Archive for August 4th, 2010

Science Wednesday: The Ants Go Marching One by One, and They’re Counting While They Do It

by Katie Bowell, Curator of Cultural Interpretation

I think I’m going to have to cross ant-tracker off my list of possible future careers.

The other day, I noticed that the ground was full of Carpenter ants, all moving across the ground in different directions. A bunch of ants were carrying food, from a dead spider to the leg of an insect much bigger than the ant carting it, so I tried to track their movements back to their nest. Try as I might, I couldn’t do it.

Little ant, big leg of something else

To me, the ants kept moving in random zigzags and circles, following no path that I could see. And that, right there, is the key. The ants weren’t following a visible path, but an invisible one made of chemicals. Most ants navigate by leaving scent trails on the ground. These scent trails, made from chemicals excreted from glands all over the ants’ bodies, show other ants where to find food and, most importantly, how to find home again. Using chemical trails works fine in most locations, where rocks and vegetation block the wind low the ground and keep the scent trail from blowing away. But what’s an ant to do if it lives in, say, the desert? Well, if you’re Harold Wolf and Matthias Whittlinger of the University of Ulm, you think the ants are counting.

Wolf and Whittlinger, curious about how ants can navigate with no scent trails due to wind-blown shifting sands, proposed that ants may have “pedometer-like” cells in their brains that count their steps. To test the hypothesis, Wolf and Whittlinger trained ants to walk across a patch of desert to some food. Once the ants reached the food and began eating, the researchers separated the ants into three groups. One group was left alone, one group had their legs shortened, giving them a shorter stride, and the third group had their legs extended with pre-cut pig bristles – basically putting the ants on stilts and giving them a longer stride. After the meal and modifications, the ants were released to find their way back to their nest.

Ants on stilts

The ants with no leg modifications found the nest just fine. Those with shortened legs didn’t reach the nest, but stopped short and started looking for their home. The ants on stilts walked past the nest, and then stopped, looking for their home. All the ants took the same number of steps, but the changes in their gait length changed where they stopped relative to their nest, demonstrating that these ants seemed to be counting. To check the theory again, Wolf and Whittlinger put the ants back in their nest for the night, and then tracked them the next day when the ants went out for food. All the ants found food, and all the ants found their way back to the nest, showing that the internal pedometer-cells were able to readjust to the ants’ altered legs and count accurately.

As far as I know, none of the ants I watched had altered legs, so I’m sure they found their nest just fine. And good thing, too, because I still have no idea where it is.

August 2010

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