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• Aggressive crop pest slug species is identified in the UK for the first time
• Concern about potential effects on food crops and biodiversity as seen in other countries

• Researchers from the John Innes Centre and UK universities prepare a research plan to investigate and tackle the problem

When Ian Bedford noticed an unusually high number of slugs in his garden this spring he didn't realise he had stumbled on a foreign invasion.

The large brown slugs seemed to have appeared from nowhere and were eating almost everything in their path.


Dr Bedford, head of the BBSRC-funded John Innes Centre's (JIC) Entomology facility, was intrigued by the high number and aggressiveness of the slugs and decided to investigate.

He said: "In early spring I saw absolutely massive numbers of this brown species in the garden. It got to the point where you'd walk down into the garden and you could easily count 50 to 100 slugs on the lawn, so I was very interested to see what was going on.

"And then I noticed that it wasn't just plants that were being attacked by this species, they were actually eating things like dead animals, there was an instance of a mouse that was killed by my cat, slugs were swarming over it and eating it. They were also eating other slugs, eating snails, even eating shells."

Fortunately in his role at the JIC, an international centre of excellence in plant science and microbiology, Dr Bedford had an eye out for potential crop pests in the UK.

He resolved to find out what this slug was, suspecting it could be a foreign species called the Spanish Slug (Arion vulgaris) which has become a problem in northern mainland Europe in recent years, and has been nicknamed the 'killer slug' for its cannibalistic tendencies.

He said: "I heard on the TV that Dr Les Noble from Aberdeen University was interested in what was happening with slugs in the UK this year. He was saying there were large numbers and he thought it was down to the unusually wet weather we'd had this year, promoting the population increase of a species called Arion flagellus, which is commonly known as the Spanish Stealth Slug.

"But what was happening here was slightly different to what was recorded for Arion flagellus and was similar to what had happened in Europe, where a species commonly known as just the Spanish Slug, Arion vulgaris, had moved into Scandinavia and absolutely decimated crops in huge numbers. There were even instances of cars having crashes because slugs had been eating road-kill and made the roads slippery.

"So I contacted Les and we sent him some specimens. He had them identified and confirmed that this was Arion vulgaris and it was the first time it had been identified in the UK. This part of UK seems to be like an open door to all sorts of invasive species. I don't know if it's because we've got a number of ports here."

The presence of this aggressive species is bad news. With few predators, a voracious appetite and the ability to lay around 400 eggs each, the slugs multiply quickly, can cause huge damage to crops and can push out other slugs and snails to dominate an area.

Dr Bedford said: "It's obviously of great concern that we now have this species here. There's been lots of reports from around the county of massive problems with slugs which I'm sure are now going to be Arion vulgaris.

"We had a meeting here recently with Les Noble and Dr Gordon Port (from Newcastle University), to discuss the possibility of getting some funding to look at this further. We want to look at the environmental impact because we know that where this slug appeared in northern Europe, other indigenous species disappeared. I haven't seen any other species here since probably May time."

Dr Bedford and his colleagues at Aberdeen University and Newcastle University are developing a potential programme of research to find out more about the Spanish Slug, its distribution in the UK and the effects it is having.

He said: "We're very interested in seeing what is actually happening, do these invasive species come in with parasites that kill off similar species but not actually kill off their original host? We don't know, so we're going to be looking at this.

"When these slugs invade, do they actually interbreed with indigenous species, are there hybrids out there? We want to see what sort of funding we can get and utilise Norwich's The Genome Analysis Centre (TGAC) to try and do some genomics on the population of slugs and see what's happening."

If suspicions about the Spanish Slug are right then the UK could see a population explosion in spring when their buried eggs will hatch. If so now is the right time for the collaborative team to start planning how to tackle the potential problem.

"I think the main thing is people are going to see humungous amounts of slugs in their gardens," said Dr Bedford. "There are reports of oilseed rape having problems this year from molluscs which we think could well be because of this Spanish Slug. I've actually seen them in a potato field in the middle of summer sliming across dry, sandy soil and the agronomist with me couldn't believe what he was seeing because slugs don't usually do that. It's a hardy species."