Moths read the stars to complete an epic migration

For countless generations, every spring night in Australia has carried the faint whisper of wings. Billions of Bogong moths rise from the dry inland plains. Their destination is a handful of icy caves high in the Snowy Mountains, up to 600 miles away.

How these brief-lived insects – each one making the journey only once – find their way across such vast, feature-poor landscapes has long been one of biology’s quiet mysteries.

Now, an international research team has discovered the key: Bogong moths navigate by reading the constellations and the Milky Way, switching to Earth’s magnetic field when clouds blot out the stars.

The findings make the species the first known invertebrate to use a stellar compass for long-distance migration.

An unseen nightly moth migration

Bogong moths (Agrotis infusa) hatch on parched farmland and grasslands across southeastern Australia. Triggered by spring warmth, each insect embarks on a marathon flight toward cool alpine refuges.

When they arrive – sometimes only weeks after leaving birth sites – they wedge themselves into narrow rock cracks. There, they lower their body temperature and remain torpid through the scorching summer months.

Come autumn, they reverse course, return to the lowlands, breed once and die, leaving offspring to repeat the cycle.

Although the migration is centuries old, its navigational underpinning has been elusive. Earlier work hinted that moths might sense Earth’s magnetic field. But that alone seemed too crude to guide them to specific caves occupying only a few square miles in the vast Australian Alps.

The new study shows the insects wield a two-part navigation toolkit every bit as sophisticated as that of migratory birds.

Moths use celestial landmarks

Led by Professor Eric Warrant of Lund University, the research team built a custom flight simulator: a circular arena whose inner surface could project a perfectly realistic night sky, complete with Zodiac constellations and the luminous smear of the Milky Way.

By rotating or scrambling the projection, the team could test what cues the moths use. They also enclosed the device in coils that canceled Earth’s magnetic field, allowing independent manipulation of magnetic and visual information.

When moths collected during spring migrations were placed in the simulator under a natural star map, they reliably flew south-southeast – the direction to the Snowy Mountains from their capture location.

Autumn migrants, tested months later, flew north-northwest toward their breeding grounds. Rotating the star map 180 degrees caused the insects instantly to flip their direction of flight.

Scrambling the star pattern left them disoriented, proving they were not just chasing the brightest point but reading specific celestial landmarks.

Moths have a backup migration plan

Night skies are not always clear. The researchers next obscured the stars while reintroducing a controlled magnetic field.

Deprived of visual cues, the moths still flew along the correct migratory bearing, guided only by magnetism. When both stars and magnetic information were eliminated, the moths lost orientation entirely.

The results reveal a dual-compass strategy: starlight when available, magnetism when not. Such redundancy ensures reliability amid Australia’s famously changeable spring weather.

Brains tuned to stars

The team also ventured inside the moth’s brain. Using microelectrodes thinner than a human hair, they recorded from neurons in the central complex – an insect brain hub for spatial processing.

Certain neurons fired maximally when the simulated starry sky aligned with the migratory heading. Rotating the sky shifted each cell’s peak activity by an equivalent angle, confirming that these neurons encode celestial direction.

That sophisticated computation, packed into a brain weighing a fraction of a gram, rivals the navigational circuitry found in far larger animals.

From moths to machines

The discovery joins earlier breakthroughs revealing that South African dung beetles use the Milky Way to roll dung balls in straight lines.

Study co-author Javaan Chahl, a remote-sensing engineer at the University of South Australia, has already translated beetle astronomy into an AI sensor that allows robots to orient in low light.

He believes Bogong moths could inspire next-generation drones capable of navigating long distances at night without GPS.

Moth migration needs dark skies

Bogong moth numbers have crashed due to drought, pesticides, land use changes, and climate-driven shifts in vegetation. The species is now listed as vulnerable.

Light pollution compounds the threat by washing out the night-sky cues the moths rely on. Losing dark skies could push the migratory system past a point of no return.

This would trigger ripple effects across alpine ecosystems that rely on the moths as a seasonal food bonanza for birds and mammals.

“This is not just about a moth,” said Warrant, who also holds appointments at the Australian National University and the University of South Australia.

The findings help recognize that the night sky is a public commons, critical for countless species – humans included – that have used it to orient, to tell time, to wonder.

Navigation by starlight

For millennia, Polynesian navigators steered canoes by starlight, and mariners followed the Southern Cross across oceans.

Now we know that a creature no larger than a paper clip can do the same, threading a path across an entire continent by reading the celestial vault.

Safeguarding the Bogong moth’s migration means protecting the dark, starlit corridors overhead – an essential step if we are to keep both the insect’s ancient journey and our shared cosmic heritage alive.

The study is published in the journal Nature.

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