Dear Readers, the life of a desert ant is a dangerous one. The species in today’s study, Cataglyphis fortis, lives on the salt flats of Tunisia, where temperatures are high and food scarce. There are predators everywhere, and it’s estimated that the life of an average adult ant is only 5 to 7 days. They can run at the equivalent of 600 km per hour, which helps to avoid the worst effects of overheating, but their big challenge is finding their way back to their nests, which have entrances which are only the size of a thumbnail, when their foraging trips can be up to 2 kilometres. Many animals navigate by using landmarks, but the saltpans are completely flat, so it was thought that this was not an option. So, how do they do it?
The Tunisian ants have been studied for over fifty years, and the first takeaway seems to be that the ants navigate by ‘dead reckoning’ – they keep a tally of both direction and distance, so that they can calculate their way home. Researcher Rüdiger Wehner notes how the ants turn back to memorise the precise location of the entrance to their nest before setting out to forage. The ant seems to use the polarisation pattern of the sky, the wind direction and the Earth’s magnetic field as its compass, and it seems to be aware of the number of steps that it takes – when Wehner attached tiny stilts to the legs of ants (and goodness only knows how that was done) the ants ‘miscalculated’ because their stride length was longer. Wehner was so impressed that he wrote a book about the ants, called ‘Desert Navigator‘ which is available in English and with some fine photographs for all you formicophiles out there.
The latest news, however, comes in a study by Markus Knaden at the Max Planck Institute for Chemical Ecology in Germany. Knaden and his team noticed that the ants built mounds, both around the edge of the salt flats, where they were barely noticeable, and in the centre, where they could be up to 25 centimetres high. Could this be something to do with navigation? Like scientists do, they decided to remove some of the mounds and leave others alone. When the mounds were removed, mortality amongst these already beleaguered ants rose by between 250 and 400 percent, and it was noticed that the ants started rebuilding the structures as soon as they were destroyed. So, it appears that the ants not only have an inbuilt system of navigation but they build their own landmarks. Sounds a lot like tool-use to me. I find it amazing that not so long ago, we thought that humans were the only animals to use tools, and now it seems as if every class of animals has some variant on the process. Nature never ceases to amaze.