Taking the short way home

Ants have sophisticated odometers

Last Updated: Saturday 04 July 2015

desert ants ( Cataglyphis fortis ), renowned for their ability to perform large-scale foraging excursions and then return to the nest by path integration, do so by integrating courses steered and the distances travelled into a continually updated mapping method. Whereas the angular orientation is based on cues taken from the skylight. New research shows that ants are bale to calculate the horizontal distance along the ground even while they are made to travel up and down a route along the ground.

The research conducted by Sandra Wohlgemuth, researcher at the Institute of Biology, Humboldt-University, Berlin, and other colleagues, showed how the ant's biological odometer operates when a path integration task has to be accomplished that includes a vertical component.

The researchers trained ants within arrays of uphill and downhill channels, and later tested them on flat terrain. In all these cases, the ants indicated homing distances that corresponded not to the distances actually travelled but to the ground distances.

Saharan desert ants leave their underground colonies for distances of several hundred metres, winding their way in a tortuous search for food, but then return to their point of departure along an amazingly straight path. They accomplish this task by integrating information about the angular and linear components of movement, information that humans need a compass and an odometer to calculate. The ants' compass, which exploits polarisation and spectral gradients in the sky, has been studied in some behavioural and neurophysiological detail but attempts to unravel the ant's odometer have so far met with limited success.

In a first experiment, researchers trained ants to walk over a series of hills, experimentally mimicked by a linear array of nine uphill and downhill channels until they reached a feeding site. The distance travelled by the ants within these tilted channels was 8.7 m, corresponding to a ground distance of 5.2 m. When later tested within a horizontal channel, the ants taken from the feeder walked for a distance of approximately 4.7 m. Then they made a sharp U-turn and started long-lasting oscillating search movements about that point. The distance travelled by the ants in the flat channel was much shorter than the one travelled by them during their runs across the hills. This finding is corroborated by the reciprocal experiment, in which the ants were trained to walk for 5.2 m within the flat channel and were later tested in the hilly array. The results proved that when the ants walk along an uphill and downhill path, their odometer records the ground distance rather than the distance actually travelled.

How the ants are able to achieve a task that humans need calculus and computing equipment to work out is yet not known.

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