Bogong moth researcher Connor Marsland emerges from one of the mountain caves he monitors. Photo: Connor Marsland.
As thousands of bogong moths coated walls, windows and eaves across NSW, startling residents and setting social media alight, Connor Marsland was scaling the Brindabella Range to see how many had made it through.
The Western Sydney University PhD student was waiting at the other end of one of Australia’s great migrations, scrambling from peak to peak to check the cool mountain shelters where the moths spend summer.
Although Connor missed the first arrivals, the party in the mountains was just hitting its stride, the numbers still pouring in, surprising even him.
“Definitely more moths than I have ever seen up here over my last two years of monitoring these sites,” he said.
The annual migration has been unusually visible this spring, with swarms reported from northern NSW through Sydney, Canberra and the South Coast.
About the size of a bottle cap, bogong moths travel by night from breeding grounds across southern Queensland, inland NSW, western Victoria and parts of South Australia towards the Australian Alps.
With favourable winds, they can cover several hundred kilometres in a single night before sheltering from daylight, heat and predators in dark crevices.
Their complete journey can exceed 1000 kilometres.
Research published in Nature found they navigate using celestial cues, including the Milky Way, supported by the Earth’s magnetic field – making them the first invertebrate known to travel long distances this way.
Zoos Victoria senior conservation biologist Dr Marissa Parrott said its Moth Tracker project received more reports in one month this season than during its previous record year.
Researchers believe increased rain may have produced more food for bogong moth larvae, while warmer weather may have brought forward the flowering of plants that feed the adults.
But, they say, it’s too early to attribute the surge to any single factor and suggest what people are seeing may also represent a return towards the scale of migration once considered normal.
That prospect is significant for a species whose numbers crashed by an estimated 99.5 per cent between 2017 and 2019 and which was listed as endangered on the International Union for Conservation of Nature Red List in 2021.
Once in the Alps, the moths spend summer sheltering in cool caves and rocky crevices in a dormant state known as aestivation.
For Connor, being in the mountains as the moths settled into their summer refuges went to the heart of his PhD.
“Been a bit frantic at the moment; I think I’ve climbed six mountains in the last five days!” Connor said last week.
His project, which began in 2024, examines their migratory flyways and behaviour at aestivation sites – or, as his research laboratory puts it, what bogong moths do in the mountains and how they get there.
This season exceeded even Connor’s expectations.
The boom is encouraging given the concern about the species, but he cautioned against interpreting one abundant migration as proof its future was secure.
“This is not the norm, and we are still concerned about the impacts of extreme weather or drought on the bogong moth populations in future years,” he said.
Connor came to the project after completing a master’s degree examining whether spots and stripes in warning patterns protect insects from predators.
His fascination with bogong moths took hold when he realised they weren’t what he’d always imagined.
“I had grown up thinking that the bogong moth was something completely different from what it is, and finding out I was wrong about it just made me more curious,” he said.
Then he witnessed thousands of moths emerge from their caves and swirl through the air at sunset.
“From the first time I saw their maelstrom, I was hooked,” he said.
Despite the extraordinary scale of their migration, the routes bogong moths follow and their principal breeding grounds remain largely unknown mostly because their underground caterpillars closely resemble those of other moth species, making the places where they emerge difficult to identify.
Connor said finding those areas could reveal where conservation work was most needed as drought, floods and other climatic pressures intensified.
He was already in the thick of efforts to solve the mystery in February, when he joined scientists and volunteers for a 10-day tag-a-thon at Mount Kosciuszko.
The team marked about 14,700 moths with tiny paper tags or non-toxic white paint and returned them to their caves before their autumn migration.
Each recapture could have drawn a direct line between Mount Kosciuszko and another location.
Not one was found.
“Hasn’t fazed me at all!” Connor said. “It was always going to be a tough ask to locate a tagged moth when there are over four billion bogong moths flying around in total, but we have learned a lot from this experience and can only improve the project from here.
“What’s important is that we keep trying.”
But the search produced a much larger body of observations thanks to 50 volunteer “bogong sentinels” who were recruited to operate specialised lanterns around Mount Kosciuszko from March to May.
Some continued beyond the official monitoring period, giving researchers about five months of records and more than 2000 individual observations.
Connor said the lantern records had revealed striking shifts in abundance, including large numbers of moths observed in March and May.
Although too early to identify their migration routes, the observations were beginning to show where moths were likely to occur at different times of the year and would help guide future monitoring.
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Connor is also using cameras to record their arrival, departure and activity at summer sites across eastern Australia.
He isn’t simply studying the moths – during fieldwork, he lives among them.
“Simply put, it’s amazing,” he said. “There’s something magical about watching thousands of moths scatter across the skies at sunset, and seeing so many packed so tightly into such small spaces within the caves.”
The work is becoming more urgent as alpine temperatures rise.
He said the moths would probably seek shelter further up the mountains, but suitable habitat became increasingly limited towards the summits.
“Eventually, even the sites at higher elevations will become too warm and there will be little shelter left for the bogong moths over summer,” he said.
Bogong Watch will distribute another 100 bug lanterns across a wider area this season and is seeking volunteers within 250 kilometres of Canberra.
Project manager Linnea Vilhelmsson Emneby said finding 100 new lantern keepers was a significant task and wanted the expression of interest to reach as many people as possible.
Researchers are also investigating faster marking methods so they can tag more moths and improve the likelihood of a recapture.
“Just finding one moth would give us a direct pathway that that moth has travelled, from the point the moth was tagged to the point of recapture,” Connor said.
People interested in becoming a Bogong Lantern Sentinel can complete the online expression of interest form.
Original Article published by Edwina Mason on About Regional.
