Ants visually track the motion of objects as they move through their environment in order to determine the distance they have traveled, a new study reports. Such tracking, called optic flow, has been observed in a number of insects but was thought to be used only minimally by ants. Now, results by Sarah Elisabeth Pfeffer and Matthias Wittlinger suggest that certain ants can rely solely on optic flow to find their way back to their nest when lost. Here, they studied Cataglyphis bicolor desert ants, which exhibit unique behaviors; namely, experienced forager ants carry interior nest workers, who are much less familiar with the outdoor environment, between different nest sites. Previously, studies revealed that Cataglyphis bicolor ants are able to calculate the distance they've traveled based on the number of steps they have taken, essentially relying on internal odometer mechanisms. To explore how these ants -- particularly those that are carried, and don't take steps -- may also use optical cues, the researchers connected two entrances of neighboring nests with a walking channel. Once a forager ant carried its nest mate ten meters in one direction, the two ants were separated. After an initial search around the release point, presumably to locate its absent foraging partner, the carried ant set out for the home nest, getting close to the nest position. By contrast, control ants that were "blindfolded" when they were separated and released were unable to locate the home nest, suggesting that optical cues are critical to gauging distance. Further experiments revealed that this optical flow measurement capability operated independently from ants' odometer mechanism, giving ants two unique systems for measuring distance.
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