When the sun sets, millions of nocturnal ants awaken ready to eat. Some species forage all night, traveling from nest to food source and back again, often following trails they mark with scent. Scientists assumed bull ants, which don’t rely primarily on scent navigation, had to wake up before dark and use the day’s last light to find their way to sustenance. But a new study of one bull ant species shows the insects continue to navigate when the sun goes down—using an innate lunar compass.
Just as diurnal ants follow the relatively steady movement of the sun, the bull ant species has adapted to the orbiting moon’s constant changes, according to research published in Current Biology. The ants use what the researchers call time compensation: they keep track of how much time has passed since they left the nest to gauge where the moon should be in the night sky, much like early human navigators used the North Star.
“It was an area where we didn’t really know what was going on” until now, says lead study author Cody Freas, an entomologist at University of Toulouse in France. “These ants use a lot of different cues at the same time, and that helps them in case one cue becomes unreliable.”
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The researchers captured the insects en route to their usual feeding areas and put a subset into darkened boxes that lacked any environmental cues about time passing. (They put others in transparent boxes.) After several hours the scientists released the ants in a new location and watched them try to find their way to food. When held in darkness for long enough that the moon moved significantly, the ants veered off course, suggesting its position was their main cue.
“This is just a little bonkers,” says Rodolfo da Silva Probst, an entomologist at the University of California, Davis, who was not involved in the study. “They need to compensate for the trajectory of the moon. I mean, I don’t know how to do that.”
Other nocturnal creatures, including sand hoppers and moths, are thought to use the moon’s position to find their way, but these bull ants are the first found to have such an intricate, time-linked approach to lunar navigation. Additionally, researchers learned that the ants combine their impressive lunar compass with terrestrial and solar cues, at dawn and dusk, to navigate consistently even as moon visibility varies during the lunar month.
There are more than 12,000 ant species in the world, and they all do things a little differently, but figuring out how one species has adapted to its unique ecological niche might help researchers understand others, da Silva Probst says. “Maybe by studying other nocturnal ants, you might discover other mechanisms.”
