"Super-rats" could be in Bristol and Swindon
Fears are being raised that new "super-rats", resistant to normal poisoning techniques, may have arrived in the West Country.
DNA tests on rats' tails collected in Bristol and Swindon confirm the presence of a mutant gene which helps rodents develop the resistance.
A survey of councils in the West showed three quarters had seen a recent rise in the number of rat-related call outs.
Scientists at the University of Huddersfield are studying super-rats.
Professor Robert Smith, from the university, said: "It's the first time we've found this mutation that far west.
"In both Swindon and Bristol there are resistance genes which are likely to build up under selection with use of poisons and there may be a problem that's building up for the future."
As well as the idea of "super-rats," revamped rubbish collections, milder winters, more food in compost heaps and the increased use of bird feeders are all possible reasons why there are more rats than ever in the region.
The story features on Inside Out West on BBC One in the West region at 1930 BST.
Viewers outside the West can see it on Sky digital satellite channel 986 and on the BBC iPlayer.