Vast swarms of bogong moths are suspected of fooling weather radars across eastern New South Wales, with the insects showing up as light rainfall on clear, dry evenings. The Bureau of Meteorology says its radars are not malfunctioning, and researchers hope the phenomenon could yield vital data on one of Australia's most under-threat insects.
Bogong moths are flying south to shelter in the cool caves of the Australian Alps over summer, in numbers large enough that conservationists are celebrating a slow recovery from a catastrophic population crash in 2017. The Bureau of Meteorology said in a statement: 'It is possible that radars across eastern New South Wales are detecting bogong moths.' The bureau said its radars were not malfunctioning, and that 'large numbers of insects can look like very light widespread rain, particularly near sunrise and sunset.'
ABC meteorologist Tom Saunders reported widespread rain lighting up the radar like clockwork each evening for the past few weeks, despite clear skies and no rain.
Radar works by bouncing radio waves off water particles to detect precipitation, but the waves can also reflect off smoke, ash, birds and insects. The bureau confirmed increased echoes on NSW radars that were not precipitation, though it cautioned that other atmospheric factors could be involved.
If moths are the cause, the radar signatures could be a research goldmine. 'It's brilliant: it provides us with an example of what the moths look like on satellite radars,' said Associate Professor Kate Umbers, a moth researcher at Western Sydney University. 'Now we can go back through the records as long ago as World War II to look for signatures of big clouds of moths.'
Federal efforts to list the bogong moth as endangered were rejected in 2025 by then environment minister Tanya Plibersek because of gaps in monitoring and population data. The species is listed as endangered on the IUCN red list, but that status reflects the vulnerability of its alpine cave habitat to climate change rather than its unknown population size.
Umbers and her team tagged 14,000 moths at Mount Kosciuszko earlier this year, none of which have been relocated. In a renewed effort, they have painted blue marks on 500 moths in the Blue Mountains, asking the public to photograph and report any sightings to bogong.org. The last well-publicised case of moths on radar was during the 2000 Sydney Olympics closing ceremony, when apparent rain clouds turned out to be bogongs drawn to stadium lights.
Analysis
Why This Matters
- The bogong moth population crashed in 2017 and is only now showing signs of recovery; radar data could give scientists a way to measure that recovery.
- Federal endangered listing was rejected in 2025 over missing population data, and radar signatures could help fill those gaps.
- Knowing where the moths go matters because their alpine cave habitat is vulnerable to climate change.
Background
Bogong moths are known for their annual migration to the cool caves of the Australian Alps, where up to 17,000 can roost within a single square metre. The species suffered a catastrophic population crash in 2017, and conservationists have been watching for signs of recovery. Because the moths' exact migration routes are unknown, researchers have struggled to build the data needed for federal threatened species protection. The moths are listed as endangered on the IUCN red list, but that listing is based on the vulnerability of their alpine caves to a warming climate, not on population numbers.
Key Perspectives
Scientists and conservationists: Radar echoes offer a new, historically deep source of data. As Kate Umbers put it, researchers can go back through records dating to World War II to look for signatures of big moth clouds, potentially reconstructing decades of movement and discovering unknown roosts.
The Bureau of Meteorology: The bureau stresses that its radars are working correctly and that insects can legitimately appear as light rain on its displays. It also cautions that other atmospheric factors may be contributing to the echoes, so the moth explanation is not yet confirmed.
Government decision-makers: The federal endangered listing was rejected in 2025 by then environment minister Tanya Plibersek because of gaps in monitoring and population data. Until those gaps are closed, the moths will not gain federal protection despite their international red list status.
What to Watch
- Whether anyone spots and reports a blue-painted bogong moth, which would give researchers their first confirmed tracking point.
- Whether analysis of historical radar records can produce a reliable signature for moth swarms and help reconstruct past population sizes.
- Any renewed attempt to list the bogong moth as endangered federally once the data gaps are addressed.