The world is seeing a rapid rise in the occurrence of resistant rats and mice, which some people have coined “super” rodents.  In the UK we have 9 known resistance mutations in rats and 2 in house mice. Using an ineffective anticoagulant product could result in poor control when used against a resistant population AND risks selecting for and spreading the most highly resistant rodents!

What are resistant rodents?

Resistance is the ability to withstand the effects of normally applied concentrations of a chemical. This means that resistant animals can survive doses of an anticoagulant that would normally kill susceptible animals. Resistant rodents have a mutation in their genetic code, a change from one sequence of bases to another, which prevents some anticoagulants from having any effect.

RRAC’s Mapping Tool

To avoid using the wrong anticoagulant rodenticide you first need to know where resistance has been found. Pest control operators are using the RRAC mapping tool to find resistance mutations in their area and to get guidance on which rodenticides will be most effective. Below are images taken from the RRAC website of resistance in Norway rats and house mice in the UK.

 Norway rat resistance













House mouse resistance














How can you help prevent the spread of resistance?

Before you use any anticoagulant rodenticides please visit the RRAC website for the latest updates on where resistance has been found.




Due to financial difficulties created by covid-19, the University of Reading has made the difficult decision to close the Vertebrate Pests Unit. Unfortunately this means that we are no longer able to offer resistance testing at the University or continue our part in the rodenticide resistance testing project.
As this announcement also means that myself and Montse will be leaving the University, we both want to thank you for your enthusiasm and participation in the project. Without your help we would not have been able to collect so many tail samples and fill in so many of the gaps on the maps. We truly appreciate the hard work of everyone involved.
The Campaign for Responsible Rodenticide Use (CRRU) and the Rodenticide Resistance Action Committee (RRAC), who have been funding our research, are in the process of finding alternative laboratories to continue this important work. So if you have tail samples stored in the freezer please listen out for future announcements by these two groups. It is essential that the mapping of resistance mutations continues for both the effective management of rodents and for the environment as a whole.
All of our results will be uploaded onto the RRAC online resistance maps https://guide.rrac.info/resistance-maps.html so please remember to visit their website for the latest resistance updates.
Thank you again for your support.
From the whole team at the Vertebrate Pests Unit.