This moth species may use the Milky Way as its guiding star

One kind of Australian moth looks to the stars on its voyage to a summertime refuge.

Stellar cues from the Milky Way’s bright band may help Bogong moths (Agrotis infusa) chart a path from the sizzling plains of southeastern Australia to cool caves in the country’s Snowy Mountains, researchers report June 18 in Nature. While people, some birds and possibly seals rely on the night sky to navigate, Bogong moths are the first known invertebrates to reach a destination they’ve never seen before with help from the stars.

In spring, mounting temperatures and dwindling food sources send the moths roughly 1,000 kilometers south toward the caves, says David Dreyer, a neurobiologist at the Lund University in Sweden. “When they arrive … they line up [on] the walls [and look] like the skin of a rattlesnake.” The moths lie dormant until the fall, when they return to the plains to mate and die.

Dreyer and colleagues previously reported that the moths use magnetic and visual signals to migrate. The visual landmarks involved were unclear, but “one of the most obvious and stable cues is the stars,” says Eric Warrant, a neurobiologist also at Lund University.

Dreyer, Warrant and colleagues captured Bogong moths along their migration routes and tethered them to sensors inside a circular arena that blocked Earth’s magnetic field. The team also projected a realistic image of the night sky as it appeared outside the lab. “We just simply put the moths in there and let them fly under the night sky to see where they went,” Warrant says.

Under springlike skies, the moths flew southward, as they would if flying to the caves. They flew northward when the skies mimicked fall. What’s more, the moths’ brain cells fired in response to shifts in the night sky, suggesting attunement to its orientation.

The Milky Way’s elongated band or possibly its bright Carina Nebula, where many massive stars are being born, could be the insects’ guiding light, although it remains unclear. For humans, the moth’s trip is akin to walking from New York City to Indianapolis using just the North Star as a compass, Dreyer says.

It’s incredible that an insect has the “capacity to interpret the stars and read the Earth’s magnetic field in order to pick a specific direction to fly in,” Warrant says. “That’s a pretty phenomenal feat of navigation for an animal that has a brain a tenth the volume of a grain of rice.”