A foreign menace is putting every garden in West Norfolk under threat – huge cannibal slugs from Spain that have arrived in force this summer.
The slugs are believed to have slipped into the UK on salad leaves from Europe.
The Arion vulgaris, a new species of which originated in Spain, can grow up to 6in long.
The giants can consume 20 slug pellets before being killed.
Many were spotted in the East of England last summer, but experts hoped the winter frost would kill them off.
But they have returned with a vengeance to vegetable patches and allotments this year
While most reports have been from Norwich or Cambridge, there have been reports in West Norfolk.
Bug expert Dr Ian Bedford, head of entomology at the John Innes Centre in Norwich, said he had received a report from one gardener in Hunstanton.
He said he has seen them chomping on dead animals including mice and even dog poo.
Dr Bedford also worries the Spanish slugs could breed with native species producing a “hybrid” that could survive the harsher British winters.
He said: “Following the really bad outbreak in 2012 we expected it to be just as bad in 2013 but the late frost wiped out some of the juveniles.
“The very mild winter we had last year enabled the adults to survive so this year we have had quite a few reports of people with several hundred in their garden.”
He said: “The grey field slug does cause problems but that can be controlled. But with the Spanish slugs when the conditions are right we don’t really have any way we can control it effectively.
“If you leave them, they produce more eggs than our native slugs and they could swamp them. They also carry parasites heartworm and microsporidia, which could affect other animals.”
Dr Bedford said he believed that the slug uses water courses to spread so rapidly around the country. He said: “We need to do more research to be sure where it is and how much damage it’s causing.”