The moths are back, and New South Wales has noticed

For once, a swarm in New South Wales has not prompted panic, only a fair amount of astonishment. Over the past few days, residents have reported clouds of bogong moths across coastal areas, and scientists say the surge is cause for encouragement rather than alarm.

Hundreds of sightings were posted over the weekend to the Bogong Watch page on iNaturalist, part of a citizen science project run by Invertebrates Australia. Spring is the moth’s migration season, when vast numbers travel up to 1,000 kilometres to a handful of cool caves in the Australian Alps, where they spend the summer avoiding the heat. This year, the movement appears to be especially strong.

Linnea Emneby, who manages Bogong Watch, said the project’s volunteer “sentinels” around Mount Kosciuszko were reporting unusually high numbers. Three households in New South Wales each recorded dozens of moths on Monday, while one sentinel counted more than 200 on Sunday night. The insects are small, about the size of a 50-cent piece and weighing roughly a third of a gram, but they matter far more than their weight suggests.

They are important culturally and ecologically, Emneby said, because they pollinate plants and also feed the critically endangered mountain pygmy possum. That alone would make their return noteworthy. The fact that they are appearing in such numbers after years of decline makes the story more striking still.

Dr Marissa Parrott, a reproductive biologist at Zoos Victoria, which runs the separate Moth Tracker program, said the reports had been coming in steadily and that the scale this year had surpassed expectations. Sightings have risen over the past two years, but September alone has already produced more reports than all of last year. Most of the larger numbers are coming from New South Wales and the ACT, while Victoria remains behind.

Parrott said wetter, cooler weather may have helped create better conditions for the moths. She also noted that their migration does not arrive in a neat procession; it comes in waves, sometimes taking days or weeks to complete. In a more ordinary year, these swarms would be visible across Canberra, Sydney, Newcastle and Melbourne, the southeastern corridor where the species has long moved.

That ordinary picture has been badly disrupted. An estimated 4 billion moths once reached the Alps each year, before the population collapsed by as much as 99.5% between 2017 and 2019. The species has been listed as endangered by the International Union for Conservation of Nature since 2021, though it is still not listed as threatened under federal conservation laws. Bureaucracy, as ever, is slower than reality.

There is still reason for caution. Parrott pointed to the strongest El Niño on record and the drier, hotter conditions it can bring, warning that the next couple of years could prove difficult even if current numbers look promising. The moths generally migrate inland, though weather and wind can push them elsewhere; last year’s Moth Tracker sightings even showed some reaching New Zealand.

For now, the advice is simple enough. Turn off unnecessary outdoor lights, avoid insecticide use, and report sightings to Moth Tracker or Bogong Watch. If one ends up indoors, place it gently back outside. Females can lay up to 2,000 eggs, and the moths do no damage, do not eat clothes and quietly help gardens along the way. It is not often that a mass arrival of insects leaves people relieved. This time, it should.

Written by Martina Kirchner martina.kirchner@alpineweekly.com