Bogong Moths in Sydney: Why This Spring's Visitors Are a Good Sign

Why Sydney's Bogong Moths Are Back on Our Radar

If a big brown moth has just bumped into your hotel or Airbnb window in Sydney, put the shoe down. There's a fair chance it's a Bogong moth, one of the great long-distance travellers of the Australian bush. It's also endangered.

Maisy filmed the ones in the video above feeding on the Pride of Madeira flowers in our Sydney garden this spring. We watched them for longer than we'd like to admit. Hit play first, it's three minutes, then come back here for the bits that didn't fit: how to tell a Bogong from any old moth, what to do if one ends up in your room, and how a photo on your phone can help the scientists working out whether this species is on the mend.

Why Bogong moths in Sydney are a big deal this spring

If you live in Sydney, this isn't normal. It used to be. Plenty of locals who grew up here in the 80s remember spring nights when Bogongs crowded every porch light. Then, from 2017, they all but disappeared. Severe drought in their breeding grounds is the leading suspect, and estimates of the crash run from 98 to 99.5 per cent depending on who you ask. In 2021 the IUCN listed the Bogong moth as Endangered.

So when sightings started stacking up this September, scientists sat up. Reports have come in from Gunnedah to Balmain, from Kurrajong Heights in the Blue Mountains, and down the coast to the Illawarra. One listener told ABC Radio Sydney the boot of their car in Penrith was lined with them. It's too early to call it a recovery. One good spring doesn't undo a decade. But it's the most hopeful sign in years, and it's happening right on our doorstep.

A 1,000 km trip, navigated by the stars

Every spring a new generation of Bogongs leaves breeding grounds across southern Queensland, inland NSW and western Victoria, and heads for cool caves and rock crevices in the Australian Alps, up to 1,000 km away. They fly at night and steer by the stars, with the Earth's magnetic field as a backup. Research led by Professor Eric Warrant of Lund University found they're the first invertebrate known to use the stars for long-distance navigation. (We have Google Maps and still miss the turn-off.)

Here's the part that gets us. None of these moths has done the trip before. Each generation makes it once, finds caves it has never seen, waits out the summer heat packed shoulder to shoulder on the rock, then flies home in autumn to breed. That summer rest has its own name: aestivation, the warm-weather cousin of hibernation.

For thousands of years, Aboriginal people gathered in the high country when the moths arrived, and the Bogongs were an important food.

Why they end up on Sydney balconies

Sydney isn't on the flight plan. Experts say strong westerly winds this year have pushed more moths than usual towards the coast. One observer watched thousands of them fly in off the ocean at Barrenjoey Point, on Sydney's northern tip, just after sunset on 1 October.

Once they're over the city, two things pull them down: lights and nectar. Bright lights scramble their navigation, and flowering gardens give them fuel for the rest of the journey. Ours chose the Pride of Madeira. Good taste, we thought.

The moth that switched off Parliament House

Sydney is hardly the first city to get a visit. In October 1990, so many Bogongs swarmed Parliament House in Canberra that the acting Speaker ordered the lights off. Office lights, flagpole lights, garden lights, even the street lights on Parliament Drive. Staff have found them in coffee mugs, desk drawers and politicians' hair over the years. These days the building's external lights carry UV filters, which is the most diplomatic solution Parliament House has come up with in a while.

Sydney had its own moment in 2000, when a Bogong swarm turned up on weather radar during the Olympics and was mistaken for a rain cloud.

How to spot a Bogong moth

A Bogong is about 3 cm long and brown, with a distinctive dark stripe running down each wing. That stripe is the giveaway. Look for them from dusk onwards, around flowering plants and outdoor lights, any time from September to December.

They're harmless. They don't bite, sting or eat your clothes. If you're visiting Sydney this spring, take a slow walk through a leafy suburb in the hour after sunset and check the flowering shrubs near streetlights. It's the cheapest wildlife tour in town.

Found one in your room? Here's what to do

Don't squash it. Turn off the indoor lights and leave one outside light on, and most moths will find their own way out. Sydney's Northern Beaches Council recommends exactly this.

If one is stuck, use the glass-and-card trick. Gently pop a glass over the moth, slide a card underneath, carry it outside and let it go in the evening, which is when Bogongs fly. Thirty seconds of your time, and it's back on its way to the Alps. In a hotel, keep the curtains closed after dark if the lights are on. You'll save yourself the 2am visitor.

Your photo can help the scientists

This is where you come in. Researchers still don't know the moths' full flight paths, and sightings from the public are filling the gaps. If you spot one, take a photo and log it with one of these:

• Bogong Watch at bogong.org, run by Invertebrates Australia with Western Sydney University.

• Moth Tracker from Zoos Victoria.

• iNaturalist, the free citizen science app.

Not sure it's a Bogong? Upload it anyway. Bogong Watch says every moth observation is useful, even if yours turns out to be something else.

Two things worth knowing. Researchers have marked 500 moths in the Blue Mountains with a small blue paint dot. If you see one, don't touch it, just photograph it and report it at bogong.org. And the team is trying to work out which plants Bogongs feed on during the migration, so they can advise on Bogong-friendly gardens. If you catch one feeding, note the plant. That's exactly the kind of detail they're after.

The tiny possum waiting at the top

The Bogongs' arrival in the Alps matters to more than the moths. The mountain pygmy-possum, Australia's only hibernating marsupial, wakes up hungry in spring and relies on Bogongs to refuel. When the moths crashed, the possums were in trouble too, and researchers came up with a fix involving something called "bogong bickies". We won't spoil it here. Watch the video if you need further clarification.

Watch the video, then look closer

That's the long version of a short film. The video has Maisy's garden footage, the journey on a map, the Olympic radar story and the possum bickies, all in about three minutes. Watch it at the top of this page, and if you'd like more of Sydney from two people who live here, subscribe to Inspirational Hunter on YouTube.

And if a Bogong lands on your balcony this spring, say hello. It's come a long way.