Plate Nº 45 · recorded October 2, 2026
Biology & EvolutionReported finding
Bogong Moths Swarm Australia Again After Near-Collapse
Swarms dense enough to blot out the moon have returned to eastern Australia after drought and habitat loss wiped out 99.5 percent of the species — but scientists fear an El Niño summer.
By Marcus Bennett3 min read607 words
In brief
- Drought, pesticides and habitat destruction wiped out an estimated 99.5% of the bogong moth population after 2017.
- In a good year, 4 billion or more moths migrate to alpine caves in eastern Australia, where they cover cave walls in dense mats.
- Bogong moths are the first invertebrates shown to use the Milky Way for long-distance navigation.
Moth swarms so dense they can blot out the stars are fluttering across eastern Australia, marking the return of a migratory spectacle the country has not seen since the bogong moth nearly went extinct almost a decade ago.
For generations, the great bogong migration was a fixture of the Australian spring. Each year, billions of the insects hummed down the nation's east coast, fleeing the inland heat in search of cooler shelter. In a good year, 4 billion moths or more made the trip to the alpine caves of eastern Australia.
"So many bogong moths would come through that they could block out the stars and the moon as they went overhead," said Marissa Parrott, a conservation biologist at Zoos Victoria.
A collapse of 99.5 percent
That spectacle nearly ended for good. Drought, pesticides and habitat destruction triggered an unprecedented population crash that began in 2017. Within a few years, an estimated 99.5 percent of the bogong moth population had vanished.
The migration technically continued, but scientists were stunned by how few moths showed up. "People described going into the caves and finding barely any moths, and just kind of being in shock," said Eleanor Drinkwater, an insect researcher at Western Sydney University.
Now the bogongs are back, and researchers could not be happier. "There have been happy tears in my office because this is what nature should be," Parrott said. "People are noticing those big swarms again. They can celebrate what I think is one of nature's great spectacles."
Life in the caves
The moths' destination is a string of caves high in the mountains, where they spend the hot months in extraordinary density. Photographs have shown cave walls so densely covered that the rock beneath is invisible.
"They get up into the mountains and into these caves, where they make this beautiful tiling pattern," Drinkwater said. "They cover the walls in this very dense mat of moths. They hang out there until the weather starts getting cooler, and they come back down to their breeding grounds."
Each moth makes the journey only once in its life, which has long puzzled scientists. How does an insect navigate hundreds of kilometres on a route it has never flown before?
Navigating by the Milky Way
Last year, researchers answered part of that question. By placing a tether around captive moths and projecting stars onto a wall, they showed that bogongs use the Milky Way to steer. The finding made bogong moths the first invertebrates — a broad group of animals that includes spiders, snails and worms — known to use celestial navigation for such long trips.
The moths matter well beyond their own species. They are thought to help plants spread pollen, and they serve as a key food source for the mountain pygmy possum, a critically endangered cave-dwelling marsupial. "They are very, very important to Australian ecosystems," Drinkwater said.
They can also make their presence felt in unexpected places. At the 2000 Olympic Games in Sydney, swarms drawn toward the blazing stadium floodlights caused havoc. Forecasters warned that heavy rain was about to drench the closing ceremony — only to realise the radar had picked up a cloud of bogongs.
A fragile recovery
Researchers are still working to understand what drove the bounce-back, but they believe a spate of wetter weather has helped. And the recovery may prove fragile. With a severe El Niño forecast to send temperatures soaring over the coming summer, scientists fear the rebound could be short-lived.
"It's great they're back, and we're really excited they're back," Drinkwater said. "But we're still worried about them."
via Phys.org Biology (Source)
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