Australian Moths Are the First Known Insects to Navigate by the Stars, Revealing a Migratory Superpower
Bogong moths use both Earth’s magnetic field and the starry night sky to make twice-yearly migrations spanning hundreds of miles, according to new research
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Every spring, billions of nondescript moths hatch in southeast Australia. Not long after, the brown insects—called Bogong moths (Agrotis infusa)—take to the skies, flying more than 600 miles to the Australian Alps to escape the summer heat. Once there, they line the walls of cool caves and enter estivation, a summer dormant phase similar to winter’s hibernation. In the fall, they make the return journey to mate and die.
Biologists have long wondered how the nocturnal moths know where to go—especially since each new generation is making the journey for the first time. Past research has suggested they rely on Earth’s magnetic field, but scientists suspected something else might also be at play.
Now, a team of researchers says they’ve solved the mystery. Bogong moths use the starry night sky like a compass while making their twice-yearly migrations, according to a new paper published last week in the journal Nature. The moths are thought to be the first invertebrates to use the stars for navigation.
Fun fact: Bogong moth migration
Weather forecasters at Sydney’s 2000 Summer Olympics thought they saw an ominous storm cloud, then realized it was actually a swarm of millions of Bogong moths drawn to the stadium lights.
“Their parents have been dead for three months, so nobody’s shown them where to go,” says study co-author Eric Warrant, a biologist at Sweden’s Lund University, to CNN’s Jacopo Prisco. “They just emerge from the soil in spring in some far-flung area of southeastern Australia, and they just simply know where to go. It’s totally amazing.”
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For the study, researchers captured about 400 wild Bogong moths and brought them back to a lab. Working with one moth at a time, they glued the creature’s back to a thin rod and placed it inside a small, enclosed “flight arena,” the researchers write in the paper. The moths were still able to flap their wings freely and turn in different directions.
The scientists then created a magnetic vacuum to remove the magnetic field inside the arena, hoping to isolate any other senses that might be aiding in navigation. They projected the night sky at the top of the arena, like stars on the ceiling of a planetarium, then watched to see how the moths reacted.
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Without the help of an internal magnetic compass, the moths used the stars to orient themselves. Whenever the researchers rotated the image of the sky, the moths would turn to follow. When the scientists showed a random pattern of stars, however, the bugs became disoriented. “That was, for us, like the final proof, more or less, that they actually indeed use the stars for navigation,” says lead author David Dreyer, also a biologist at Lund University, to NBC News’ Evan Bush.
In another experiment, the researchers inserted small electrodes into the moths’ brains and saw that visual neurons lit up when they rotated the stars in specific directions.
Taken together, the findings suggest Bogong moths use stellar cues, in addition to Earth’s magnetic field, to migrate at night twice each year.
“That an insect brain that is smaller than a grain of rice is able to do this is just remarkable,” says Basil el Jundi, a biologist at Germany’s University of Oldenburg who was not involved with the research, to the New York Times’ Alexa Robles-Gil. “We’ve always thought, ‘Oh, they are just simple animals, they just fly toward lights and these kind of things.’ … But the brain network and the ability of these animals to perform quite extraordinary and complex navigational tasks is just mind-blowing.”
Moths have small eyes with tiny pupils, so they’re probably only able to see a few of the brightest stars in the night sky. The team suspects the insects are reliant on the Milky Way, which probably appears brighter to moth eyes than it does to human eyes.
If it happens to be cloudy one night, the moths probably lean more heavily on their magnetic compass to ensure they’re heading in the right direction. Having two navigational systems is an adaptation that likely helps the moths survive.
“If one fails, they have a backup system,” Pauline Fleischmann, a biologist at the University of Oldenburg who was not involved with the study, says to NPR’s Ari Daniel.
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Once they get close to the alpine caves each summer, the moths likely switch to yet another sense: smell. The caves produce a distinctive odor that smells a bit like rotting meat, reports NBC News. Once they catch a whiff, the moths know they’ve finally made it.
Having a better understanding of how Bogong moths navigate could be key to their conservation. Limiting light pollution, for example, might help prevent them from getting stuck in cities, per NBC News.
The species’ numbers have been plummeting in recent years: Because of severe drought and extreme heat that hit southeastern Australia between 2017 and 2019, the moth’s population dropped by 99.5 percent. Pesticides, fires, habitat destruction and climate change could have also played a role. The International Union for Conservation of Nature has listed the species as endangered since 2021.
“[Insect] numbers are all declining across time,” says Marissa Parrott, a senior conservation biologist at Zoos Victoria, to Yahoo News’ Michael Dahlstrom. “But then you get those big events like a major drought, flood or bushfires and they can wipe out entire species. We’re seeing that every day, that these animals are struggling. … We really need to change.”
