How a moth 'maelstrom' gave scientists hope for an endangered species

Kale Munro was exploring the 1,750-metre summit of Mount Wills, in Victoria's High Country, when ten or so bogong moths began to gather around dusk. 

It was a cool night, and as the Sun continued setting, the swarm started to grow. 

"I started seeing handfuls and thinking, wow, what a cool thing to witness," Mr Munro said. 

"But then as the sun started to drop and it got dark, these handfuls suddenly turned to hundreds."

By the time the sun set, Mr Munro was completely surrounded by thousands of moths. 

Mr Munro is a proud citizen scientist who has kept a close eye on the bogong moth over the years. 

Every spring, endangered bogong moths can migrate more than 1,000 kilometres as part of their annual migration to Australia's alpine zone. 

At the same time, the critically endangered mountain pygmy possums wake from their winter hibernation and head out for their preferred food source: the bogong moth. 

Bogong moth numbers have been declining since the 1980s and suffered population crashes in 2017 and 2019. So watching a "maelstrom" of moths descend on Victoria's alpine region was something of a treat for Mr Munro.

The next morning, he found several granite crevices at the summit completely "carpeted with nesting bogongs".

"I was really treated to this site of just thousands of moths tiling the walls," he said. "It was a pretty incredible experience."

The busy bogong

Each spring, bogong moths emerge from under the soil on their breeding grounds in Queensland, New South Wales and western Victoria and fly more than 1,000km to the alpine region.

The moths spend summer in mountain caves before returning to breed over winter. Their larvae then feed on plant roots underground.

Zoos Victoria Population and Breeding Specialist, Dr Marissa Parrott, said the zoo's citizen science project, "Moth Tracker", which was launched in 2019, had logged more than 14,000 sightings this year.

"In our previous best year, it was around 2,000," Dr Parrott said. 

Dr Parrott said moth numbers may now be reaching a critical mass after recent wet seasons.

Significant population declines in 2017 and 2019 were attributed to severe droughts in lowland breeding and feeding grounds, which starved the larvae of vital nutrients from plants. 

But Dr Parrott said the moths remained endangered due to the warming alpine habitat and other factors, such as drought. 

Scientists do not fully know why the moths migrate to certain places, how they pick their alpine caves, or why they swirl together in groups called a maelstrom, as Mr Munro saw.

"[It] might be light, it might be heat, or they might need water because they have been seen drinking during these times," Dr Parrott said.

The recent population growth has given researchers hope for the survival of the mountain pygmy possum, which relies on the bogong moth as a preferred food source. 

In previous years, female possums were unable to raise their babies due to a lack of food. 

"In fact, across all Victorian monitored populations, more than 50 per cent of female mountain pygmy possums lost their full litters of babies," Dr Parrott said. 

"In the worst affected population, it was about 95 per cent of females losing their young."

Footage helping researchers

Mr Munro's footage caught the attention of Western Sydney University  (WSU) PhD student Connor Marsland, who has been studying bogong moths and their migration paths since 2024.

He uses citizen science submissions on websites like iNaturalist and Zoos Victoria's Moth Tracker. 

He said Mr Munro's submission from the top of Mount Wills was spectacular. 

"It's just something magical about so many moths flying around at the same time," he said.

"You can't look anywhere without them being there when that happens."

Mr Marsland said citizen science submissions help researchers locate moth caves and learn more about their summer dormancy, a process called aestivation.

"There's only so many sites that we can get to over this time," he said. "So, with people going out into the field and finding these kind of locations for themselves, if they let us know, then we're able to use this information to find the best locations to monitor in future years."

WSU entomologist Dr Eleanor Drinkwater said researchers appreciated the role of the public. 

"I did the maths the other day, and I worked out that [those] who are volunteering their time to monitor these insects for us have collected the equivalent of 12 years' worth of nights … in under a year," she said.

"Which is just amazing."