Rats eat mussels

20/09/2001

Britain faces a massive increase in its rat population - because they've discovered how to eat mussels.

The rodents are diving down to a rich new food supply and coming up trumps.

The phenomena has been discovered for the first time by Cambridge University biologist David Aldridge.

Piles of discarded mussel shells can now be found on the banks of the River Nene near March in Cambridgeshire. They remove the back third of the molluscs to get at the meat inside, which can be up to 10cm long.

'The rat population has already exploded and will continue to explode,' said Dr Aldridge from the University's Zoology department.

'They've tapped into a new food resource and have learned how to feed on fresh water mussels. They swim into the middle of the water, dive down and pull the mussels out.

'The site in March has 50 mussels in a square meter of river bed and each mussel is 10cm long - there's a lot of meat in there. It is a lot of food that they can exploit.'

Residents have reported increased sightings of the rodents, said Dr Aldridge - with one homeowner reportedly shooting 30 rats in his garden.

Rats can spread Wiel's Disease, which can prove fatal within two weeks of infection.

Dr Aldridge believes there are other potential sites around the country where rats have also learned how to do this.

'Mussels are present throughout Britain's waterways. The potential problem is that the rats could spread thoughout the country using these waterways,' he said.

The policy of draining rivers to prevent flooding problems is one possible cause of rats learning about the new food source.

'Levels can get very low and expose the mussels and that's how the rats have discovered them. Brown rats do dive. At this particular spot in March the water would be about 1.5 metres deep in the middle.

'They take one at a time and bring it back to the river bank where they eat it. Each rat has its own pile of mussels,' said Dr Aldridge. 'Rats are very clever.'

The new learning curve also has an ecological impact.

Fresh water mussels help keep the water clean. A marked decline in their numbers would lead to fewer plants, fish and insects.

'Mussels do have natural predators such as mink and ducks, but this is a very much heavier impact than we have had,' said Dr Aldridge.

By Mila Vucevic
University of Cambridge

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