Naked and afraid: The extraordinary reason moths are haunting your shower

They come for us at night when our guard is down. Moths are bearing down on the suburbs, haloing streetlamps, invading bedrooms and, according to many reports across Sydney, launching fuzzy and frightening ambushes on people in the shower.

Many of these stubborn house guests are of a species undertaking one of the greatest migrations on Earth which recent research has revealed as all the more astonishing by identifying the insects’ exceptional navigation system.

Billions of bogong moths fly up to 1000 kilometres from their winter breeding grounds, such as the plains of central Queensland, to shelter from summer heat in the cold mountain caves of the Australian Alps.

“They don’t always come through Sydney,” Associate Professor Kate Umbers, a bogong researcher from Western Sydney University, said. “Some years we get a bazillion of them, and other times we get an inconspicuous number. It’s based on wind.”

We already knew the moths, like many other animals, use Earth’s magnetic field to navigate. But Professor Eric Warrant, an Australian biologist attached to Sweden’s Lund University and a collaborator of Umbers’, suspected something else was at play: starlight.

Warrant built a flight arena from black felt in a field lab in the Snowy Mountains to test the moths’ navigational prowess, in an experiment reported in Nature in June.

The arena was free from magnetic metals – think Magneto’s plastic prison in X-Men 2 – and housed within electromagnetic coils designed to negate Earth’s magnetic field, so researchers could isolate and test the moths’ ability to navigate solely using the stars.

The researchers tethered moths to a fine stalk and projected the night sky onto the roof of the arena.

What happened next, Warrant recalled, astounded them. The moths flew in the right direction of their migratory route, even when severed from Earth’s magnetic field. When Warrant flipped the projected stars 180 degrees, the moths flew the opposite way. Finally, when the stars were scrambled, the moths seemed lost and fluttered in every direction.

Warrant had proved bogongs use the stars as a compass to fly in a specific direction – an ability, to the researchers’ knowledge, shared only by humans and some night-flying songbirds. This extraordinary power gives the moths two methods of finding their way. If it’s cloudy, they use the magnetic field. And if a geomagnetic storm disrupts that field, they can follow the stars.

That means those little brown bodies find their way to our porches and bathrooms by following a map made from the invisible force field thrust from the electromagnetic core of Earth’s molten belly and the light of the galaxy. That’s pretty startling for an insect fuelled by minuscule sips of eucalyptus nectar with a brain one-tenth the size of a rice grain.

If the monarch butterfly is the “king of insect migration” for its multi-generational journey from Canada to Mexico, Warrant writes in Current Biology, then the bogong moth is its dark lord.

For millennia, the bogongs have served as a deliciously nutty food source for Aboriginal peoples who gathered the insects from their alpine caves and roasted them for summer feasts.

The migration also delivers a life-giving smorgasbord of winged fat and protein to alpine creatures, including the mountain pygmy possum, whose populations have crashed in tandem with that of the moths.

The moths are clawing their way back from near oblivion after drought – in concert with a raft of other threats, including irrigation, land-clearing and insecticides – devastated their numbers in 2017.

Go back another decade to 2007 and you might remember clouds of moths swarming Parliament House and flocking in clouds so thick they were mistaken for thunderstorms.

“Last year we were at roughly 50 per cent of the pre-2017 crash numbers,” Umbers said. It’s too early to know if this year is a strong one for the moths, at least relative to their much-depleted populations of recent years, but the first bogongs have started to arrive at the foothills of the Alps in good numbers.

More information on the moths’ movements and how they use their alpine “aestivation”, or dormancy, sites over summer is desperately needed.

Their cold mountain caves are quickly growing too hot under climate change to provide the cool shelter the moths need. Umbers is working to figure out if they’ve started to abandon some of the fastest-warming sites near Canberra.

The moths are listed as endangered on an international level under the IUCN Red List but not under Australia’s EPBC Act threatened species list due to a lack of data.

To help rectify that, scientists have asked moth spotters to snap photos of bogongs they find outside or in their homes and upload them to Zoos Victoria’s Moth Tracker website, or iNaturalist.

Bogongs are mottled brown, about 2.5 to 3.5 centimetres long, and sport a dark stripe on each wing, studded with two spots.

“If people aren’t sure if they’ve got a bogong or not, it doesn’t matter. Just upload it,” Umbers said. “It’ll be really, really valuable information.”

Umbers is also preparing to tag 10,000 moths in late summer with tiny stickers to help track where, exactly, they fly after their slumber in the caves. The public will be asked to keep a lookout for the tagged moths once the new program, Bogong Watch, gets under way.

A similar project in the US has tracked migrating monarch butterflies since 1992.

“It’s a mad-slash-genius-slash-insane scientist idea,” Umbers said of the plan to tag thousands of moths for the pilot study. “History will decide if it works.”

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