Domestic cats are lethal hunters, killing at least 275 million other animals a year in Britain, a report showed today.
The apparently cuddly pets prey on a number of declining and endangered species, including water voles and dormice, said the Mammal Society.
The survey, called Look What the Cat Brought in, found that the average household cat caught or killed between 30 and 40 creatures a year.
With an estimated nine million pet cats in this country, the haul amounted to 200 million mammals, 55 million birds and 10 million reptiles and amphibians.
Survey co-ordinator Michael Woods said the effect on species already under threat was a "considerable cause for concern".
The society studied records from 964 cats in about 600 households over a five-month period - during which the pets killed more than 14,000 animals.
It found that mice were the most popular prey, with the sample killing 4,196, against 1,949 voles and 946 shrews.
This meant cats killed more than 80 million mice in Britain.
Cats also hunted down larger mammals, including high numbers of rabbits, weasels, stoats and grey squirrels.
But they were very poor at killing rats, having captured only 162 in the survey - probably because the rodents fight back viciously.
But cats also targeted many bats, which are very slow to reproduce, possibly killing 230,000 a year across the country.
Birds were also heavily preyed on, with a total of 3,383 taken by the cats in the survey.
House sparrows were most popular, followed by blue tits, blackbirds, starlings, thrushes and robins.
Frogs, toads, newts, lizards, grass-snakes and slow-worms were the final, items on the cats' menus.
Two-year-old cats killed the most, the survey showed, although some of the best hunters were grizzled eight and nine-year-olds.
Mammal Society chairman Professor Stephen Harris said cat owners should keep their pets indoors at night to ensure the future of British wildlife.
"This survey has given a clear indication of the threats cats pose to Britain's animal populations," he said.
Mr Woods, who is also the society's vice-chairman, added: "Although it is unlikely that cats alone will cause any species to become endangered in Britain, for those which are already under pressure for other reasons, such as thrushes, harvest mice, grass snakes and slow-worms, cats could tip them over the edge.
"Cats can roam up to 1km (over half a mile) away each night and have a home range of 28 hectares.
"It's particularly bad where you have houses being built on the edge of towns by the countryside, near the habitats of many endangered species."