I thought this story about determining how Saharan desert ants navigated was kind of a neat proof (ignoring the cruelty to ants aspect).
Most ants navigate by scent trails, but the Saharan ants, like bees, use the Sun. However like mariners before they could determine longitude, they also need to be able to keep track of how far they have gone. The century old hypothesis was that the did this by counting the steps. How to test this? Let the ants get the distance, and then change their stride length.
Some ants, when they arrived at the feeding station, had the ends of their legs amputated, to shorten their stride length. Others were fitted with stilts in the form of pig-bristles glued to their feet. Both lots were then returned to the feeding station, to make the journey home.
As predicted, the ants on stilts, whose stride-length meant their internal pedometers had not clicked enough times, walked blithely past their nests, and were left stranded almost five metres on the far side before they started looking for the hole. Meanwhile, the poor stumped ants travelled only about six metres before they started their search.
The story, however, has a happy ending. Having proved his point, Dr Wittlinger returned both stumped and stilted ants to the nest and gave them a few days to recover. Then he let them out for another run. Now that they could re-count their outbound journeys, they were able to calculate the journey home correctly. Ants may not be very bright, but it seems they have a head for figures.