It's an extraordinary journey.
After hatching in breeding grounds across south-eastern Australia, the bogong moth spreads its wings as the weather warms up.
The moths travel in their billions more than 1,000 kilometres to the coldest parts of the country: caves and crevices in the Australian Alps.
They manage to navigate this incredible distance despite being only about 2 to 3 centimetres in length.
"They weigh a third of a gram, which is less than a Tic Tac," says Marissa Parrott from Zoos Victoria.
"But they can migrate over 1,000km every year up to the alpine zone and then back again to their breeding grounds."
"It's an amazing lifestyle, especially because they've never been to this destination before," says bogong-moth expert Eric Warrant of Lund University.
"That's a little bit like me waking up in the morning here in southern Sweden and deciding to go to the South Pole," Professor Warrant says.
The moths stay in the mountains in a dormant state (aestivation) for months, providing important nutrients for local species including the critically endangered mountain pygmy possum.
But in recent years their numbers have been way down. Drought saw the population plummet by an estimated 99.5 per cent.
Now the rain keeps falling, their numbers are up — but it's not all good news.
In recent years, scientists have started new initiatives to track and better understand the plight of the bogong moth.
The crash
In a single year — 2017-18 — the bogong-moth population was close to wiped out, and last year they were added to the International Union for Conservation of Nature (IUCN)'s endangered list.
"It was the worst drought actually in our history — not only during European history but for a long time back in our geological history it seems as well," Professor Warrant says.
The moth's breeding areas in semi-arid regions dried out, harming the caterpillars and leaving them with little vegetation to feed upon.
This season, as the east coast experiences its third consecutive La Niña, Professor Warrant says the moth numbers are looking much better in places like Kosciuszko National Park (New South Wales), the Brindabella Ranges (the ACT), and Mount Buffalo (Victoria).
"We have got good science that the moths are returning in reasonable numbers to the mountains," he says.
But there is also such a thing as too much rain.
"The rain has been very problematic for many reasons, including in the breeding areas, there's been a lot of flooding as well, so it's not impossible that a lot of developing moths actually drowned this year.
"Sufficient areas were wet enough to create enough vegetation but not so wet as to drown the moths."
Moth monitoring
Zoos Victoria reproductive biologist Marissa Parrott has been monitoring moth sightings since 2019 through citizen scientist project Moth Tracker, set up after the population crash.
"Zoos Victoria launched Moth Tracker in response to the catastrophic decline of the beautiful bogong moths in 2017 and 2018," Dr Parrott says.
"It was a way that everybody could come together to help the species."
While this year is Moth Tracker's best since launching, including verified sightings in Western Australia and Tasmania for the first time, Dr Parrott says there are still grave concerns for the species.
"The numbers are still critically low and we still need to focus on how best to help them, to track them, and to support them on their migration.
"We know there are still key threats out there, things like changed agricultural practices and insecticides, predators, light pollution, and of course those more extreme droughts and even bushfires."
Another monitoring project has recently begun at Falls Creek in Victoria, where bogong moths were once a common sight in the ski village, according to accommodation owner Christine Irish.
"A few years ago we used to notice so many of them," she remembers.
"We'd go into rooms and we'd fill a vacuum cleaner with these moths, and you'd go in the next day and you'd vacuum them up again.
"But what I have noticed is over the last two or three years we're not seeing too many, and I'd really like to ask someone in the know: 'What's happened to the bogong moth?'"
Naomi Monk, an environmental officer at Falls Creek Alpine Resort, has been thinking about this question, and how to gather data on moth numbers to track them long-term.
Lights on the mountain
In 2019, as Zoos Victoria was setting up Moth Tracker, Ms Monk was sweeping butterfly nets through the air.
She was trialling methods to count the moths — which, she discovered, fly too high for butterfly nets.
After experimenting with light traps, and using a head torch to spot and manually count the moths, she came up with a prototype to track the moths remotely.
"It's an automated light-beam monitoring device. It's essentially a camera and a spotlight that are powered up together with a timer and it allows us to record the number of moths that are passing through the spotlight," she explained.
"When the moths pass in front of it, it's really neat to see — they almost look like little shooting stars, but with their unique flight pattern so you know it's the bogong moth passing in front of it, and they're quite easy to count that way."
This season has been delayed by prolonged snow cover, which, according to Professor Warrant, could mean the moths are still gathering in alpine caves into January.
He says it's too early to tell if moth numbers will be back to pre-drought levels this season. While the signs are promising, he's still "very worried" about the moths.
"Had you asked me just five or six years ago would it be ever possible for the bogong moth to become extinct I would have just laughed, simply because it's such a common, widespread and numerous animal.
"But … the recent drought proved to me how vulnerable even the most common and apparently resilient species is in the face of climate change."
Professor Warrant says what we're seeing, as the pendulum has swung from the drought of 2017 to the floods of 2022, is "extreme climate" in action.
"If we don't have a way of reversing these extreme weather events in the future, I don't see that we can actually honestly feel that the bogong moth is safe … I don't think we're out in the clear by any means."
