Millions of bogong moths embarking on their annual nocturnal trek to the Australian Alps have triggered phantom storm alerts on weather radars across New South Wales, mimicking sudden bands of heavy rainfall.
Nocturnal departures light up the screen
As darkness falls across regional New South Wales, evening weather-watchers consulting radar displays could easily mistake the blooming green and amber clusters for an incoming front. Instead, ABC News NSW reported, the sudden bursts of atmospheric activity are vast clouds of migrating insects lifting simultaneously into the night breeze.
The moths, which breed in the fertile pastures of Queensland, western New South Wales, and Victoria, travel hundreds of kilometres south each spring to escape punishing inland summer temperatures. Because meteorological radar systems emit electromagnetic pulses that reflect off small airborne objects, dense swathes of insects—known in meteorology as biological scatter, or bioscatter—frequently return a signature indistinguishable to the untrained eye from light or moderate precipitation.
An alpine lifeline takes flight
For ecologists and conservationists, the radar anomalies represent far more than a technical curiosity; they offer heartening evidence of an ecological recovery. The bogong moth (Agrotis infusa) plays an indispensable role in the fragile ecosystem of the Snowy Mountains. During their summer aestivation within cool, high-altitude granite crevices, the lipid-rich insects provide crucial nourishment for the critically endangered mountain pygmy-possum, alongside native bird and bat populations.
Between 2017 and 2019, severe drought conditions across inland breeding territories decimated the species, reducing populations by an estimated 99.5 per cent and precipitating starvation events among alpine mammals. The catastrophic collapse prompted the International Union for Conservation of Nature to formally list the moth as endangered in 2021. The substantial blips now sweeping across southern radar installations suggest that improved seasonal moisture across western breeding grounds has enabled a welcome demographic rebound.
Navigating towards high country peaks
Travelling under cover of darkness, bogong moths navigate using a combination of the Earth's magnetic field and visual cues such as celestial landmarks. However, their migratory journey is increasingly fraught with modern obstacles. Bright artificial lighting across regional centres and urban sprawls regularly draws the nocturnal travelers off course, trapping thousands in outdoor lights, car parks, and public buildings.
Canberra and southern regional centres frequently witness dense gatherings of disoriented insects clustering in sheltered recesses and stairwells during peak transit weeks. Biologists have reiterated calls for urban residents and commercial building managers within migration corridors to switch off non-essential external lighting, granting the moths safe passage to their high-country destination.
While the migratory influx is expected to cause sporadic radar confusion for meteorologists over the coming weeks, the presence of the insect plumes confirms that one of Australia's most remarkable natural migrations is once again under way.