Counting Steps with Ants

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Counting steps with ants reported in ScienceNOW 29 June 2006 and BBC News, 30 June 2006. Biologists have wondered how ants that live in places with unvarying terrain such as sandy deserts are able to find their way back home after foraging far from the nest. Previous studies have shown they can memorise the position of distant landmarks to keep track of which direction they are facing, but when they find food they don't just retrace their steps, they head straight back to the nest. Therefore they need to have some idea of how far they have moved and how far it is back to the nest.

Ant watchers have also observed that an ant's stride length is always the same, so they wondered if the ants kept track of the number of steps as an indicator of how far they have moved, and how far it is back to the nest. A team led by Matthias Wittlinger, of the University of Ulm, Germany, established an ant nest outside their laboratory and watched as the ants went foraging. They collected ants that had ventured a long way from the nest and modified the length of the legs of some of them. The researches extended the leg length of some ants by gluing tiny stilts to their legs. This meant that each step would be longer. The researchers clipped off the ends of the legs of another group, so that their steps would be shorter. The rest of the captured ants were left with normal length legs. The researchers then placed the ants back where they found them, gave them some food and watched them make their way back to the nest.

The long legged ants went beyond the nest before starting to look for the entrance, the short legged ants stopped too soon, and the normal legged ants made it home. To confirm that it was the number of steps that was guiding the ants the researchers returned the modified ants to the nest and then observed them on another foraging trip. This time they returned to the nest as normal. Mandyam Srinivasan, a biologist at Australian National University in Canberra commented: "The challenge now would be to discover exactly how the nervous system senses and integrates the limb movements to provide the ant with a sense of how far it has travelled."

BBC

Editorial comment: Anyone who failed trigonometry at school should be impressed by these ants, because it involves more than just counting steps, since they don't follow their own trail back and so took a different number of steps out than back. When the ants go out foraging they do not travel in a straight line until they find food, but may have changed direction many times. Therefore, when calculating the number of steps to get back home they have to take into account the angles at which they moved and keep track of how many steps in each direction. We are sure an engineer could invent a device that could count steps, measure angles and calculate distances, but if one does no-one will claim the invention evolved by chance. Therefore the biologists who carried out the experiment described above have no excuse not believing that ants were created by a smarter engineer. We are also wondering when the Ants Rights people will begin to sue on behalf of leg deprived ants whose legs have been trimmed. (Ref. insects, arthropods, mathematics)

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