On moonless spring nights in Australia, a billion tiny voyagers take to the sky. They lift from the parched lowlands, propelled not by instinct alone, but rather most remarkably by a map written in starlit sky. They are Bogong moths, soft-winged and brown, no bigger than a thumb. And now, scientists have discovered that these invertebrates are doing something once thought exclusive to birds, seals, and stargazing humans: they are navigating by the stars.
The new study reveals that Bogong moths use stellar cues to chart their long-distance migration across southeastern Australia. The discovery marks the first confirmed case of an invertebrate using a true stellar compass to determine direction.
“To our knowledge, this is the first time that a study demonstrated that an invertebrate can use nightly celestial cues to perform a long-distance navigation,” Dr. David Dreyer, a research engineer at the Lund Laser Centre and co-author of the study, told ZME Science. “This star compass might be used in conjunction with a magnetic compass.”
Nature’s Smallest Astronomers
Every spring, billions of Bogong moths (Agrotis infusa) emerge from the plains of southeastern Australia and fly up to 1,000 kilometers to the alpine caves of the Snowy Mountains in southern New South Wales. There, in dark caverns chilled by elevation, they aestivate—an insect form of hibernation—clinging to rocks in numbers so dense, their bodies blanket the walls.
Come autumn, the same individuals awaken and make the journey home to breed and die. This extraordinary round-trip migration—executed by moths that have never seen their destination before—has always proved puzzling.
Previous research showed that Bogong moths can detect the Earth’s magnetic field and likely use it to orient themselves. But magnetic fields, while useful, are vulnerable to distortion. Scientists suspected the moths relied on something else to stay on course.
“If you go to the Australian bush, where these moths live, and look around you at night, one of the most obvious visual landmarks is the Milky Way,” Dreyer said. “It’s always visible to some extent, independent of time of night and season.”
Now, they have found that in the absence of a magnetic signal, Bogong moths can still navigate accurately—as long as they can see the stars.
The Planetarium Experiment and a Compass in the Brain
The discovery emerged from a high-tech version of a celestial thought experiment. In a custom-built, magnetically shielded lab in rural New South Wales, researchers tethered Bogong moths inside a flight simulator that mimicked the experience of flying under a natural night sky. The setup blocked Earth’s magnetic field but projected real star maps onto a dome above the moths.
When exposed to a natural austral sky, moths flew in the direction consistent with their seasonal migration—southward in spring, northward in autumn. When researchers rotated the sky projection by 180 degrees, the moths flipped their orientation. And when the stars were scrambled into a meaningless scatter, the moths became disoriented.
This shows unequivocally that the starry sky alone is sufficient to guide them, the authors found.
The most surprising revelation though came from inside the moth’s head. Using fine electrodes, Dr. Andrea Adden from The Francis Crick Institute in London and colleagues recorded activity in neurons from three brain regions involved in navigation.
“We conducted electrophysiological intracellular recordings using sharp glass electrodes from 28 neurons,” Dreyer explained. These neurons came from brain regions responsible for vision and navigation, including the optic lobes and central complex.
Neurons responded specifically to the orientation of the starry sky. Many of them fired maximally when the moth faced south—its migratory heading in spring.
The neural activity formed distinct patterns depending on how the star map was rotated. Some neurons were excited when the sky turned in a particular direction; others were inhibited or showed bimodal peaks. These responses weren’t triggered by simple light or motion—they were tuned to features of the actual sky.
When scientists tested artificial visual cues mimicking parts of the Milky Way—like a bright dot or a bar-shaped stripe—many of the same neurons responded. This suggests that moths may key into both the brightest part of the Milky Way (such as the Carina Nebula) and its overall shape.
“The most exciting aspect of this is truly the scale of migration,” Dreyer added. “That tiny insect with a wingspan of 5 cm manages to fly about 1,000 km at night-time, potentially just by using the stars to steer the course still amazes me.”
Two Compasses, One Destination
Remarkably, the moths remain oriented even under cloudy skies, when stars and moon are hidden. In those cases, they appear to switch to their magnetic compass.
On clear nights, though, it seems the insects can rely entirely on the sky.
The dual system mirrors what has been observed in birds like warblers and thrushes, which also combine geomagnetic and stellar cues. It’s a safeguard against the unpredictability of nature: if clouds blot out the stars, magnetism takes over; if a magnetic storm disrupts the field, the stars provide a backup.
Previously, scientists found that the humble dung beetle also uses stars, but in a lesser role to orientate itself and roll its dung ball in a straight line.
“The reason we think Bogong moths use the stars to navigate is twofold: first, they are going towards a specific goal – the alpine caves in which they spend the summer – and second, they have to cross vast distances to get there. Dung beetles don’t care where they end up with their dung ball, they roll their ball in a random direction away from competitors on the dung heap. Bogong moths very much care where they end up, because if they don’t make it to the caves, they will likely die. Also, dung beetles only need to get far enough from the dung heap to eat their meal in peace, a distance they travel in about 10 minutes, while the moths are travelling almost 1000 km over many nights to a place they cannot see from where they start out,” said Adden.
For now, Bogong moths are the first known invertebrates to navigate using a true stellar map. But their future is uncertain.
Once abundant, their numbers have plummeted in recent years, prompting Australia to classify them as endangered in 2021. Climate change, drought, and habitat loss are thought to be driving the decline. Light pollution, while still relatively low across most of Australia, poses a growing risk.
“There is evidence for at least a temporary distraction of the Bogongs,” Dreyer said. “They pass several major cities, such as Canberra. In fact, a cloud of moths briefly took over the Australian Parliament by invading the actual parliament-room, which was evacuated as a result.”
The stars may guide them, but it’s up to us to ensure they still have a sky to follow.
Still, many questions remain unanswered. What specific celestial features do the moths track? Can they see individual stars with their compound eyes, or do they follow broader patterns like the Milky Way’s arc? And how does a moth brain—so small it fits on a pinhead—manage to integrate all this information?
The findings appeared in the journal Nature.
