Billions of Moths Light Up Weather Radar Across Australia

Weather radars across eastern New South Wales have been detecting "rainfall" every evening for weeks, but there's not a cloud in the sky. Scientists believe they're actually seeing billions of bogong moths migrating south to the Australian Alps, and they couldn't be more excited about the discovery.

The moths are flying to mountain caves where they spend their summer, traveling in such massive numbers that meteorology equipment mistakes them for widespread light rain. The Bureau of Meteorology confirmed their radars aren't broken but are instead picking up one of nature's most spectacular journeys.

"It's brilliant," says Associate Professor Kate Umbers from Western Sydney University, a leading moth researcher. The radar signals could help scientists reconstruct bogong moth populations and movements going back to World War II, filling critical gaps in knowledge about these mysterious insects.

Bogong moths faced a catastrophic population crash in 2017, and efforts to list them as federally endangered were rejected in 2025 because scientists lacked enough monitoring data. The current swarms suggest their numbers are bouncing back, but researchers still know surprisingly little about where the moths come from or where they go.

Umbers and her team tagged 14,000 moths earlier this year at Mount Kosciuszko, hoping to track their movements across Australia. Every single tagged moth went missing, highlighting just how elusive these insects are despite traveling in billion-strong swarms.

The moths shelter in alpine caves during summer, with up to 17,000 roosting within a single square meter. These caves are vulnerable to warming from climate change, which led to the moths being listed as endangered on the international IUCN red list based on habitat threats rather than population counts.

Weather radar works by sending out radio waves that bounce off water particles and return to the antenna. The same waves can reflect off smoke, ash, birds, and apparently moths when they fly in large enough numbers.

The Bright Side

This accidental discovery opens up an entirely new way to study and protect bogong moths. Scientists can now analyze historical radar data stretching back decades to understand population trends and identify patterns in the moths' mysterious migration. They might even discover previously unknown roosting sites hidden in remote alpine areas.

In a creative new tracking effort, Umbers' team recently caught 500 bogongs in the Blue Mountains and painted their wings blue. Anyone who spots a blue-marked moth and reports it to bogong.org will provide valuable information about these epic travelers.

The last time moths famously appeared on radar was during the 2000 Sydney Olympics, when organizers panicked about rain clouds approaching the closing ceremony. The "clouds" turned out to be swarms of bogongs attracted to the stadium lights, creating an unexpected moment of natural wonder at a global event.

This year's radar phenomenon shows that nature still has the power to surprise us with its scale and beauty, even as it hands scientists the tools they need to ensure bogong moths continue their ancient journey for generations to come.