Rodents in a Trap

I have finally taken one of the rodents – which I caught with a trap, rather than poison – placed it carefully in a plastic bag to avoid contamination, and compared it to a picture in a book – it is, in fact, a vole. It now makes perfect sense that the poison does not work on them.

Thank you, erthwsdm, for providing me with that helpful bit of information. However, I am still at a loss as to how to alleviate the problem.