Every spring, millions of Bogong butterms hike from their breeding grounds in Southeastern Australia in cool caves in the Australian Alps. They cover hundreds of kilometers to a place where they were never before. But how do you find your way? A study now shows that the moths are not only based on the earth’s magnetic field, but also on the stars. Specialized neurons are responsible for this in the tiny brain of the insects. Which characteristics of the night sky serve the moths as a clue is still unclear.
In the Australian spring, millions of bogong butterms (agrotis infusa) make their life on the journey of their lives every year: shortly after they have slipped in their breeding grounds in the hot southeast of Australia, they fly up to 1000 kilometers to the Australian Alps. A small number of cool caves and crevices serve these night folds as a summer quarters. In autumn they return to their breeding grounds to multiply there and then die.
But how do the moths know in which direction they have to fly and when they have reached their goal, although each generation only takes the long journey once in their lives, so that no experienced individuals could show the way? Earlier experiments had already shown that the insects have a magnetic sense and that they can probably orient themselves on the earth’s magnetic field. However, this knowledge did not provide a complete explanation.
Starry sky as a compass
A team led by David Dreyer from the Lund University in Sweden has now proven that the Bogong butterms are also based on the stars. In addition, the researchers caught numerous Bogong butchers at the beginning of their hike in spring and autumn and put them in a specially designed flight simulator. In a kind of planetarium, this depicts the night sky and neutralizes the natural magnetic field of the earth.
Although the moths could not rely on their magnetic sense under these conditions, they flew reliably in the right direction when a natural night sky is overlooked – i.e. in spring to the north in autumn. “However, if we turned the projected night sky by 180 degrees, the animals flew exactly in the opposite direction,” reports the team. On the other hand, if the stars in the simulated night sky were randomly distributed, the moths did not show any preference for a certain direction, but flew around disoriented.
Sophisticated neural mechanisms
“This proves that the Bogong butchers don’t just fly to the brightest light or follow a simple visual indication,” says Dreyer’s colleague Eric Warrant. “You read certain patterns in the night sky to determine your geographical direction, just like migratory birds”. The Bogong butchers are therefore the first known invertebrate animals that rely on a star compass on their long-haul trip. They also take into account that the starry sky moves during the night and also looks different in different seasons.
In other experiments, Dreyer and his team revealed the neurological foundations of this complex behavior. Accordingly, specialized neurons in the brain of the moths react to the alignment in relation to the starry sky. These neurons fire the strongest when the animal is directed south – regardless of the season. “This type of directional vote shows that the brain of the Bogong Motte Himmelinformations encodes in a surprisingly sophisticated way,” says Warrant. “This is a remarkable example of complex navigation skills in a tiny insect brain.”
So far, it is still unclear to which stellar hints the moth rely on. It is questionable whether she can identify individual stars and constellations with her faceted eyes. Maybe the Milky Way, which can be seen as a bright light strip in the southern half of the sky, could help her with orientation. Earlier studies had already shown that dung beetles also use the Milky Way – but not for long -distance trips, but to roll their dung balls in a straight train.
Source: David Dreyer (University of Lund, Sweden) et al., Nature, DOI: 10.1038/S41586-025-09135-3
