How crabs find their way home

This article on Scientific American is getting a lot of attention everywhere. It is an attempt to shed some light on how fiddler crabs figure out how far they are from home and how to get back. John Layne and his fellow student at University of Cincinnati hypothesized that crabs calculate the number of steps taken away from home multiplied by the size of each step to measure the distance they have traveled.

In one of their experiments, they allowed some crabs to take normal strides but some were forced to walk on a slippery plastic sheet so that they could not take normal strides. The results, as expected, showed that the crabs on plastic sheet came short of reaching home because they kept falling whereas the others, with normal strides, had no problem reaching their burrows. It must be then that the crabs are carrying out some complex mathematical calculations to gauge their displacement from their burrows.

The problem I have with the study is the conclusion drawn from the experiment. I am not sure if one and one make two in this scenario. Read more »