Ants on stilts take longer strides than their normal counterparts (Image: Science)

Desert ants have an internal system – like a pedometer – that keeps track of how many steps they take, according to a new study. The insects seem to rely on this system to find their way back to the nest after foraging. Other insects may also possess this pedometer-like system.

Some types of ant appear to use visual cues or leave scent trails to find their way home. But desert ants have a remarkable ability to retrace their steps from their nesting site even though they travel on flat terrain that is devoid of landmarks, and any odours quickly fade in the hot temperatures.

Previously, researchers have found evidence that ants use the position of the sun as a compass (see Nature, DOI: 10.1038/293731a0). But, as Harald Wolf at the University of Ulm, Germany, and his colleagues point out, for such a compass to be of use desert ants would need a way to track distance.


Wolf and his colleagues became interested in the mystery while studying Saharan desert ants (Cataglyphis fortis). When the researchers shortened the ants’ legs the insects had trouble finding home.

Food source

They decided to measure how much the modified ants over- or underestimated distances. First, they allowed unaltered ants to learn the distance between a nesting site and food source separated by a 10-metre aluminium channel.

After a set time the ants were removed from the food source and immobilised temporarily in a wax-like material. Wolf’s team then either removed about 1 millimetre from the tips of the insects’ legs or attached 1-millimetre “stilts” made of lightweight bristles.

The ants were then placed back at the feeding site and allowed to return to their nest along another aluminium channel – which did not connect to the nest.

The researchers found that ants walking on stilts typically travelled 50% further than the normal distance and then began pacing back and forth looking for home.

And those with shortened legs paced back and forth in the channel after travelling, on average, only 50% of the normal distance to the nest.

Watch a video of ants on stilts trying to find their way home (3.5MB .mpg file).

Internal system

Wolf says that the findings show that ants have an internal system that somehow keeps track of now many the steps they have taken, though he is quick to point out that the insects probably cannot “count” as such.

He suspects that the ants’ automatic step counter is part of their nervous system and that it gets reset each time they return to the nest.

The fact that ants with altered legs correctly estimated the distance home on future trips out from the nest supports Wolf’s speculation.

Ant expert Deborah Gordon of Stanford University in California, US, calls the new findings “very exciting”. “I hope it will stimulate others to learn how general this is among the 10,000 to 12,000 species of ants,” she adds.

Journal reference: Science (DOI: 10.1126/science.1126912)