Rats across Britain are evolving a resistance to poison that makes them
almost impossible to kill, scientists have warned.

By Matthew Moore
Last Updated: 4:32PM BST 15 May 2009

Rat: New 'super rats' evolve a resistance to poison

There are now thought to be around 80 million rats in Britain Photo: GETTY

Genetic mutations have produced a new breed of "super rat" with DNA that
protects the vermin from standard toxins, according to Professor Robert
Smith at the University of Huddersfield.

Ratcatchers in Berkshire and Hampshire were the first to report that
their poisons were no longer effective, which experts put down to
increased immunity among the pests.

But as the poison-resistant rats continue to spread, tests have revealed
that they boast an entirely new strand of DNA that wards off attacks
from pesticides.

Swindon in Wiltshire is the latest town to suffer an infestation, with
exterminators reporting a 500 per cent increase in the rodents. Many are
turning to traps, air rifles and even dogs in an effort to keep the
populations under control.

Prof Smith of the university's applied sciences department warned that
"super rats" may be thriving in communities across Britain. The
Government no longer provides funding to track resistance, meaning the
scale of the problem is unclear.

"Natural selection means that when you have a rat population in your
town, poison will kill the ones that aren't resistant, the ones that
survive may have the gene, they then have babies who can receive the
gene themselves," he said.

"There are mutations and changes in their DNA that alter the ability of
rats to deal with these poisons. It appears to be moving west and has
now been located in Swindon and Bristol. It is a warning of things to come."

There are now thought to be around 80 million rats in Britain, a rise of
more than 200 per cent since 2007.

The National Pest Technician Association has said that the scrapping of
weekly bin collections in many councils has contributed to the
explosion, with householders now keeping their rubbish bags outside for
longer.