Australian farmers are battling another potential mouse plague – what is causing it?

Got a mouse in your house? That thought alone may terrify you.

Now imagine if mice were scampering through your house, rummaging in your pantry or even running across your face at night.

That sounds like the stuff of nightmares, but it’s what many Australians have experienced when living through a mouse plague.

Mouse plagues can be economically and psychologically devastating, particularly for rural communities. This is because mice destroy crops, spread disease and damage the natural environment.

Currently, farmers across two Australian states are battling a potential mouse plague. And it’s an unsettling reminder of the mouse plagues of 2020 and 2021 that ravaged farms and rural communities across Australia’s east coast.

So what’s causing this latest plague? And how are farmers coping?

When mice take over

Mice have been a part of the Australian environment ever since they arrived with the First Fleet in 1788. Since then, they’ve rapidly bred and spread all around the country.

In some areas, mice populations can reach plague proportions. This means there are at least 800 mice per hectare of land. The first documented mouse plague happened in 1872 in the South Australian town of Saddleworth.

Mouse plagues often occur as a result of cyclones, floods or other weather events that increase rainfall and soil moisture. Good rains help native plants grow, but they also fuel bumper harvests in key grain-growing regions. These are perfect places for mice to breed because they have warmer climates and plentiful food sources, such as grain. In such conditions, mice can prolong their breeding season by several months and even produce several litters each season.

Yet another plague

Just this week, farmers in Western Australia and South Australia have been inundated with mice. In parts of WA, some farmers have found 3,000-4,000 burrows in just one hectare of land. And SA mouse numbers are at their highest levels in at least four years.

Unfortunately, the timing could not be worse. That’s because many farmers are about to start seeding – the process of putting seeds into the soil to grow crops – after recent rains. These farmers are now at risk of losing their crops before they even have the chance to germinate.

This all suggests this latest mouse plague could be as bad as the plagues of 2020 and 2021 that affected communities across SA, western Victoria, New South Wales and southern Queensland. Over an 11-month period, millions of mice devoured spring crops and destroyed farm machinery.

This series of plagues cost the agricultural sector an estimated A$1 billion, with many farmers and local businesses struggling to make ends meet. And this economic uncertainty took an immense psychological toll. This plague event also exposed rural communities to rodent-related disease, leaving some residents highly anxious or fearful.

What can farmers do?

Farmers in WA and SA are turning to mouse control methods as a way to curb mice numbers. The main method is laying mouse bait which, when ingested in the right dosage, is fatal for mice.

Zinc phosphide is widely used by farmers with large cropping operations. Recent studies suggest using higher doses of zinc phosphide – which currently requires farmers to get a special permit – can reduce mouse numbers by up to 90%. However, Australia’s pesticide regulator has disputed this research and has refused to make more concentrated baits available. One reason is these baits, if used incorrectly, may cause harm to non-target species especially seed-eating birds such as Crested pigeons, galahs and Corellas.

Some mouse baits pose a direct risk to native wildlife. Our research team has studied the impacts of a type of toxic bait, known as second-generation anticoagulant rodenticides. The most widely-used are brodifacoum and bromadiolone. Scientists have found lethally high levels of both rodenticides in populations of native owls, reptiles and even threatened quolls.

However, the federal pesticides regulator recently banned the sale of these products to retail consumers. As a result, many people will be understandably looking for alternatives and should consider using first generation or alternative baits and other approaches.

Farmers are also exploring other mouse control strategies. Experts recommend investing in mouse-proof grain storage and plugging gaps at home. One farmer has even developed a home-made mouse-proof fence that has helped manage mouse numbers. Unfortunately other methods such as snap traps – devices designed to capture and kill mice – are unlikely to significantly curb mouse numbers during a plague event.

Anyone who’s lived through a mouse plague knows how destructive, both economically and emotionally, they can be. So let’s hope this latest plague event comes to a swift end. That way rural communities across WA and SA can get back on their feet.