Ant steps

Ants are almost everywhere on our planet, even the hot and barren desert. And one of the ants that live there is appropriately called the Desert Ant (Cataglyphis fortis).

These ants are very well adapted to this harsh environment. Food is very scarce, and ants often have to walk very far in order to find something edible to bring back to the nest. However, when they want to return to the nest…a problem arises: it is very hard to navigate in a desert, as everything looks alike. Normally chemical trails would be used, but these don’t stay around for very long in the desert. So, these ants found another way of navigation!

First of all, while they are searching, they often stop for a while, taking a mental picture of the environment (especially the position of the sun). The sun is a good indicator to know in which direction you’re walking, however, the ants also need to know how far away from the nest they are. In order to do this, they actually seem to calculate how many steps they need to take to get home!

So…how did scientists find this out? In a very smart way actually! By picking up an ant when it is about to return to it’s nest, and extending the legs using pig-hair (a bit like our wooden stilts), these ’extended’ ants make bigger steps than normal ants. These ants started running back to the nest…and promptly run further than they actually should! With other ants, instead of extending the legs, they cut off a piece of leg instead. These ants make smaller steps, and started thinking they were near the nest way to early.

Cataglyphis fortis individuals with either their legs cut (left) or extended (middle); or normal untreated individuals (right). Photo copyright Matthias Wittlinger.

Cataglyphis fortis individuals with either their legs cut (left) or extended (middle). Normal untreated individuals are on the right. Photo courtesy of Matthias Wittlinger.

Conclusion: Desert ants have a build in ‘odometer’, which they use to calculate how many steps they need to take in order to get home.

I wonder if they ever lose count…

Source: Wittlinger et al. (2006) The ant odometer: Stepping on stilts and stumps. Science 312:1965-1967

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