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The attack of the killer slugs!

Posted by on October 25, 2013

Mark Leach is the membership marketing manager for the Society of Biology, as well as being amateur biologist in residence!

Further to my initial amateur biologist blogs, as my turn on the blogging rota approached I asked my colleague Becky if she had any ideas on where I should focus my quest for knowledge. I really wasn’t expecting the question ‘What do you know about killer slugs?’, and my response (while confirming my amateur biologist status) probably provides a better insight into my DVD watching habits than anything else.

However, as suggested I fired up Google (other web browsers are, of course available!), and discovered that my initial reaction had been way off target! Wikipedia (often a good starting point) revealed that the killer slug, more properly known as Arion vulgaris, (or the Spanish slug to its friends) is a member of the Arionidae (roundback slug) family. Having increased my slug knowledge quite significantly (if you consider ‘those nasty things that ravage our Hellebores and hate salt’ to be knowledge), I read on, to discover that the Spanish slug is a highly invasive breed.

Opinions vary on whether it did indeed originate from Spain, France or Southern England. DAISIE (Delivering Alien Invasive Species Inventories for Europe) lists it among its top 100 invasive species, and I understand it’s the only land gastropod to make the list.

My research then unearthed the SlugWatch website, which provides the discerning slug spotter with all the slug-related resources you can imagine. Their comprehensive section on our Spanish friend explains that the species was first seen in the UK in Spring 2012, and suggests that they may have entered the UK on imported salad leaves, bare root trees or potted plants. They are notable by their voracious appetite, not just limiting themselves to plants, but also tucking into dead animals, and even dog excrement (feel free to join me in a cringe!)

Typically coloured bright orange or reddish brown they breed in a similarly voracious manner, producing more than twice as many eggs as their indigenous counterparts (and it’s additionally worthy of note that they are self-fertilising!), and usurping them from our flower beds, gardens and other areas.  And it seems the situation could worsen. Just when you think you couldn’t love them any more, it appears that they produce massive amounts of mucus (ew!) which deter normal slug predators such as hedgehogs – so they have plenty of time to reach their full size of 8-15 cm, while producing copious amounts of eggs in the process. And they could even (indirectly) cause a hazard to humans as their propensity for eating roadkill has been reported to make roads slippery.

So what can we do in the face of this onslaught?  The SlugWatch website provides instructions on making your own slug traps (although rather less guidance on what to do with a boxful of slugs). They are also encouraging members of the public to report unusual slug sightings to help them to discover as much as possible about the UK slug population, and they also invite you to upload photographs.

So let’s be careful out there!



7 Responses to The attack of the killer slugs!

  1. Mark Leach

    And Sylvia – thanks for the tip – I’ll certainly try that! My Grandad used to swear by beer (as a slug catching method!)

  2. Mark Leach

    Philippa – please tell your children not to panic! I think you can safely reassure them that it’s still safe to play outdoors. I think the ‘killer’ part of the name relates to their eating habits! While they eat all sorts of things, I’ve not been able to find a single online reference that suggests a slug has made off with a child!

  3. Mark Leach

    Hi all – thank you for your comments!
    Firstly Rebecca, I understand from the European Environment Agency’s website ( that the Spanish slug got its name as it is indeed native to the Iberian peninsula – although it seems to travel rather well, and can now be found all over Europe. I’d personally prefer Spain to a British autumn, but there you go…

  4. Sylvia Bickers

    I recently came across a recipe for catching slugs in an old gardening book & it works. Mix bran with methylated spirits to the rate of 1 cup bran to 1 teaspoon meths & mix well. Spread where you know there are slugs. Go out after dark to collect & dispose of. them. They seem to love it, probably makes them drunk!

  5. Philippa

    Hi Mark!

    Why are they called killer slugs? What do they kill? Do they kill people? Should I stop my children playing outside!?


  6. Rebecca Nesbit

    Where’s its native range? Spain?