The Spanish slug, in Sweden we call them “the killer slug"

The “Spanish slug” is in Sweden known as the “killer slug” because of the facts that it eats almost everything and also other slugs and even their own species. Their real name is: Arion lusitanicus or Arion vulgarism.

The killer slug has been identified as one of the worst not native invasive species in Europe and it costs millions each year to repair damage and decreased production. In Sweden it has become a pest as an invasive not native species and gardeners spend many hours and money to prevent the slug to destroy their gardens. According to Wikipedia this species isn´t yet established in the USA but it has been seen on the continent and is considered to be a potentially serious threat as an invasive species.

A spanish slug in my garden!
A spanish slug in my garden!
Another one!
Another one!

What is so special about this slug?

In Spain or in Portugal it is probably nothing special about this slug and the Arion lusitanicus are maybe just another slug that can be compared with our native slugs. We have of course native slugs in Sweden too and they can also destroy some plants or vegetables but since they are native they normally have natural enemies. This slug, the Spanish slug, has no or very few natural enemies here. And there are also other causes for their great advance here. When a species immigrate to another country with another type of climate it can either be impossible for them to live in that kind of climate or it can be like heaven for them. Sweden and other countries in northern Europe seem to be a paradise to the Spanish slug. Here the climate is even better for this species than in Spain and Portugal since we have a more humid climate. The only thing that can reduce them seems to be very long and very cold winters with hardly any snow and/or the manual way: to kill them.

How did the Spanish slug end up here in Sweden and northern Europe?

One factor is that we travel more and that our way of living means increased global trade with quick and increased transportation of all kinds of things. All this increase the risk for introduction of invasive foreign species to other countries and new environments. Other reasons for the problem may be the combination with global warming that slowly changes the climate, which can benefit some species. Invasive foreign species can be introduced to new areas unintentional or intentional and it is regarded as on of the biggest threat against the biodiversity. The problems with foreign invasive species can be both ecological and cause retirement or extinction of native species, or genetic by changes in DNA of the native species.

Facts about other foreign species

Foreign Species in Sweden
2 000
Establishes species
1 461
Temporary species
Unknown conditions

Data from report 5910 National strategy and action plan for alien species and genotypes, by the Swedish Environmental Protection Agency.

Of all those species there are luckily only a few that become invasive and the Spanish slug is one of the invasive species.

Other established invasive foreign species:

American comb jelly

American lobster

The Raccoon dog is one species that has been observed and the authorities are now afraid that they are established.

Facts about the Spanish slug

Size 7-15 cm long with grey-brown to red-brown colour and mostly with two characteristic lines on their body. It can be difficult to distinguish the Spanish slug from other slugs. One answer to their thriving is that they are hermaphrodites, which means that they are both male and female and can therefore fertilize themselves. A single slug can produce up to 400 eggs during their lifetime so they can create quite a population by themselves.

They can pass the winter by hiding in garden composts and also in the ground. During relatively warm winters the amount that survives are increasing. They prefer temperatures around 8-10 ° C.

The Spanish slug is not as attractive for carnivores as the native slugs. That is due to that they produce much slime and they are also more leathery than native slugs. This means that the slug have very few enemies. There have been some observations that wild boars, badgers, hedgehogs, Muscovy ducks, and blackbirds eat them. According to Gothenburg’s Natural History Museum 2008 some native helix gastropod and ground beetles eat eggs of the Spanish slug.

Where and how did it come to Sweden?

The Spanish forest slug is native in Spain and Portugal and has been brought here by garden products. Since slugs mostly live in soil and around plants roots they can lay hidden in compost and soil and be transported in that way.

The Spanish slug was first observed in south Sweden in 1975. After entering they spread very quickly and already in 1980 came the first reports of the damage they did.

The reason for their thriving is that they like damp environment as deciduous forest, meadows, parks and gardens. They can now be found in gardens near houses, dishes and even in agriculture environment. The slug has now been observed even in the north parts of Sweden.

Other reasons for their thriving is because they eat native slugs, and they can also fertilize with native slugs and become hybrids. The hybrids are also fertile and there are signs that the hybrids are even more adjusted to the Swedish climate which would mean that they are an even bigger threat.

Since they appear in such big amounts they can destroy some plants completely in an area. They cause severe damage to garden plants and agriculture plants and some vegetables are uneatable because of the slime they leave behind.

Since the slugs are such an annoyance to gardeners it can cause lower house prices in areas where they are in masses. Other problems are nagging damages on vegetables and berries like asparagus and strawberries.

The cause for this big problem is that no one anticipated that a slug could cause this kind of damage. And when it became clear to everyone that it was a major problem no authorities was prepared to take responsibility for the problem.

Now it has gone too far and there is no use to try to control import. The only thing that can be done is to try and prevent the slug to spread to new areas and try to extinct or control the slug in those areas already invaded.

Ways to control the slug or to prevent the slugs to spread any further.

The Swedish Environmental Protection Agency recommend that all garden plants that we buy must be thoroughly examined or that the soil is rinsed away from the roots so that slugs nor their eggs are spread in the garden.

If one wants to have compost in the garden it should be done in closed containers that must be supervised and all slugs in and outside the compost must be extinct as soon as they appear.

Other ways is to put up “slug fences” with electricity around the garden to prevent the slugs to get in.

In agriculture efforts are done by creating a safety zoon of 3-5 metres that is kept dry and well drained since that is one way to decrease the species in that poetically area.

But the most efficient control method is to capture and kill the slugs. This has to be done repeatedly daily and with great patience. Best effect can be seen in areas where all neighbours are active in the slug hunt.

Other ways to fight them is with biologic methods like nematodes that are allowed in Sweden since 2008. The nematode is just possible to use against young slugs. The nematodes intrudes the slug and releases bacteria in the slug that makes the slug stop eating and kills the slug in about two weeks.

The only problem with the nematode is that it isn´t native and it harms also native slugs.

Another possible weapons against the killer slug are to use iron phosphate that makes the slug lose its apatite and slowly dies. The problem with this method is that it is rather expensive since it has to be repeatedly over and over again.

If you want to read more about different ways to control slugs read more here.


All living species on Earth has adjusted and developed in equilibrium with nature over millions of years. Any change has been done over a long period and with tiny steps from generation to generation. Species have been able to reach new land mostly by themselves and natural obstacles like the sea and the mountains have stopped them. But all that have changed and because of it we now face major problems with invasive species that have no natural enemies in the new place they are brought. Natural ecosystems are in danger and the economic costs to repair the damage done by the invasive alien species are massive.

The Spanish slug is just one such species that become an invasive alien species in the wrong environment. It doesn’t matter that slugs are small and pretty harmless species. The damage they cause is gigantic and once an invasive alien species have been established in a new area it is almost impossible to get rid off them! I am afraid that what we now see is the top of an iceberg and there is need for rapid actions and precautions to prevent more alien invasive species.

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Comments 36 comments

Alastar Packer profile image

Alastar Packer 5 years ago from North Carolina

An interesting & well written article with the perspective from Sweden. Over here people used- and maybe still do- salt on the slugs. Thoughtforce, have the Raccoon dogs gone feral? Tack

ahmed.b profile image

ahmed.b 5 years ago from Sweden

Another informative piece of writing by Thoughtforce. Tack för delning.

Trish_M profile image

Trish_M 5 years ago from The English Midlands

Wow! I've never heard of these before. I'll have to check whether they have arrived here in Britain yet :)

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Alistar, many people use salt here as well and it works quite well since the slugs die. The only problem is when the slugs appear in such mass and are everywhere, on patios and on so and around flowers that don't like salt etc. Another factor is that some say it is an unnecessary painful way to kill them and that they suffer before they die. I am nor sure they can feel so much but I have to agree that if one have to kill a living thing it better be quick. But it is a way to control them that works in some cases. Thanks for adding this, I had forgotten about the salt!

Yes, the Raccoon dogs has gone feral and is a real threat. They have been seen in northern Sweden for some time now. But the recent harsh winters and hunt have stopped them from appear in big scale and they are not considered to be established yet. Since 2008 a 100 raccoon dogs have been found in Sweden. They originally come from Asia to Finland and then to Sweden. In Finland they are established so now a cooperation has started among the northern countries in Europe to stop the Raccoon dog. Last fall Raccoon dogs where found in Denmark as well. The way to stop them is to eradicate them. It is all very sad although I cant see any other way for the moment. It is always humans that decide which animal is suited in an area wether it is right or wrong to do so. Thanks for stopping by Alistar and as always leave a great comment.

Take care,


thougtforce profile image

thougtforce 5 years ago from Sweden Author

ahmed.b, Thank you very much for your kind comment and it is nice to see you again! Tina

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Trish M, Yes do that and be prepared if they come! I thought they where already in England, at least in the southern parts. It takes time for them to spread, here they where seen first in the southern parts in 1975 and at first no one understood the danger with them. But for the last ten years they have increased and spread to most parts of the country except for the northern parts where the climate isn't good for them.

Thanks for stopping by and do check your surroundings:) I hope you don't find any.


kashmir56 profile image

kashmir56 5 years ago from Massachusetts

Hi thougtforce, thanks for all this very interesting information on the Spanish slug . I do not like any kind of slug they are just nothing but pest .

Useful and vote up !!!!

AliciaC profile image

AliciaC 5 years ago from British Columbia, Canada

Thank you for the useful information, Tina. The Spanish slug invasion sounds like a serious situation. Invasive species can create so many problems.

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Kashmir, I am glad you found it interesting and I hope you don't have anything like the killers slug in your garden. I cant say I like them either but they have a role to play in the ecosystem. It is the great amount of slugs that is the problem! Thanks for visiting and for your rating:)


thougtforce profile image

thougtforce 5 years ago from Sweden Author

Hi Alicia. Yes it really is a serious situation and I am afraid that the slugs are here to stay. There are so many ways invented to reduce them and to kill them but they seems to thrive anyway despite all our efforts! I suspect they will remain here until the promised climate change occurs! Thanks for your nice comment on this hub since I know you like slugs as well as all living:)


Lauryallan profile image

Lauryallan 5 years ago

I like your hub. I didn't realise slugs could be such a problem.

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Hi Lauryallan, No, neither could we from the beginning. I guess that is why nobody took it serious before it was to late. Who could know that a slug could affect gardeners in this way as well as affect the national economy! It is unbelievable really!

Thanks for your visit here, I appreciate it!


profile image

GianniGreen 5 years ago

I use a new product called the Slug Shield. It is made of copper but expands around the plant as the plant grows. Very effective and last all season. It feels much better to use because it is non-toxic. It is also recommended by the University of California Davis (USA).


Mrs. Menagerie profile image

Mrs. Menagerie 5 years ago from The Zoo

Hi Tina,

Great hub...I had no idea what a big problem these little pests can be. I friend of mine just discoved that her grass is dying because of some sort of slug eating moles that do just as much damage as the slugs themselves. Double trouble!

thougtforce profile image

thougtforce 5 years ago from Sweden Author

GianniGreen, That sounds very interesting, at least for very precious flowers or plants in the garden. I will definitely check it out since non-toxic is always the first choice. Thanks for coming by and for the great tip!


thougtforce profile image

thougtforce 5 years ago from Sweden Author

Mrs. Menagerie, moles can really do much damage in a garden and I am thankful that we don't have that kind of moles here. It really sounds like double trouble! At least the slugs don't turn my garden upside down, they just eat it:) Thanks for coming by and for leaving a both encouraging and comforting comment!


Trish_M profile image

Trish_M 5 years ago from The English Midlands

Hi again :)

I checked Google, and they have been in Britain since 1954, so these could well be the slugs that I constantly find in my garden ~ eating my plants!

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Oh, I am so sorry to hear that Trish M! And they do eat plants! Some plants, like Hosta I have to rescue and replant in pots and let them stand on the balcony so they can recover from the slug attacks! It is horrible. Since 1954, then you have had them for a long time.

If it is the Spanish slug you have in your garden you better keep after them. They increase very rapidly in numbers if the climate is right for them!

Thanks for the info even if it is bad news:)


prasetio30 profile image

prasetio30 5 years ago from malang-indonesia

it looks disgusting. I can say this after saw the picture above. Thanks for writing this and share with us. Tina, you have done a great job here. You got my VOTE as always. Cheers...


D.A.L. profile image

D.A.L. 5 years ago from Lancashire north west England

Hi Tina an excellent hub which deserves all the above accolades. Non-native species are causing problems in eco-systems all over the world. Thank you for sharing. Best wishes to you.

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Prasetio, I must agree with you, even though I respect all living. But these slugs are disgusting. And the amount of them makes it even worse! I will never get use to the daily hunt for these slimy creatures.

Thank you for your nice words and the vote, you are a kind hubfriend and I am delightful for your visit here!

Take care


thougtforce profile image

thougtforce 5 years ago from Sweden Author

Hi D.A.L, I am very glad to see that we haven't lost you completely and that you are here at hubpages again! Yes, it is a big problem with the non-native species and there seems to be very little we can do once they have established in a new place. But I hope we will learn and find a way to stop new species from coming into the country, but with our open borders I have no clue how that should be accomplished.

It is great to see you here and thanks for your comment. I do appreciate it.

Best wishes to you!


MartieCoetser profile image

MartieCoetser 5 years ago from South Africa

This is an excellent article about the Spanish slug, Tina. All slugs give me the creeps, but in particular these killer slugs, devouring even each other. Slugs are also a pest down here. I normally kill them with salt. I’ve experimented during summer – captured one in a glass container. It lived for nine days without food in a fairly dry environment, and I wonder how long he would’ve lived if I did not kill him. My conscience started to bother me because I was torturing him by not allowing him to eat. Oh, will we ever be without pests! I love your new avatar! I’m glad you feel (after many months) comfortable enough here at the hubs to show your face.

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Martie, such an interesting experiment and it is amazing that slug lived for nine days without anything to eat! I guess it was a bit grim but i can understand your motive for doing it:)

No, sadly I believe we have to live with pests and most of them have an important role to play in the ecosystem even if we cant see the use with them. But when they appear in mass and get established in an area without any natural enemies it becomes like a nightmare.

I am sorry to hear you have slugs as pests as well. They must be very good at adapting to new and different areas and have developed a pretty good strategy to survive. Your test in the glass container showed that they can also be without food for many days, no wonder they are increasing! Add to that the ability to be self fertile!

Salt seems to be the weapon that many people use against slugs and it is effective too.

Thanks for your visit Martie, and for your comment. And Yes, I thought it was time, can´t show myself with only a half face for eternety:)

No, joking aside, you are right (of course). I thought why not, nothing bad will happened if I do!

It is always good to see you Martie and your comments are much appreciated by me.


RTalloni profile image

RTalloni 5 years ago from the short journey

Wow, sounds like you have your hands full with an icky problem over there. Reading up on invasive bugs is interesting and at times, surprising.

We have some sort of slug here that we use a combination of weapons to fight. There are times when we absolutely must use a fire ant poison or be overrun with the cruel things, and it takes care of slugs for a good while too. There is a newly introduced fire ant that is yet more vicious starting to spread and here in the south we have a new termite that has been introduced--not very politely either.

If we use the common cornmeal remedy to get rid of ants, we provide fine dining for the slugs so being careful not to feed one pest while fighting another is fine line at times. C'est la vie in this fallen world!

Erin LeFey profile image

Erin LeFey 5 years ago from Maryland

Great article Tina! We have slugs here, but not that kind. Garden creatures always amaze me. The slugs I only see at night, the lizards will come out in the sun. I never realized how destructive they were though, and I guess with them really only coming out at night, most of their predators are asleep! Wonderful research and great pictures. Voted up and useful!

thougtforce profile image

thougtforce 5 years ago from Sweden Author

OH, that sounds like a very difficult situation RTalloni! Fire ants are a serious pest, I have read about them and how vicious they are. In comparison to fire ants and termites I think I prefer slugs:) You are so right in saying that we must be a bit careful not to feed one pest while fighting another. Our way of living influences our world in so many ways and when we try to put things right again we often fail or even make it worse. Every ecosystem is very delicate and are easy to damage permanently. And we seem to understand the damage first when it is too late!

Thanks for reading and for your great input here, it is interesting to know about invasive species in other places.


thougtforce profile image

thougtforce 5 years ago from Sweden Author

Hi Erin! There seems to be garden pests everywhere and since they are everywhere I guess it is us human that do it the wrong way. We try to fight nature as we always do:)

Oh, both slugs and lizards! It sounds very difficult with pests that takes turns and I wonder; do they leave anything behind in your garden?

By writing this hub I have learned that our slugs maybe isn't so bad after all:)They are disgusting and a pest, they are far more than they should bee and they do eat almost everything in a garden if we don't hunt them with all possible weapons, but they are not attacking us and they are hiding during the day:)

Thanks for this interesting and kind comment and the voting!


Julie McM profile image

Julie McM 5 years ago from Southern California

Excellent information about the Spanish slug. We have slugs in our garden. They have been a huge problem in our strawberries. Growing food chemical free does make it difficult to control them. I have discovered that snails and slugs do not like sweet alyssum - they steer clear of it. They also cannot digest oat bran, but they do like to eat it. These methods, along with hand picking are giving us the upper hand.

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Hi Julie McM, I am sorry to hear that you have them too, they seem to be everywhere! Sweet alyssum and oat bran seems like good advices! Yes, we must use several methods at the same time in order to reduce them, that is the only way! Thanks for adding some chemical free tips to beat the slugs, I will try them!

Best wishes


Sunshine625 profile image

Sunshine625 5 years ago from Orlando, FL

Hi Tina, Im looking forward to learning about Sweden through your hubs. I am very impressed with this hub on slugs. We have slugs in Florida but they are just gross insects to us. When I encounter a lazy person I call them a slug. You have taken slug to a whole new level and I'm so impressed. Well done!

Jennifer 5 years ago

I also use slug shields and I love them!

thougtforce profile image

thougtforce 5 years ago from Sweden Author

Hi Sunshine! Yes, this slug is a bit special but I guess that is the case with all foreign and invasive species. Before the Spanish slug came here we just had the common Swedish slugs and they where just ordinary slugs like you describe them. But this one, is totally different. Thank you Sunshine, for your wonderful words!


thougtforce profile image

thougtforce 5 years ago from Sweden Author

Jennifer, slug shields are indeed useful! Thanks for stopping by,


mario 4 years ago

it look like carne asada

thougtforce profile image

thougtforce 4 years ago from Sweden Author

Hi mario, I have never heard that name mentioned in connection with these slugs, but I guess there are many different slugs out there! When I searched for carne asada I got pictures of a mexican dish with roasted meat! I am a bit confused, so I would appreciate if you came back and explained this some more!

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