A 1,000-kilometer nocturnal flight
Each spring, billions of Bogong moths (Agrotis infusa) emerge from the soil across the plains of southern Queensland and western New South Wales. These newly adult moths then embark on a nocturnal migration of up to 1,000 kilometers to the Australian Alps. Their destination is a specific set of cool, high-altitude caves and rock crevices, typically above 1,500 meters, where they will escape the summer heat. This summer dormancy, known as aestivation, can last for up to four months.
Inside these alpine caves, the moths settle in astonishing densities, reaching up to 17,000 individuals per square meter. They live off the fat reserves they accumulated as larvae, which can constitute about 60% of their dry body weight. At the end of summer, the very same moths that arrived months earlier undertake the long journey back to the inland plains where they were born. Upon their return, they mate, lay up to 2,000 eggs each, and then die, beginning the cycle anew.
An internal compass
The Bogong moth's ability to navigate to specific caves, which they have never visited before, has long been a subject of scientific study. Research has confirmed that these insects possess a sophisticated dual-compass system. One of their primary navigation aids is an internal magnetic compass. Experiments using flight simulators where the Earth's magnetic field was cancelled or reversed showed the moths' reliance on this sense for direction. It is believed that a light-sensitive protein in their eyes, called cryptochrome, may be responsible for allowing them to perceive the magnetic fields.
Besides magnetoreception, Bogong moths navigate by the stars. They are the first invertebrate species known to use celestial cues, such as the Milky Way and prominent constellations, for long-distance travel. When flight simulator experiments presented the moths with a rotated night sky, the moths altered their flight direction accordingly. The combination of the magnetic compass and stellar cues provides a robust navigation system, allowing them to maintain their course even on cloudy nights when stars are not visible.
a cultural and ecological center
For thousands of years, the annual moth migration was an event for Aboriginal peoples of southeastern Australia. Groups would travel to the high country to harvest the moths, which were a source of fat and protein. Archaeological evidence from Cloggs Cave in Victoria shows that a grindstone was used to process Bogong moths into a paste or cake around 2,000 years ago, confirming long-held oral traditions. The moths were typically roasted in hot ashes, which would singe off their wings and legs, and were said to have a nutty flavor.
The massive influx of moths is also an ecological event. The moths transport nutrients from the lowlands to the alpine ecosystem. They are an important food source for numerous alpine species, most notably the endangered mountain pygmy-possum (Burramys parvus). This small marsupial relies on the fat-rich moths to survive hibernation and raise its young. In recent years, severe droughts in the moths' breeding grounds have led to a dramatic decline in their population, impacting the entire alpine food web.