How do ants and spiders count?

Chris Smith answered this...

Chris - Well, not just spiders but probably many insects can do this. The example I gave were spiders counting their steps in order to know how to build their webs but also, there was a very elegant paper that's published in Science a year or so ago by Matthias Wittlinger who's at Ulm University in Germany.

He and his colleagues were looking at how ants navigate. Ants use the sun and they also use a compass - they have in their brain a body clock and they're able to use this mental compass of the time of the sun moving across the sky to navigate by. But they also count their steps and the reason that the scientists know that for sure is that they performed the very delicate task of putting ants on stilts.

They cut hairs off the back of a pig and then glued those hairs onto the ants' legs to lengthen the ants legs, and when they did this, of course, the ants' strides became twice as long as they would normally be. When they followed the ants around, all of the ants overshot their nest because they walked twice as far as they should've done.

When they actually, paradoxically, cut the ant's legs off so they had much shorter legs, they didn't walk far enough. They're all circling around, thinking, "Where's my nest? I should be there." It was clear that they're actually counting the number of steps they've taken in order to find their way around.

In their brain and their nervous system, they must have some kind of neural integrator circuit that, every time they take a step, notches up another 1, 2, 3, and so on, so they can find their way around by counting steps. So there's the evidence: ants can do it, it's likely that other insects probably do the same.

Ben - So ants on stilts will overshoot their home! Poor ants!