It was a beautiful morning in the Scilly IslesA group of islands off the coast of Cornwall in south-west England. as the biosecurityMeasures aimed at preventing the spread of harmful organisms. officer made her morning rounds. She had had a wonderful time watching the seabirds. But suddenly she saw something that horrified her. Coming ashore were the birds' greatest enemy: rats!

Rats can be extremely destructive, which is why the British government is spending a lot of money on fighting them.

Storm-petrels, puffins, gannets, terns and razorbills are particularly at risk from rats, which eat their eggs and chicks.

The Scilly Isles are a vital breeding ground for these birds. With the sea to protect them, they ought to be safe - but rats can swim for three days, as well as stow away on boats.

One island saw its number of storm-petrels fall from 20 breeding pairs to five. The rats have now been removed, but great care is needed to stop them coming back.

Some people, though, think we should have more respect for rats. "I do admire rats," says the TV presenter Iolo Williams. "Of all wildlife, they've adapted to live alongside us better than any other animal."

Rats have very good memories. They are also very good at learning, and finding their way around mazes. Experiments at Leuven University in Belgium suggested that rats were actually better than humans at some tests.

The reason, the researchers decided, was that humans always look for rules about how things work - even if there are none. Rats have a simpler approach, but it can be more effective.

And though they are destructive, they cannot really help it. Because their teeth grow around four inches a year, they have to gnawChew. on things to keep them under control.

Humans have not always had a low opinion of them. The Ancient Egyptians and MayansA complex civilisation that lived in modern day Central America from around 2000 BC. Eventually ruined by famine and conflict, the last Maya city was conquered by Spain in 1697. worshipped rats, and the Romans considered them lucky.

Yes: At least in some tests, according to the researchers at Leuven. The fact that there are so many of them shows that they are clever enough to survive and thrive in many different environments.

No: They have very small brains compared to ours, and can only do a limited number of things. They are not about to produce great works of literature or send a rocket into space.

Or... Sometimes not being brilliant is a good thing. If humans had not been so ingenious in inventing machines to exploit fossil fuel, we would not have such huge environmental problems.