Australia’s bogong moths are guided by the stars as they navigate up to 1,000km to a place they’ve never been before, new research has concluded, making them the first invertebrates confirmed to use celestial navigation.
Each year in spring, bogong moths emerge from their breeding grounds in the country’s south-east and migrate to the mountainous caves and rocky crevices of the Australian Alps to escape the summer heat.
In autumn, they return to their breeding grounds to reproduce and die.
But how do the moths know what direction to fly? And how do they know when they’ve arrived at their destination?
These questions have for decades bugged Prof Eric Warrant, who researches nocturnal vision in insects at Lund University.
“Nobody’s shown them [the way], their parents have been dead for three months,” he said.
“How the heck do they find this specific place that they’ve never been to before?”
Scientists in the 60s and 70s had already established that nocturnal migratory birds relied on stars and the Earth’s magnetic field as compasses. They suspected bogong moths might do something similar.
So, about 15 years ago, Warrant – along with an international team of researchers – set about trying to find out.
On land in the Snowy Mountains, researchers built a flight simulator for moths – roughly 50cm wide and lined with black felt – where the night sky was projected above them like a small planetarium.
Moths – captured mid-migration – were gently tethered at the centre, where they continued to “fly like mad”, Warrant said, but still manoeuvre and change direction.
Earlier research had revealed the Earth’s magnetic field played a role in steering flight, so a device called a Helmholz coil was used to cancel out magnetic fields, leaving only visual cues – the stars – to navigate by.
In experiments, conducted across two springs and two autumns, researchers manipulated the direction of the night sky – recreating it realistically, then turning it 180 degrees.
Consistently, the moths adjusted their bearings in order to fly in seasonally appropriate directions based on the stars, even when the sky was rotated.
When the stars were scrambled – without the Milky Way or the constellations – the moths became completely disoriented, Warrant said. They kept on flying, but went in all sorts of directions.
In a separate experiment, researchers inserted an electrode into the moth’s brain, and recorded neurological responses as they rotated the sky.
Brain regions dedicated to processing visual information and for navigation and steering fired strongly in response to these changes in orientation, particularly when moths were facing southwards.
Their findings, published in Nature, demonstrate that bogong moths rely on stellar cues, as well as the Earth’s magnetic field, as compasses to guide their long-distance journey.
“This is a truly remarkable insect,” Warrant said. “It can make this incredible journey with a tiny brain and a small nervous system, and do it in two directions.”
“People still think of insects as little automatons,” said Dr Kate Umbers, an associate professor in zoology at Western Sydney University and the managing director of Invertebrates Australia.
“They’re much more sophisticated little critters than we usually give them credit for.”
Umbers, who was not involved in the study, said the findings provided “a great weight of evidence” towards bogong moths having directional flight during their migration, as opposed to being blown around by prevailing winds.
Bogong moth populations have plummeted in recent years, but fundamental knowledge gaps and uncertainties have prevented the species from being listed under federal environment laws.
Learning more about the moth’s biology would help in designing conservation actions, Umbers said, and members of the public could help by sharing their bogong moth memories with Bogong Storytellers.
She said the Nature paper provided “another example of a little insect that’s doing something cool and amazing”.
“We should allow ourselves to feel the wonder of it, because it helps to remind us to care and to look after nature.”
