insect which it carries directly back to its nest - a hole no more than one millimeter in diameter.
Wehner and Srinivasan, researchers who studied the ants, found that if they moved one of these desert ants immediately after it had found its food, it would head off in exactly the direction it should have taken to find its nest if it had not been moved, and moreover, when it had covered the precise distance that should have brought it back home, it would stop and start a bewildered search for its nest.
A study by S. Wohlgemuth, B. Ronacher, and R. Wehner (Odometry in desert ants: coping with the third dimension, Journal of Experimental Biology) has shown that the desert ant measures distance by counting steps. It knows the length of an individual step, so it can calculate the distance traveled in any straight-line direction.
The ant can use dead reckoning to calculate the exact distance covered in any straight segment of the journey. It determines the direction of each segment by observing the sun. It is then possible to calculate its exact position at the end of each segment and by adding the vectors, determine the precise direction and distance back to the nest.
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