Why swarms of moths are invading Sydney homes right now

Sydney residents have been finding moths in their homes, cars and offices in unusually large numbers this week, sparking confusion over where the sudden swarm has come from. According to gardening expert Rob Palmer, the answer lies hundreds of kilometres inland, in an annual migration that has simply taken a wrong turn.

The insects are Bogong moths, which hatch on the western plains and tablelands beyond the Great Dividing Range. Every year, as temperatures climb, they fly south in huge numbers toward the alpine caves of the Snowy Mountains, where they cluster on rock walls to wait out the warmer months in a kind of hibernation before returning north to breed and die.

Palmer said this year's arrivals in Sydney appear to be young moths making the journey for the first time, and a westerly wind gust has pushed part of the migrating swarm off its usual path toward the mountains. Once disoriented, the moths are drawn toward the glow of a big city instead of the dark alpine caves they are meant to reach.

"They've just been blown off course, they've seen the lights of Sydney, and they're in," Palmer said, adding that the moths are essentially passing through rather than settling in for good. Once conditions change, they will continue on toward the mountains to complete their migration.

The species drew attention a few years ago when drought and poor conditions in its breeding grounds caused numbers to crash, leading to it being listed as endangered. Palmer said that history makes the current mass sighting even more notable, since a healthy migration in these numbers suggests the population has recovered strongly since then.

Beyond their novelty, the moths play a serious ecological role. They are a key food source for the mountain pygmy possum, one of Australia's few hibernating marsupials, which relies on the annual arrival of Bogong moths in the high country to build up fat reserves. When moth numbers dropped during the drought years, possum populations struggled as a result.

For anyone dealing with moths indoors, Palmer's advice is simple: turn off the lights inside and switch on an exterior light, such as a porch or driveway light, to draw them back outside. He noted the moths can still be surprisingly hard to shift once they're inside a dark room, repeatedly bumping into curtains and walls before finding their way out.

Importantly, Palmer said there is no cause for concern about property damage. Bogong moths do not feed on clothing, timber or stored food inside homes, and while their sudden appearance in large numbers can unsettle people who dislike insects, they are considered harmless. The swarm is expected to move through the city and on toward the mountains within a matter of days.