Bogong moth swarms signal potential recovery of endangered species

Over the past few days, New South Wales residents have noticed something unusual darkening their evening skies and gathering on their walls: swarms of bogong moths, insects about the size of a fifty-cent coin, arriving in numbers that have left researchers elated and scrambling to document what may be the first real sign of recovery for a species that nearly vanished entirely.

Hundreds of sightings flooded in over the weekend to Bogong Watch, a citizen science platform run by Invertebrates Australia, with reports coming from coastal areas across the state. One volunteer sentinel—part of a network of observers positioned around Mount Kosciuszko using non-lethal bug lanterns to track the insects—recorded more than two hundred moths in a single night. Three separate households each reported dozens more. The surge is part of the moths' annual spring migration, when they travel up to a thousand kilometers inland to cool caves in the Australian Alps, where they shelter through the summer heat.

What makes this year extraordinary is the sheer volume. Marissa Parrott, a reproductive biologist at Zoos Victoria who manages the separate Moth Tracker citizen science program, described the influx as unprecedented. In September alone, her team received more bogong sightings than during the entire previous year. Sightings have been climbing steadily over the past two years, she said, but this season has exceeded all expectations. "We're absolutely thrilled with what we're seeing," Parrott said, noting that one team member was moved to tears by the news.

The recovery matters because bogong moths are far more than a curiosity. They are pollinators, moving between plants as they migrate, and they are the primary food source for the mountain pygmy possum, a critically endangered marsupial found only in the high country. The moths also carry cultural weight—they were once so numerous that they periodically swarmed into Parliament House in Canberra, and during the closing ceremony of the 2000 Sydney Olympics, a swarm drawn by stadium lights was so massive that weather forecasters initially mistook it for a rain cloud.

That abundance is a recent memory. An estimated four billion moths arrived in the Alps each year until the population collapsed catastrophically between 2017 and 2019, dropping by as much as ninety-nine and a half percent. The cause remains unclear, though researchers have pointed to drought, heat stress, and other environmental pressures. The species was listed as endangered by the International Union for the Conservation of Nature in 2021, though it is not yet formally protected under Australian federal conservation law.

The current surge appears linked to favorable conditions: wetter, cooler weather across southeastern Australia has created the kind of environment bogongs need to thrive. Linnea Emneby, the project manager for Bogong Watch, emphasized that the high numbers are concentrated in New South Wales and the Australian Capital Territory, while Victoria lags behind. The moths do not arrive all at once but in waves, taking days or weeks to complete their migration. They are also remarkable navigators—the only invertebrate known to use a star map as a compass—though some occasionally get blown off course, with sightings recorded as far as New Zealand.

Yet optimism is tempered by climate uncertainty. The strongest El Niño on record brought drier, hotter conditions to Australia, and Parrott expressed concern about what the next couple of years might bring. For now, she and other researchers are asking the public to help protect the moths during migration: turn off unnecessary outdoor lights, avoid using insecticides, and if moths enter a home, gently place them back outside. Each female can lay two thousand eggs, making every individual precious. The moths cause no damage, eat no clothes, and will leave on their own. What they do is pollinate gardens and, if numbers continue to climb, restore a species that once seemed lost.