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New study finds Britain crawling with extra slug species

Slugs from France, Spain and Italy are invading Britain

A new study undertaken by scientists from Amgueddfa Cymru – National Museum Wales, published this week in the scientific journal PLOS One, shows that Britain is crawling with 20% more species of slugs than ever before. Most are already widespread, and may pose new threats to gardeners and agriculture.

Most of the 8 extra slug species probably come from continental Europe, from Spain, France, Italy, Bulgaria or Ukraine. They were found in habitats from gardens to woodlands and feed upon shoots, roots and even earthworms. (Scroll down to Notes to Editors for a full list of the new slugs)


The study was led by zoologist Dr Ben Rowson from Amgueddfa Cymru – National Museum Wales together with Bill Symondson from Cardiff University and Roy Anderson from the Conchological Society. They made the discoveries when collecting slugs from habitats across Britain and Ireland, to produce a new comprehensive 140 page identification guidebook published this month by the Field Studies Council. The work was funded by a research project grant from the Leverhulme Trust. The scientists used DNA, anatomical techniques and digital photography to check each slug’s identity and ensure the guide was accurate.


Dr Rowson said, “We had the know-how to find all 36 known slug species, some of which are quite rare, but were amazed to encounter so many species we didn’t recognise. Some were obvious at first glance, but others were more subtle and only through further analysis we could be sure they were different.”


The two-year study compared DNA sequences from hundreds of newly-collected slugs with existing data from Europe, and indicated that each extra species was as genetically distinct as the others in its group. In most cases the animals clearly differed in their appearance or anatomy as well. The records suggest most of the species are already established in numerous places, and the researchers believe each is either recently introduced or has simply been overlooked.


Dr Rowson continued, “We found one small potato-eating species (Tandonia cf. cristata) in allotments in Wales, a churchyard in western Ireland, and waste ground on the Isle of Wight. It seems to have been introduced from Bulgaria or Ukraine, and has already bred and been spread around unnoticed. Worries about slugs rise and fall with the seasons or weather, but to find all these extra species lurking here is a real concern.”


British slugs have been in the news in recent years, with species such as the carnivorous Ghost Slug, the Spanish Stealth Slug (Arion flagellus) and the notorious Spanish Slug (Arion vulgaris) making headlines. But the 8 extra species are a bigger revelation.


The brand new guidebook will feature photographs of all British and Irish slugs, some of which are surprisingly attractive and not all of which are pests. However, Dr. Rowson and the team are still uncertain of the identity and origins of some of the extra species. Some may even be new to science, there being several parts of Europe where undescribed slug species are thought to occur.


Amgueddfa Cymru operates seven national museums across Wales. These are National Museum Cardiff, St Fagans: National History Museum, National Roman Legion Museum, Caerleon, Big Pit: National Coal Museum, Blaenafon, National Wool Museum, Dre-fach Felindre, National Slate Museum, Llanberis and the National Waterfront Museum, Swansea.


Admission to all Amgueddfa Cymru – National Museum sites is free, thanks to the support of the Welsh Government.




For further information, images or interview opportunities with Ben Rowson, please contact Lleucu Cooke, Communications Officer on (029) 2057 3175 or email


Notes to Editors


Link to the PLOS One paper:


The eight extra species of slug


1.       Arion cf. vulgaris              

2.       Arion cf. empiricorum

3.       Arion cf. iratii

4.       Arion cf. fagophilus

5.       Tandonia cf. cristata

6.       Testacella cf. scutulum

7.       Limax cf. dacampi

8.       Deroceras panormitanum  


Two large, warty species of round-backed slug (1 & 2) were found in the east of England. They are probably of French origin, and may become plant pests like Arion vulgaris, with which they were sometimes found. Species in the round-backed slug family can be very difficult to distinguish.


Two smaller species in this family (3 & 4) were found only in woodlands in South Wales, and are most closely related to slugs from the Pyrenees of Spain and France.


Two very different soil-dwelling slugs have already become widespread in British garden and allotment soils. One is a root-eating slug (5) normally found from Bulgaria to Ukraine, and is a potential pest of potatoes and carrots. The other is an earthworm-eating shelled slug (6), a member of a carnivorous slug family.


Finally, two species of short-keeled slugs are probably relatively recent imports from Italy. One, found in Yorkshire, is enormous at up to 15 cm long (7) but seems to be found only at one site. The other, found in Cardiff, is much smaller at up to 3.5 cm long (8). It is a close relative of the Tramp Slug Deroceras invadens, a species that has been spread all around the world.


The title of the paper in PLOS One is ‘The Slugs of Britain and Ireland: Undetected and Undescribed Species Increase a Well-studied, Economically Important Fauna by More Than 20%’.


The Leverhulme Trust was established by the Will of William Hesketh Lever, the founder of Lever Brothers. Since 1925 the Trust has provided grants and scholarships research and education. Today, it is one of the largest all-subject providers of research funding in the UK, distributing over £60m a year. For more information about the Trust, please visit