Some ants have figured out how to avoid getting lost: build taller anthills, according to a recent study.
Desert ants living in the hot, flat salt pans of Tunisia spend their days looking for food and reach as far as 1.1 kilometers from their nests. To find their way home, desert ants use a navigation system, relying on the sun's position and counting their steps to track their location relative to their nest.
But this system becomes increasingly unreliable as the distance from the nest increases. "We realized that, whenever the ants in salt pans came closer to their nest, they suddenly pinpointed the nest hill from several meters distance," says Markus Knaden, a researcher at Max Planck Institute for Chemical Ecology. "This made us think that the hill serves as a nest-defining landmark."
So Knaden and colleagues captured ants from nests in the middle of salt pans and from along their shorelines. Only salt-pan nests had distinct hills, up to 40 centimeters tall, whereas the hills on shoreline nests were lower or barely noticeable. Next, the team removed any hills and placed the captured insects some distance away from their nests. Salt-pan ants struggled more than shore ants to find homes. Shore ants relied on the shoreline for guidance and weren't affected by the hill removal, the researchers concluded.
The team further conducted another study to see if desert ants were deliberately building a taller hill when their surroundings lacked any visible landmarks. So, the researchers removed the hills of 16 salt-pan nests and installed (安装) two 50-centimeter-tall blocks near eight of them. The other eight nests were left without any artificial visual aid. After three days, the researchers found that seven ants from the unaided nests had rebuilt their hills. But only two ants from the nests with man-made blocks nearby had bothered to rebuild.
"It implies that ants regularly assess the complexity of their environment and change their decisions based on their conclusion," says ecologist Judith Bronstein of the University of Arizona.
