If you have checked the rain radar recently and wondered why the garden remains dry, the explanation could have wings.
Swarms of migrating Bogong moths are believed to be producing echoes resembling light rainfall on Bureau of Meteorology radar across parts of eastern NSW, including the Sydney region.
The Bureau has acknowledged that large numbers of the insects could be contributing to apparent rain on radar images, particularly around sunrise and sunset. Modern radar can distinguish between different types of objects, but biological activity can still create conspicuous echoes.
Weather radar works by sending out pulses of microwave energy and measuring the signals reflected back. Rain, hail and snow produce echoes, but so can insects, birds, buildings and terrain.
When enough insects are airborne together, their combined reflections can create a pattern that viewers might interpret as rain. The Bureau’s explanation of radar technology makes clear that a coloured patch on the screen does not always mean precipitation is reaching the ground.
There is an important distinction for Hawkesbury residents planning outdoor work or watching for rain: these reports concern radar imagery. They do not establish that moths are making the Bureau’s weather forecasts unreliable.
Nor should every unexpected radar patch be blamed on Bogongs. The Bureau has cautioned that other atmospheric conditions, including temperature inversions, can produce similar effects, making it difficult to attribute individual echoes entirely to moths.
The insects are undertaking their annual spring migration towards cool caves and rocky shelters in the Australian Alps, where they spend the summer.
Strong winds can push migrating moths towards coastal communities. Artificial lights can then attract them into towns and homes, drawing them away from their route. Researchers say these factors help explain the substantial gatherings reported across NSW this spring.
Despite their conspicuous presence, Bogong moths remain a conservation concern. The species was added to the International Union for Conservation of Nature’s endangered list in 2021 following a severe population collapse.
Residents can help by switching off unnecessary outdoor lighting during migration and submitting photographs to Zoos Victoria’s Moth Tracker. Records help researchers understand where the insects are travelling and when they arrive. Experts can also verify whether a photographed moth is a Bogong.
For now, a dry evening beneath a colourful radar display may offer a glimpse of a remarkable wildlife journey.
