How Desert Ants Find Their Way Home Backwards: Sun and Memory Navigation

Spanish desert ants (Cataglyphis velox) exhibit remarkable navigation skills when transporting oversized prey back to their nest, even while moving backward. How do these ants find their way home when their heads are not facing the destination? Scientists initially suspected that ants needed to occasionally turn around to orient themselves with familiar paths. Indeed, the behavior of ants placing their prey, facing their direction of travel, and then resuming dragging was observed. However, research on Cataglyphis velox suggests that ants also utilize information gathered during their outward journey from the nest. While walking forward, ants can remember turns, changes in direction, and the number of steps taken. This process is referred to as 'path integration,' which helps ants keep track of their position. Furthermore, ants use the angle of the sun to determine their location and recognize landmarks along their route. The question for researchers was how this information is used when ants must return home by walking backward. Sebastian Schwarz and his colleagues observed ants that had traveled from their nest to a feeder. They then provided the ants with large cookie crumbs to drag back to the nest. In some experiments, the researchers altered the scenery along the path by placing black plastic bags and tarps. These changes affected when the ants stopped to orient themselves. Ants that encountered the new scenery turned around after dragging the food for approximately 3.2 meters on an eight-meter path. Conversely, ants on their usual route could move nearly six meters without turning around. The observations indicate that ants utilize visual cues in their surroundings when walking backward. According to Schwarz, they tend to take in information from the sides and behind when moving away from the nest, and then use it to guide their way back.