Bogong Moths Invade Sydney and Coastal NSW: What's Behind the Surge?

Sydney, Canberra, and coastal NSW are currently experiencing an unusual influx of bogong moths, with millions of the insects migrating to cool mountain caves for a summer hibernation. The surge in moth numbers has been noticeable in urban areas, with swarms appearing in any crevice they can find and staying far longer than usual.

Why are there so many moths?

Caitlyn Forster, a lecturer in entomology at the University of Sydney, attributes the large number of moths to several factors. "Bogongs actually use the stars to navigate, which means they are impacted by lights, and particularly in urban areas where we've got a lot of lights on our streets and houses," Dr Forster said. She also noted that strong winds could play a role in causing large moth numbers to appear, particularly if they get blown off their migration course.

Dr Forster also highlighted the generational gap in insect knowledge, noting that the number of bogong moths for this time of year was normal, "we just haven't seen it for quite a while". "There has been a drop in their populations that was really noted around 2017 and 2019," she said. "[But] something that's really interesting is the idea of a shifting baseline centre. A lot of younger people don't actually know a point where there were lots of insects around because there's not been a lot of insects around for quite a long time."

Conservation efforts

Marissa Parrott, a senior conservation biologist at Zoos Victoria, said that 99.5 per cent of the bogong moth population had been decimated, making them almost "undetectable" in recent years. However, she noted that it is "brilliant to see the bogong moth population bounce back". "We are so excited to see the numbers of bogong moths right now, it's the best year in nearly a decade for them," she said. "It's a really great start of a recovery … and we do hope it continues."

Researchers are working to understand the moths' distribution and flyways by marking them with blue paint dots and monitoring their movements. Citizen scientists are being urged to report sightings of the marked moths as part of conservation efforts.

When will they leave?

Dr Forster said it could be days or weeks before the moths disappear from urban areas. "It's an interesting question because it could be pretty soon … but we're sort of just waiting out to see how long they'll hang around," she said. She encouraged people to take the opportunity to appreciate the moths and get out in nature, particularly with children.

How can I help their journey?

To help the moths, people are advised to turn off unnecessary lights, which may lure them away from their path. The public is also encouraged to take a photo of any moths they see and upload it to the moth tracker website, Bogong Watch.

Some people have been removing moths using a funnel and a jar, while others have been sharing ideas online for helping the moths on their migration.