Massive swarms of bogong moths once resembled rain clouds – then their numbers crashed to earth

The Guardian

08-04-2025

The bogong moth was once so abundant it was mistaken for weather. During Sydney's Olympic Games in 2000, a swarm of bogong moths attracted by stadium lights was so huge that meteorologists mistook it for a rain cloud.
But the species known as 'deberra' in Taungurung language – an insect with deep cultural and ecological importance, but which is smaller and lighter than a paperclip – has not returned to those numbers since the population collapsed by up to 99.5% in the two years before 2019.
In February the environment minister, Tanya Plibersek, decided against listing the species as threatened under federal conservation laws, citing gaps in data and uncertainties about the moth's population due to limited monitoring and its migratory nature. The bogong moth has been on the global endangered list compiled by the International Union for the Conservation of Nature since 2021.
Prof Brendan Wintle, a lead councillor at the Biodiversity Council and a conservation ecologist at the University of Melbourne, calls Plibersek's decision 'very disappointing' given that most experts agree the species is in trouble.
Every spring, bogong moths migrate hundreds of kilometres to escape the summer heat, travelling from low-lying breeding grounds in southern Queensland and western New South Wales and Victoria to mountainous caves and rocky crevices in the Australian Alps.
'They do that without ever having done that before,' Wintle says. 'It's quite unique for such a small animal to travel such a long distance.'
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While bogong moth numbers have improved, they remain well below levels recorded before the crash. Wintle says the shift from 'hyper abundant' to scarce could have catastrophic consequences for alpine ecosystems.
The species is under pressure from the climate crisis, he says, and from land clearing for farming. Bogong moths rely on cold temperatures at the top of mountains for a period of dormancy to complete their life cycle. But those places are rapidly warming.
The moths are widely known and recognised but scientists say there are 'fundamental knowledge gaps' about where they breed, how much their population has fluctuated and the threats they face. They are calling for significant funding to plug knowledge gaps and to work out how to protect the species.
The population decline has ecological and cultural implications. Bogong moths are a crucial food source for the mountain pygmy possum, a critically endangered species and Australia's only hibernating marsupial.
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Dr Marissa Parrott, a senior conservation biologist at Zoos Victoria, says the possums rely on the moths for important fats, proteins and nutrients after waking from five to seven months hibernating under snow. She says the species is critical to alpine ecosystems because its annual migration brings an influx of nutrients that nourished the soil, fungi, plants and animals.
The bogong moth also is culturally significant to many First Nations people, including the Taungurung people of central Victoria. Matt Shanks, executive manager of bio-cultural landscapes at Taungurung Land & Waters Council, says the high-elevation sites where the moths spend the summer were also important ceremonial and meeting places for Taungurung and other First Nations people. Deberra feature in Indigenous stories stretching back tens of thousands of years.
At the height of its population, the moths were recorded in every state and in the Australian Capital Territory. Wintle says this means saving the species will require nationwide coordination by governments, First Nations communities, land owners, researchers and citizen scientists – a project he says would be on a similar scale to that required to restore the Murray-Darling basin.
A genetic analysis published in the journal Biological Conservation found high levels of genetic diversity in moth populations, suggesting they arrive in the Alps from a variety of breeding sites then mix randomly.
Dr Collin Ahrens, a conservation geneticist and co-author of the paper, says it suggests site-specific conservation measures would be less useful than strategies that supported the species across its entire range, including work to understand and limit farming practices that could be contributing to its decline.
Parrott says there is significant public enthusiasm for bogong moths, demonstrated by members of the public reporting nearly 2,000 moth sightings to a Zoos Victoria citizen science platform, Moth Tracker, between September and December. About half of the sightings have been verified as bogong moths.
She says the data collected could improve understanding of the 'tiny but mighty' moths by tracking movements and population changes.
Dr Kate Umbers, an associate professor in zoology at Western Sydney University and the managing director of Invertebrates Australia, says the moths' Australia-wide distribution is 'great, in a way, because it means everybody can be part of looking after it'.
'They have the potential to get agricultural and conservation scientists working together to solve these 'grand challenges' of biodiversity conservation, around how we manage land effectively, to both feed people and look after nature,' she says.
But Umbers says it will be more challenging to fund and coordinate research and recovery efforts while the species is not recognised as threatened under federal law. In the short-term, she says the assessment process has identified areas in which more data is needed, and emphasised the need for the community to work together to protect the moth and its extraordinary migration.