The life of the Tunisian desert ants has to be imagined as nasty, brutal and short. Their life expectancy is just six days, they have to find their food – other dead arthropods – at temperatures of up to 60 degrees Celsius. They usually only have a few minutes on their raids before they themselves are affected by the blazing sun. So they wisely optimized two skills: their speed and their sense of direction.
A team led by Markus Knaden from the Max Planck Institute for Chemical Ecology in Jena has now demonstrated how complex the navigation skills of the ants, which are just over a centimeter in size, are. In the trade magazine Current Biology report the researchersthat the animals, in the absence of natural landmarks in the partially very flat Tunisian salt pan, build higher nest mounds so that the foraging worker ants can find their way back from their forays. The hills are like beacons in the desert.
Scientists have long known that nests in the middle of the salt pans have higher hills than on the edge of the desert, where bushes and shrubs, for example, can help with orientation. But “it’s always difficult to say whether an animal is doing something purposefully or not,” says Markus Knaden, according to a press release. The high nest mounds could also be a side effect of the different soil structure or wind conditions.
When researchers extend the legs of the ants, they overshoot the target
To test the orientation hypothesis, the researchers removed some nest mounds. In fact, the ants then found it more difficult to get home – and the animals that remained in the nest immediately began to build new mounds again. However, they failed to do so when the researchers replaced the destroyed mounds with artificial black cylinders: a lighthouse remains a lighthouse.
For their study, the researchers used small GPS transmitters, with which the path of the ants could be tracked particularly precisely. Along the way, they found other surprises. It turned out that some of the animals cover significantly longer distances than expected. A single animal covered not just a hundred meters, but in extreme cases more than two kilometers.
With such long distances, the ants are helped by their speed, a good 60 centimeters per second, and other navigation techniques that have been known for some time. Among other things, we know that they align their marching direction with the sun, they recognize location-specific smells, and they apparently have a kind of pedometer in their brain to measure distances.
Other scientists proved this in tricky experiments: If they put the ants on stilts, so to speak, with glued-on pig bristles, they overshot the mark. If, on the other hand, they shortened the animals’ legs, they overestimated the distance they had already covered and began to search for the nest entrance too early. Apparently they only count their steps and have no other sense of distance.
As great as one might find the desert ants’ precise navigation system, it does not save everyone from a sad fate, as the new study also shows. “About 20 percent of the foraging ants did not find their way back home after an extremely long run and died before our eyes,” explains lead author Marilia Freire. But it is precisely this high victim rate that could explain the high selection pressure on the ability to orientate oneself. Nature is indifferent and nasty, brutal and short the life of the desert ants.