Dr Helena Vance, Science & Climate Correspondent: Australia is enduring one of its worst mouse plagues in living memory. From the grain belt of New South Wales to the fields of Queensland, farmers are reporting losses of entire harvests, while rural communities face a biblical influx of rodents. The question on everyone’s lips: why now? The answer, as ever, lies in a combination of climate, ecology, and human land management.
Mice plagues are not new to Australia. In fact, they follow a pattern that is well understood by ecologists. House mice (Mus musculus) are opportunistic breeders. Under optimal conditions, a single female can produce up to 10 litters per year, each with 6-8 pups. That is exponential growth. But ‘optimal conditions’ require ample food and shelter. In the Australian grain belt, that means abundant grain harvests and mild, moist conditions that allow for extended breeding seasons.
Enter climate change. The 2020-2021 period saw a remarkable shift from drought to deluge. La Niña events brought heavy rains across eastern Australia, ending a long dry spell. The rain revitalised crops and pastures, but also created a perfect habitat for mice. With plenty of food (spilled grain) and cover (thick stubble), the mouse population exploded. The key metric is the ‘mouse index’, which measures the percentage of traps containing rodents. In early 2021, that index exceeded 70% in some regions, a level not seen since the early 1990s.
But this is not just a natural cycle. Human modifications of the landscape have amplified the problem. Intensive grain farming, with vast monocultures of wheat, canola, and barley, provides a continuous food supply for mice. Moreover, the shift towards minimum tillage agriculture leaves more crop residue on the soil surface, offering shelter. In effect, we have created a massive, year-round pantry and hotel for mice.
The consequences are devastating. Mice consume and contaminate grain stores. They gnaw through wiring in combines and silos, causing fires and machinery failures. They spread diseases like leptospirosis and salmonella, threatening human and livestock health. And they wreak psychological havoc on farming families, who live with the constant sound of scurrying and the smell of dead rodents.
Control methods are limited. Poisons are used, but mice can develop resistance. Zinc phosphide, a common rodenticide, is effective but can kill non-target species such as raptors and dogs. There is talk of biological controls, like introducing a virus that specifically targets mice, but the precedent for such interventions is fraught with ecological complexity. In the meantime, farmers resort to breeding flocks of feral cats and setting up electric fences, but these are stop-gaps.
The bigger picture is sobering. As the climate warms, the frequency of extreme weather events, including the ‘boom-bust’ cycles that fuel plagues, is expected to increase. For Australia, a nation already battered by fires, floods, and heatwaves, the mouse plague is yet another symptom of a biosphere under stress. It reminds us that ecological systems do not respect our boundaries. They respond to physical realities: heat, water, and food.
What is to be done? In the short term, farmers are calling for greater research into integrated pest management, including the development of smarter poisons that target mice without harming the ecosystem. In the longer term, the conversation must turn to how we manage agricultural landscapes. Diversifying crops, restoring natural predators, and building resilience into farming systems are not soft options; they are hard necessities.
For now, the mice are winning. But their victory is not inevitable. It is a call to action for a scientific and policy response that matches the scale of the crisis. As I sit in my study, thousands of miles away, I can still feel a sense of calm urgency. The data are clear. The physics and biology are unambiguous. We ignore them at our peril.
