Mutant rats are appearing across the West to become resistant to common poisons, university scientists have warned.
An 18-month project to DNA test the rat populations in Bath, Wiltshire, Gloucestershire, Somerset and Bristol has discovered three-quarters of the vermin have mutated to be resistant to the commonly sold poisons like Bromadiolone and Difenacoum.
Dr Dougie Clarke, the head of biological sciences at Huddersfield University, tested rats across the country and discovered that in the West of England, more mutant rats have evolved than anywhere else.
He warned that within ten years, as the genetically mutated rats breed with each other, the entire population could be resistant to poisons.
He blamed pest controllers for not putting down strong enough doses of the poison – in effect the rats are fattened up by the bait and grow immune to the weak poisons, treating them like a vaccine.
“Some pest control companies are still using the same rodenticides – Bromadiolone and Difenacoum – in areas where there are resistant rats and things need to change,” he said.
“We’re wiping out the normal susceptible rats and we’re going to be left with resistant rats only in this area so alternatives have to be found so we’re not using these poisons,” he added.
Now there are fears that the poisons that are building up in rats bodies but not killing them could be passed up the food chain if the rats are eaten by cats or birds of prey.
“If you’re putting poison down and it’s one of the mutant strain, if it takes a belly full of rodenticide you may as well be giving it Sugar Puffs,” said Andy Bellows, a ratcatcher from Gloucester.
Dr Clarke hopes that now the current project is completed, a larger, nationwide strategy will follow.
The term “super rat” is quite appropriate, says Dr Clarke. The creatures that are unaffected by routine poisons have not become resistant because of the evolutionary process. The timescale is too short for that. Instead they have a genetic mutation, he said.
“They are no bigger than ordinary rats, but you could call them ‘super rats’ because you cannot poison them with a normal rodenticide. It is in the genes and is not some sort of physiological adaptation.”
It is not thought that any super rats are resistant to the more powerful poisons.
“In one area every single rat we analysed was resistant and infestation was so bad that the regional council applied to the Health and Safety Executive for emergency use of the stronger rodenticides and they were eliminated within two weeks,” he added.