Australia's bogong moth — an endangered species that once migrated in the billions — is surging back in numbers that have startled residents across New South Wales. Reports to the Moth Tracker citizen science platform this September alone have already exceeded the total for all of 2025. Swarms have descended on Sydney and Canberra, blown cityward by strong winds that diverted typical inland migration routes. For an insect that suffered a catastrophic 99.5% population crash between 2017 and 2019, the comeback is striking. The collapse was driven by severe drought in the moths' breeding grounds across southern Queensland, NSW, the ACT, and into South Australia and western Victoria. The recovery, such as it is, owes itself to the inverse: wetter, cooler conditions this year that favoured breeding. An estimated 4 billion bogongs used to arrive in the Australian Alps annually to aestivate in cool caves during summer. Current population figures remain uncertain — Linnea Emneby of Invertebrates Australia's Bogong Watch project says only that "it does look like they're on their way to recovery." The moths are a keystone species in the alpine ecosystem. They navigate using the Milky Way — the only invertebrates known to use celestial navigation — and the Earth's magnetic field, flying up to 1,000 km on their first migration months after their parents have died, to caves they have never visited. Their fat-rich bodies fuel alpine food chains. The population crash rippled through the ecosystems that depend on them. What makes this recovery fragile is its dependence on weather rather than any structural change in land management, drought resilience, or habitat protection. Bogongs are a boom-and-bust species, but climate change has amplified the bust cycles with prolonged drought and bushfires in regions that historically didn't burn. As Emneby put it, their recent absence was "as far as we know, not normal." A return to drought conditions could erase this year's gains entirely. The citizen science infrastructure — Zoos Victoria's Moth Tracker and Invertebrates Australia's Bogong Watch on iNaturalist — represents genuine distributed monitoring capability. Dr Marissa Parrott of Zoos Victoria reports verified sightings from almost every state and territory except the Northern Territory. This is low-cost, high-coverage data collection that gives researchers real-time migration tracking without expensive sensor networks. Public response matters more than usual for an insect species. Experts are urging people to avoid insecticide, turn off unnecessary outdoor lights to reduce attraction, and gently relocate moths found indoors using the glass-and-paper method. "Every moth is precious," Parrott says. The species' recovery depends partly on millions of individual human decisions not to kill insects that land on their laundry or clog their vents. The deeper question is whether this is a genuine recovery or a single good year in an increasingly volatile climate. Historical records show bogongs once stopped trains and obscured lighthouse beams. The current surge, while promising, is being treated as remarkable rather than normal — a sign of how rapidly baseline expectations have shifted. Without structural climate adaptation, the moths remain one prolonged drought away from another crash.
