Common name Bogong moth
Scientific name Agrotis infusa
Type Insect
Diet Adults eat nectar, larvae feed on plant seedling
Average lifespan The full life cycle takes one year to complete
Size Adult moth wingspan up to 5cm; larval caterpillars grow to a length of about 5cm

In one of the many great annual migrations of the natural world, these native Australian night-flying insects have been making the same journey across up to 1000km for millennia.

It’s an epic excursion for a tiny creature that takes the species from its winter breeding grounds in Queensland’s Darling Downs and the dry inland plains of NSW and Victoria to the Snowy Mountains and Bogong High Plains of the Australian Alps, and back again.

From late September onwards young moths arrive at the Alps where they enter caves and crevices, mostly above an elevation of about 1800m. Here they line rock walls in their hundreds of thousands – up to 17,000 per square metre – to survive the hot months in a form of summer hibernation known as estivation.

They arrive at the Alps in their billions, representing a huge influx of high-fat, high-protein insect food that’s critical to Alpine ecosystems and is devoured by a range of animals, particularly marsupials. This summertime Bogong moth bounty has also been harvested for thousands of years by Indigenous peoples who feasted on the insects after roasting them whole.

In late February–early March those moths that that have survived the summer set off at night to fly to their breeding grounds where they mate, lay eggs and die.

Each female lays up to 2000 eggs in the ground. These hatch after about five days and, eating plant stems at ground level, the resulting larva grow and fatten until they reach a length of about 5cm.

These caterpillars are regarded as pests of crop plants, and many are killed each year by pesticides applied by farmers. Those that survive pupate in the ground and emerge in early spring to begin their migration back to the Alps.

They fly by night and feed on nectar, building up fat reserves ahead of their summer estivation.

In 2021, the bogong moth was added to the IUCN’s red list of threatened species, identified as endangered following crashes in recent years in the species’ population due to: protracted drought brought about by climate change; light pollution, which often sees adult moths fatally diverted from their migrations; and pesticide use.

Related: Solving the bogong moth mystery