Meet the Spanish ‘Killer’ Slug that Could Ravage British Crops

British crops may soon be under attack from the marauding Spanish slug, invaders whose nibbling through plants, crops and even a dead animal or two cannot be stopped by conventional control measures. So alarmed are UK scientists by the threat of the species, they’ve now put out a nationwide call for public assistance in counting Spanish slugs.

First spotted in the UK in East Anglia in January of 2012, the Spanish slug is causing growing concern because it is resistant to many control measures such as standard slug pellets. Add to that the Spanish slug is capable of breeding at a much faster rate than the native species and that it eats crops and fruits that Britain’s own slugs don’t touch, and scientists feel justified in ringing the alarm bells.

Keith Norman, of farming company Velcourt, told the BBC that the Spanish slug  really does pose a significant problem for UK farmers, saying:

“It is a disaster waiting to happen if the Spanish slug proliferates and establishes itself in the UK,” said Mr Norman. ”The Spanish slug causes more eating damage and cannot be controlled with existing measures.”

The Spanish slug is already known to have spread across areas of Northern Europe and is thought to have been at least partially responsible for a severe crop failure that occurred in Scandinavia. Its slightly more placid cousin, the Spanish Stealth slug (Arion flagellus), is already well established in the UK, having been introduced in the 1950s, but this is the first time the Spanish slug (Arion vulgaris) has really got a foothold. It’s believed it may have entered the UK via improperly screened produce, most likely salad leaves.

As a sidenote, the Spanish slug has not been recorded in the USA but is treated as a serious invasive species risk and it has been recommended it be given top quarantine status, perhaps demonstrating how potentially serious the issue is.

The omnivore is sometimes referred to as the “killer slug” due to its taste for sampling the dead of its own kind — or any kind as it has been known to eat roadkill — and also excrement, potentially posing a health risk should children encounter the slug in the garden.

The main fear for scientists in the UK is that this invasive species could breed with Britain’s own slug population, thereby risking a mix of the Spanish slug’s own resistance to drier conditions with the native species’ ability to stand cold and damp conditions. This has already occurred in some other parts of North Europe where the slug has interbred with the more winter-hardy black slug. What that could add up to, scientists say, is a gastropod that is even more effective at ravaging garden plants and crops. So what can be done?

Send in the 17-Year-Old Slug Scientist

Jumping into action, a 17-year-old student called Rachel Ayers from Notre Dame High School in Norwich has helped a team of Norwich-based scientists to set up a dedicated website called SlugWatch, where slug sleuths the length and breadth of the UK can log on to find out more about the Spanish slug, and also report sightings. The aim of the website is to get an idea of the Spanish slug and all slug population numbers and, crucially, whether the Spanish slug appears to be breeding.

Ayers has also helped design special cards — a slugs top trumps game — that depict the main characteristics of Britain’s 30 different slug species and, crucially, the Spanish slug’s own giveaway characteristics. These cards will be used in schools to help kids get involved in the slug sleuthing.

“We want people to survey their gardens, local areas and school grounds for slugs, or they can build a trap using instructions on the site,” Ayers is quoted as saying. “One of the most interesting parts of the project was learning about slugs and how to identify them.”

The Spanish slug can be identified by its quite distinct reddish brown color. The species also grows to between 8cm and 15cm and so their size may also be a clue to whether the species has invaded a garden near you. More tips on identifying the species can be found on the SlugWatch website.

Count, Don’t Kill

It should be pointed out that while the invasive Spanish slug is thought to pose a significant problem if its numbers do get out of control, no one is advocating a mass cull of the slug.

Another thing is that slugs do in fact serve a vital function in our ecosystem: composting comes naturally to slugs who break down vegetation and therein provide food for a number of other critters including hedgehogs, birds and toads.

Through the SlugWatch drive, it is hoped that people will learn more not just about the Spanish slug, but also Britain’s native species, including the common garden slug, the large black slug and the keel slug, among many others, and that perhaps they might learn to think of slugs not just as potential plant wrecking pests but as a diverse number of species — only a few of which pose a problem.

What action to curtail Spanish slug numbers will ultimately prove appropriate is as yet unknown. In the meantime though, the chance at educating children and adults alike is a positive and something for which we can thank the invading Spanish “killer” slug.

Photo credit: Thinkstock.


Carrie-Anne Brown

thanks for sharing :)

Pushpraj Singh
Pushpraj Singh4 years ago

I say cull on.

Ruby W.
Inez w4 years ago

Cathleen K.
This country is doing enough culling at present, what with the badgers being culled in two separate pilot areas due to BOVINE tb and deer (in a sanctuary as well, people trying to tempt the glorious male deers out of said sanctuary so that the deer hunters can try and kill them (See Big Red the deer at League Against Cruel Sports for further info on this)) and also a backdoor repeal of the hunting with dogs ban on the cards.
Although a slug may be insignificant to yourself, to people like me, a Buddhist, it is important that no living being is harmed or killed. It is great that some people are looking into the science behind these slugs, is it a case that many more slugs are here than we first thought, or is it a case that there are only a handful. Get the science first and then figure out what to do second.
Destroy a part of an ecology and there may be no going back

Karen F,
whilst you are correct about the badgers, no one is culling hedgehogs in the UK. The numbers are falling dramatically due to weather, loss of hedgerows and habitat and roads going through their habitat so they get hit and killed that way. No one is going out to purposely catch and kill the little guys though

Ruhee B.
Ruhee B4 years ago

It's not good for hedgehogs to eat slugs as slugs often carry lungworm which will infect the animal who eats it. I don't like slugs but hopefully they can be controlled in some way other than killing them!

Kate Raymond
Past Member 4 years ago

This may be a problem, but all that extra food has to be good for hedgehogs!

Lynn C.
Lynn C4 years ago

So glad they're not advocating killing as a 'remedy'. Not that it's not necessary in some cases, but I think it should always be a survival issue and the last resort.

Cathleen K.
Cathleen K4 years ago

Count but don't cull? Why? It's an invasive species that's known to be massively destructive and capable of crossbreeding with natives to aid it's adaptation to a cooler, wetter climate. Get your head out of your arse, Britain.

Dimitris Dallis
Past Member 4 years ago

Thanks for sharing.

Carole R.
Carole R4 years ago

Thank you for the post.

Dani C.
Dani C4 years ago

thanks...wouldnt want to find these critters in my salad