In the summer, the walls of the caves in the Australian Alps are tiled with Bogong moths.
Months before, billions of these small, nocturnal insects migrate about 600 miles to this destination — a place they have never visited before. Seeking refuge from the summer heat, they travel across southeast Australia to these cool alpine caves. Then, in the fall, they migrate back to their breeding grounds, where they eventually die.
This remarkable journey has long puzzled scientists like Eric Warrant, a neurobiologist at Lund University in Sweden. “How on earth do these moths know where to go?” he said.
Now, a study in the journal Nature by Dr. Warrant and his colleagues reveals the details of the insect’s impressive feat, showing that the Bogong moth may be the first invertebrate to use the starry night sky for migration. The findings suggest the insects use a set of internal compasses, one guided by the Earth’s magnetic field and the other by the night sky, to reach their destination.
“That an insect brain that is smaller than a grain of rice is able to do this is just remarkable,” said Basil el Jundi, a neuroscientist at the University of Oldenburg in Germany who was not involved in the study.
The Australian Bogong moth could fit in the palm of your hand. It has a two-inch-long wingspan, a small set of eyes and a brain that is roughly a tenth of the volume of a grain of rice. Despite their small size, they have played a big role in Australia. Once an important source of food for Indigenous Australians, the insect also holds a strong cultural value because of its impressive migration.
Few insects undertake long-distance migration from dispersed breeding grounds to meet in a single, specific destination. The most famous example is the monarch butterfly, which relies on the sun as a visual compass. Like monarchs, Bogong moths use the Earth’s magnetic field for their long journey. They combine the magnetic compass with visual cues or markers, though researchers did not know what these were.
To study which visual markers these creatures were using to migrate, the team created a flight simulator for captured moths. But catching these insects was no easy feat. After a series of droughts and wildfires spread across Australia from 2017 to 2020, Bogong moth populations collapsed by 99.5 percent, according to researchers.
Before the droughts, the cave walls could hold millions of moths. After, the caves were essentially devoid of them. “It was terrible,” Dr. Warrant said.
The droughts eventually broke with the destructive wildfires that scorched Australia in 2020.
Toward the end of the droughts, the team caught enough moths to conduct its experiments. The researchers placed the insects inside a lab-controlled simulator to test their behavior. They created a type of magnetic vacuum, stripping away the magnetic field inside the simulator. This allowed them to isolate the two compass systems and study only the visual one. The creature was tethered in the simulator, and the team projected the night sky on top, like a planetarium.
They found that, in the absence of the magnetic compass, the stars and the Milky Way were enough for the moth to orient itself in its migratory flight. If the researchers turned the projected sky 180 degrees, the moth would also turn.
“That was a huge surprise,” Dr. Warrant said. “They could actually interpret the stars to find a geographic direction.”
To fully understand the navigation system, the team also studied the visual neurons in the moth’s brain, to confirm if the neural responses matched the behavior.
In the experiment, the team inserted tiny electrodes into the insect’s brain. By doing so, they measured the neurons’ response to the same starry sky that provoked the behavioral response. As in the first experiment, the moth’s neurons responded to the sky’s rotation.
“The behavior and the neurobiology are hand in hand,” said Roy Riztmann, a biologist at Case Western Reserve University in Ohio who was not involved in the study. “Whenever you see a paper that does both of those things, that’s a really cool thing.”
The two different compasses might be helpful when conditions favor one over the other, Dr. Ritzmann said. For example, if there are cloudy skies or if the insect’s magnetic compass is knocked out, “having two maps is probably better than having one map,” he added.
Dr. Warrant said the study was born out of “utter curiosity and awe” and opened up new avenues of research. How do the magnetic and night sky compasses work together? Is one more dominant than the other? Once the moths arrive in the mountains, are there other cues that lead them to the caves?
“We’ve always thought, ‘Oh, they are just simple animals, they just fly toward lights and these kind of things,’” Dr. el Jundi said. “But the brain network and the ability of these animals to perform quite extraordinary and complex navigational tasks is just mind-blowing.”
Alexa Robles-Gil is a science reporter and a member of the 2025-26 Times Fellowship class, a program for journalists early in their careers.
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