Rising Rodenticide Resistance in UK: CRRU Calls for Action


The Campaign for Responsible Rodenticide Use (CRRU) UK has reported a concerning rise in the prevalence of anticoagulant rodenticide resistance among rats and house mice. Genetic resistance has been identified in roughly 78% of rats and 95% of house mice, with a small number exhibiting ‘hybrid resistance’ from multiple resistance genes. The spread of both single-gene and hybrid resistances is geographically increasing. The most recent annual study detected a new four-component ‘spretus’ resistance strain in Hertfordshire house mice, thought to originate from interbreeding with Spain’s Iberian mouse species, Mus spretus. London has emerged as a significant hotspot for such resistance.

Between 2020 and 2022, the prevalence of a severe resistance gene, Y139C, has expanded to 30 new sites in England, infiltrating areas previously free from resistance. As a result, England now hosts few rodent populations that remain entirely susceptible to anticoagulants, creating public health risks and accelerating the spread of resistance. To combat this, the CRRU recommends that stakeholders closely monitor local resistance status and follow their five-point action plan. If resistance is detected, adherence to the Rodenticide Resistance Action Group’s guidelines is strongly advised. RRAG is also expected to soon provide updated advice on controlling rodents exhibiting hybrid resistance.