Each year, the bogong moth (Agrotis infusa) takes an impressive migratory journey across the Australian landscape. As spring arrives, billions of these moths leave their breeding grounds and fly only at night. They cover distances of up to 1,000 kilometers (620 miles) to reach a new destination: the cool, hidden caves in the Australian Alps. There, they enter a dormant state called aestivation, which is a period of inactivity during the summer before dispersing in the autumn to breed. This process helps them continue their species and ensures the next generation instinctively returns to the summer caves.
Scientists have been fascinated by how these moths complete this remarkable journey, especially since their lifespan is only about a year, suggesting that this migratory path is instinctive. A significant breakthrough has recently provided clarity on this enduring mystery: these nocturnal travelers navigate by following the stars. Dr. Andrea Adden, a neuroscientist at the Francis Crick Institute in the UK, explained that their study showed bogong moths can use the starry sky to maintain their migratory direction without any other cues. This skill indicates their ability for celestial navigation. It allows them to fly accurately over long distances toward a specific migratory goal.
The flight of the bogong moth is an extraordinary sight; they soar for hours through the night, resting during the day in any available hiding spots. It’s common for entire towns to be covered in resting moths as they make their way to the Australian Alps, with the migration lasting several nights. Animals use various signals and cues for long-distance navigation. Some have special features to sense Earth’s magnetic field, while others depend on visual cues like the moon, the sun, or notable landmarks. Past research by zoologist Dr. David Dreyer and senior author Dr. Eric Warrant from Lund University suggested that bogong moths used a mix of magnetoreception and visual cues. However, it now seems that magnetism might not be as important as previously believed. To explore these earlier findings, Dreyer, Adden, Warrant, and their team ran a series of experiments to identify specific visual cues. They set up a Helmholtz coil system to eliminate Earth’s magnetic field and projected various starry views onto a vacuum chamber. They observed that the moths continued to fly in the appropriate seasonal direction. Further testing involved showing moths different images of the night sky while Dr. Adden recorded their brain activity using single-cell electrophysiology. Dr. Dreyer explained that a very thin glass electrode, finer than a human hair, was inserted into certain brain areas of a moth to reach the cell membrane of navigation-relevant neurons.
The electrical activity of these neurons was then amplified and recorded for later analysis. The researchers impaled the cell and exposed the moth to rotating images of the starry sky, along with various control images. They found that about 28 of the recorded neurons responded to changes in the orientation of the starry sky but not to the control image, which had a random arrangement of stars. This observed rotation is important and can be better understood by comparing it to another animal that uses stars for navigation: the dung beetle. Prior research has shown that dung beetles use a mental map of the stars to find their way home after rolling a dung ball away from a dung pile. However, their journey is quite different from that of the bogong moth. Dr. Adden noted that dung beetles do not focus on their final destination; they simply roll their ball away from competitors in a random direction. They only need to travel far enough from the dung heap to eat in peace, typically in about 10 minutes.
In contrast, the bogong moth’s journey is much longer. It can last several weeks, with sustained flight for hours at a time. The stakes are significantly greater. If a moth fails to reach its cave before summer, it has very low chances of surviving until the next breeding season. Dr. Dreyer emphasized the challenges, explaining that moths must adjust for crosswinds and, importantly, for the rotation of celestial bodies throughout the night if they mostly rely on their sky compass. The study suggests that if bogong moths keep a certain angle relative to a celestial cue, like the Carina Nebula or the long axis of the Milky Way, they would need to adjust this angle by steering to stay on a straight flight path. While the exact celestial cues the moths use for navigation are still unknown, the research clearly shows they can navigate under a starry sky even without a magnetic field. Dr. Warrant told ScienceAlert that their research focused on two main questions: how the bogong moth determines its migratory direction and how it knows when to stop. He mentioned they are now starting to explore the second question.
They aim to identify the sensory cues tied to their destination, which will be the next focus of their research. Another clear area for future investigation is understanding how the moth’s brain integrates magnetic and stellar information. Celestial navigation is relatively common in the animal kingdom, used by humans, some birds, seals, and frogs. Other moths and butterflies rely on the sun for navigation. Therefore, it is unlikely that the bogong moth is the only insect capable of navigating at night in this way. However, this does not lessen the wonder of their achievement. Dr. Dreyer expressed his ongoing amazement that a tiny insect with a wingspan of just 5 cm and a brain around one-tenth the size of a grain of rice can fly about 1,000 km at night, potentially using only the stars for direction. He likened it to walking that distance without food or shelter, solely during the night, and without the use of GPS or a compass. Even a small, five-degree error in direction on the first night would result in being 90 kilometers off after 1,000 kilometers. With multiple nights of travel, there is plenty of opportunity for navigation errors. The story, he concluded, remains compelling.
