It sounds like the stuff of nightmares – giant earthworms that, if left alone, keep growing and growing to the size of a baby snake.
But this is no bad dream – scientists working on the Isle of Rum, off the coast of Scotland, have found the biggest specimens ever seen in the UK, more than three times the length and weight of a normal worm.
The exceptionally large invertebrates measure up 40 cm (1.3 ft) long, having blossomed due to rich soil and a lack of predators. They’re similar in size to a newly-hatched adder.
In an interview on the BBC Radio 4 Today programme, Dr Kevin Butt, lead researcher on the earthworm study, carried out by the University of Central Lancashire, said: “These things weigh about twelve and a half grams – but the normal size for these things is about four to five grams.”
He agreed with presenter John Humphrys that the whole thing is “slightly spooky”.
The worms, Latin name Lumbricus terrestris, were found at Papadil, an abandoned settlement on Rum, which is home to a tiny population of around 30 people.
“When these things came out of their burrows they were like small snakes,” he said.
However, far from being the stuff of nightmares, Dr Butt told the Telegraph the existence of the worms was “a delight” to discover as they are crucial to the ecosystem, and help lessen the risk of flooding.
“Without their activities we’d be a lot worse off. They’re just as important as bees are in pollinating plants. They help aerate the soil and drain away water and stop surface erosion,” he explained.
Dr Butt believes the Rum worms are bigger than average due to their remote, undisturbed location, with good quality soil.
Rum also lacks predators such as badgers, moles, hedgehogs and foxes which would usually gobble the worms before they had chance to grow into monsters.
Unlike most animals, which stop growing once they reach an adult size, earthworms keep on growing if left alone.
“These things have just have been left and have grown bigger and bigger,” explained Dr Butt, who has been studying earthworms for around 30 years.
Asked if an enthusiastic schoolboy might be able to achieve a similarly giant specimen by looking after it at home, he confirmed this is possible.
“In the laboratory we can keep them and feed them well and in a matter of a couple of years you can grow them to 15, even 20 grams,” he said.
However, those spooked by the idea of giant worms have little to fear if they visit Rum.
“If they feel footsteps they will just go down deeper into the earth. They’re not going to jump out and grab people,” he said.
News of the Papadil worms is contained in a paper recently published in The Glasgow Naturalist journal.