{{Short description|Species of gastropod}} {{subspeciesbox | image = Red Slug in Marburg Hessen Germany.jpg | status = LC | status_system = IUCN3.1 | status_ref = <ref>{{cite iucn|author=Rowson, B.|year=2017|title=''Arion rufus''|article-number=e.T171016A1320066|doi=10.2305/IUCN.UK.2017-3.RLTS.T171016A1320066.en|access-date=29 March 2024}}</ref> | status2 = G4 | status2_system = TNC | status2_ref = <ref name=NS>{{cite NatureServe |id=2.116913 |title=''Arion rufus'' |access-date=7 May 2026}}</ref> | genus = Arion | species = ater | subspecies = rufus | authority = (Linnaeus, 1758) | synonyms = * ''Arion (Arion) rufus'' <small>(Linnaeus, 1758)</small> superseded rank * ''Arion (Lochea) rufus'' <small>(Linnaeus, 1758)</small> superseded combination * ''Arion (Lochea) rufus var. miniaceus'' <small>Mabille, 1871</small> junior subjective synonym * ''Arion rufus'' <small>(Linnaeus, 1758)</small> superseded rank * ''Arion rufus rufus'' <small>(Linnaeus, 1758)</small> * ''Limax rufus'' <small>Linnaeus, 1758</small> superseded combination }}
'''''Arion ater rufus''''', also known as the '''red slug''', '''large red slug''',<ref name=ire>[http://www.habitas.org.uk/molluscireland/species.asp?ID=23 ''Arion'' (''Arion'') ''rufus'' (Linnaeus 1758), Large red slug] MolluscIreland. National Museums Northern Ireland. 2010.</ref> '''chocolate arion'''<ref>[https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=77078 ''Arion rufus''.] Integrated Taxonomic Information System (ITIS).</ref> and '''European red slug''',<ref name=ro>Rosetta, R. [http://oregonstate.edu/Dept/nurspest/Europeanredslug.htm European red slug.] Pacific Northwest Nursery IPM. Oregon State University.</ref> is a subspecies of land slug in the family Arionidae, the roundback slugs.<ref name="WoRMS">{{WRMS species|1741443|''Arion ater rufus'' (Linnaeus, 1758)|1 November 2025}}</ref>
==Description== [[File:Arion ater & rufus.jpg|thumb|left|Black slug (''Arion ater'') and Red slug.]] Slugs in the genus ''Arion'' have the pneumostome (respiratory pore) in the front part of the mantle and a round back without a keel. ''Arion ater rufus'' is one of the largest species in the genus, up to 150 mm extended. As an adult it lacks the lateral bands found in many smaller congeners, but in some forms the sides are paler than the back. The body colour is often reddish, sometimes vividly so, but orange, yellowish, brown and greyish forms are also usual, and some individuals may be black. The foot fringe is vertically striped and is often a different colour than the back. The head and tentacles are often darker than the rest of the body. The mucus is sticky and colourless or orange. Externally the species is not reliably distinguishable from several other species, including ''A. ater'' and ''A. vulgaris'', and can be difficult to distinguish from less closely related species such as ''A. flagellus'', especially in the Iberian Peninsula where further similar species exist.<ref name="Wiese2014">{{cite book |last1=Wiese |first1=V. |title=Die Landschnecken Deutschlands |date=2014 |publisher=Quelle & Meyer |location=Wiebelsheim |isbn=978-3-494-01551-4}}</ref><ref name="Rowson2014b">{{cite book |last1=Rowson |first1=B. |last2=Turner |first2=J. |last3=Anderson |first3=R. |last4=Symondson |first4=B. |title=Slugs of Britain and Ireland: identification, understanding and control |date=2014 |publisher=FSC |location=Telford |isbn=978-1-908819-13-0}}</ref><ref name="Welter-Schultes2012"/>
Eggs are typically about 5 mm in diameter, slightly ovoid. They are opaque white, because of a calcareous layer in the shell.<ref name="Rowson2014b"/> Juveniles often have lateral bands.<ref name="Rowson2014b"/>
Adult ''A. ater rufus'' and ''A. ater'' are straightforward to distinguish from ''A. vulgaris'' and ''A. flagellus'' by dissection; in the former pair the oviduct is thinner because the ligula is positioned in the upper atrium, not the oviduct. The anatomical differences between ''A. ater rufus'' and ''A. ater'' are more subtle: the latter tends to have a larger lower atrium, and its ligula differs (e.g. bowl-shaped rather than C-shaped).<ref name="Reise2020"/>
''Arion ater rufus'' will often rock spectacularly from side to side when irritated, which is useful to distinguish it from ''A. flagellus'' and generally from ''A. vulgaris'', but not from ''A. ater''.<ref name="Rowson2014b"/>
==Taxonomy== Linnaeus described ''A. ater rufus'' together with ''Arion ater'' in 1758.<ref name="Linn1758">{{cite book |last1=Linnæus |first1=C. |title=Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata. |date=1758 |publisher=Salvius |location=Holmiæ |page=652 |doi=10.5962/bhl.title.542 |hdl=10366/131929 |url=https://www.biodiversitylibrary.org/bibliography/542 }}</ref> His description consisted mainly of references to earlier published descriptions from around Europe.<ref name="Altena1963">{{cite journal |last1=Regteren Altena |first1=C.O. van |title=Notes sur les limaces. 8. Sur l'état de deux espèces nominales du genre ''Arion'' |journal=Basteria |date=1963 |volume=27 |pages=1–6}}</ref> Recently a lectotype for ''A. rufus'' has been designated from amongst the specimens to which Linnaeus indirectly referred.<ref name="Reise2020">{{cite journal |last1=Reise |first1=H. |last2=Schwarzer |first2=A.-K. |last3=Hutchinson |first3=J.M.C. |last4=Schlitt |first4=B. |title=Genital morphology differentiates three subspecies of the terrestrial slug ''Arion ater'' (Linnaeus, 1758) s.l. and reveals a continuum of intermediates with the invasive ''A. vulgaris'' Moquin-Tandon, 1855 |journal=Folia Malacologica |date=2020 |volume=28 |issue=1 |pages=1–34 |doi=10.12657/folmal.028.001|doi-access=free }}</ref> This is a non-surviving specimen amongst those that Martin Lister described from Almondbury in West Yorkshire, England.<ref name="Lister1685">{{cite book |last1=Lister |first1=M. |title=Appendicis ad historiæ animalium Angliæ, tres tractatus, &c. Altera editiio, auctior & emendatior |date=1685 |publisher=Smith |location=Londini}}</ref>
''Arion ater rufus'' can be externally indistinguishable from ''Arion ater''.<ref name="Boettger1949">{{cite journal |last1=Boettger |first1=C.R. |title=Zur Kenntnis der großen Wegschnecken (''Arion'' s. str.) Deutschlands |journal=Archiv für Molluskenkunde |date=1949 |volume=78 |pages=169–186}}</ref> There are anatomical differences between the taxa in their genitalia, but they hybridise,<ref name="Evans1986">{{cite journal |last1=Evans |first1=N.J. |title=An investigation of the status of the terrestrial slugs ''Arion ater ater'' (L.) and ''Arion ater rufus'' (L.) (Mollusca, Gastropoda, Pulmonata) in Britain |journal=Zoologica Scripta |date=1986 |volume=15 |issue=4 |pages=313–322 |doi=10.1111/j.1463-6409.1986.tb00232.x|s2cid=84998531 }}</ref><ref name="Hatteland2015">{{cite journal |last1=Hatteland |first1=B.A. |last2=Solhøy |first2=T. |last3=Schander |first3=C. |last4=Skage |first4=M. |last5=Proschwitz |first5=T. von |last6=Noble |first6=L.R. |title=Introgression and differentiation of the invasive slug ''Arion vulgaris'' from native ''A. ater'' |journal=Malacologia |date=2015 |volume=58 |issue=1–2 |pages=303–321 |doi=10.4002/040.058.0210|s2cid=84108976 }}</ref> and so they have often been considered conspecific, particularly by British authors.<ref name="Kerney1999">{{cite book |last1=Kerney |first1=M. |title=Atlas of the land and freshwater molluscs of Britain and Ireland |date=1999 |publisher=Harley Books |location=Great Horkesley}}</ref><ref name="Reise2020"/> The appropriate name is then ''Arion ater rufus'' (i.e. a subspecies of ''A. ater''), following the decision of Fleming ("the first reviser", in 1822) to give ''A. ater'' precedence over ''A. rufus''.<ref name="Fleming">{{cite book |last1=Fleming |first1=J. |editor1-last=Napier |editor1-first=M. |title=Supplement to the fourth, fifth and sixth editions of the Encyclopædia Britannica with preliminary dissertations on the history of sciences. Vol. 5 . |date=1822 |publisher=Constable |location=Edinburgh |pages=567–584 |chapter=Mollusca}}</ref><ref name="Reise2020"/>
Differences in mitochondrial DNA and minor anatomical differences exist between populations of ''A. rufus'' found in the British Isles and the commonest form found on the European continent.<ref name="Chevallier1974">{{cite book |last1=Chevallier |first1=H. |title=Les grands ''Arion'' de France (Mollusca, Pulmonata). Taxonomie, biogeographie, écologie, polymorphisme, croissance et cycle biologique |date=1974 |publisher=Ph. D. Thesis, Université de Paris}}</ref><ref name="Rowson2014a">{{cite journal |last1=Rowson |first1=B. |last2=Anderson |first2=R. |last3=Turner |first3=J.A. |last4=Symondson |first4=W.O.C. |title=The slugs of Britain and Ireland: undetected and undescribed species increase a well-studied, economically important fauna by more than 20% |journal=PLOS ONE |date=2014 |volume=9 |issue=3 |article-number=e91907 |doi=10.1371/journal.pone.0091907|pmid=24740519 |pmc=3989179 |bibcode=2014PLoSO...991907R |doi-access=free }}</ref><ref name="Reise2020"/> These have been given the status of species or subspecies. Because of the designation of the lectotype, the name ''rufus'' now refers to the British form, which may be called ''Arion ater rufus'' depending on which taxa are considered as species or subspecies. Garsault (1764)<ref name="Garsault1764">{{cite book |last1=Garsault |first1=F. A. P. de |title=Les figures des plantes et animaux d'usage en medecine, décrits dans la Matiere Medicale de Mr. Geoffroy medecin, dessinés d'après nature par Mr. de Garsault, gravés par Mrs. Defehrt, Prevost, Duflos, Martinet &c. Niquet scrip. Vol. 5 |date=1764 |location=Paris |doi=10.5962/bhl.title.49481 |url=https://www.biodiversitylibrary.org/item/104537 }}</ref> appears to have been the first to describe the Continental form under a name other than ''rufus'', so its name should be ''Arion ruber'', ''Arion rufus ruber'' or ''Arion ater ruber''.<ref name="Reise2020"/> Quite possibly there are further forms of similar status from elsewhere in France and Spain.
==Distribution== ''Arion ater rufus'' is widespread in western Europe, including France, the Low Countries, Germany, western Poland, Switzerland and the southern parts of the British Isles.<ref name="Welter-Schultes2012">{{cite book |last1=Welter-Schultes |first1=F.W. |title=European non-marine molluscs, a guide for species identification |date=2012 |publisher=Planet Poster Editions |location=Göttingen}}</ref> In Scandinavia and northern Britain the closely related species ''A. ater'' occurs in its place, but ''A. rufus'' has invaded parts of Scandinavia over the last 200 years.<ref name="Proschwitz1985">{{cite journal |last1=Proschwitz |first1=T. von |title=Röda skogssnigeln ''Arion rufus'' (L.), en mellaneuropeisk art stadd i snabb spridning med människan i Sverige |journal=Fauna och Flora |date=1985 |volume=80 |pages=121–138}}</ref> It is also extending its range further eastward in Europe,<ref name="Soroka2009">{{cite journal |last1=Soroka |first1=M. |last2=Kozłowski |first2=J. |last3=Wiktor |first3=A. |last4=Kałuski |first4=T. |title=Distribution and genetic diversity of the terrestrial slugs ''Arion lusitanicus'' Mabille, 1868 and ''Arion rufus'' (Linnaeus, 1758) in Poland based on mitochondrial DNA |journal=Folia Biologica (Kraków) |date=2009 |volume=57 |issue=1–2 |pages=71–81|doi=10.3409/fb57_1-2.71-81 |pmid=19459464 }}</ref> and even in eastern Germany it is possibly an old introduction.<ref name="Reise2020"/> Its status in Spain is uncertain because of the presence there of other similar species.<ref name="Castillejo2019">{{cite journal |last1=Castillejo |first1=J. |last2=Rodríguez-Castro |first2=J. |last3=Iglesias-Piñeiro |first3=J. |title=J., J., J.Estudio comparativo de la anatomía y caracterización del ADN de los ariónidos descritos por Torres Mínguez (1925) en Cantabria (España): ''Arion cendreroi'' y ''A. fulvipes'', y la de ''A. rufus'' y ''A. vulgaris'' (Gastropoda Pulmonata: Arionidae) |journal=Spira |date=2019 |volume=7 |pages=49–69}}</ref> ''Arion ater rufus'' is also known as an introduction in North America.<ref name="Zemanova2018">{{cite journal |last1=Zemanova |first1=M.A. |last2=Broennimann |first2=O. |last3=Guisan |first3=A. |last4=Knop |first4=E. |last5=Heckel |first5=G. |title=Slimy invasion: climatic niche and current and future biogeography of ''Arion'' slug invaders |journal=Diversity and Distributions |date=2018 |volume=2018 |issue=11 |pages=1627–1640 |doi=10.1111/ddi.12789|bibcode=2018DivDi..24.1627Z |doi-access=free }}</ref> A related form, reddish in coloration but perhaps more closely related to ''A. ater'' s.s., has recently turned up in Turkey, on both sides of the Bosphorus.<ref name="Reise2018">{{cite journal |last1=Reise |first1=H. |last2=Arslangündoğdu |first2=Z. |last3=Schlitt |first3=B. |last4=Hutchinson |first4=J.M.C. |last5=Hızal |first5=E. |last6=Bacack |first6=E. |title=H. Reise, ZFirst records of the terrestrial slug ''Arion ater'' s.l. (Linnaeus, 1758) (Pulmonata: Arionidae) from Turkey |journal=Folia Malacologica |date=2018 |volume=26 |pages=213–220|doi=10.12657/folmal.026.024 |doi-access=free }}</ref>
==Habitat== It is familiar from gardens and parks as well as disturbed agricultural landscapes, but also from a diversity of natural habitats including woodland, meadows, margins of water bodies, coastal habitat, and moorland.<ref name="Rowson2014b"/><ref name="Welter-Schultes2012"/> However, in much of its range ''A. rufus'' has declined dramatically over the last decades due to replacement by the externally similar ''Arion vulgaris''.<ref name="Kappes2009">{{cite journal |last1=Kappes |first1=H. |last2=Kobialka |first2=H. |title=Die Nacktschneckengesellschaften in NW-Deutschland (Gastropoda: Milacidae, Boettgerillidae, Limacidae, Agriolimacidae, Arionidae): ein Ergebnis der NRW-Kartierung |journal=Natur und Heimat |date=2009 |volume=69 |pages=73–94}}</ref><ref name="Zemanova2017">{{cite journal |last1=Zemanova |first1=M.A. |last2=Knop |first2=E. |last3=Heckel |first3=G. |title=Introgressive replacement of natives by invading ''Arion'' pest slugs |journal=Scientific Reports |date=2017 |volume=7 |issue=41908 |page=14908 |doi=10.1038/s41598-017-14619-y|pmid=29097725 |pmc=5668256 |bibcode=2017NatSR...714908Z |doi-access=free }}</ref><ref name="Reise2020"/>
==Life cycle== The species is adult in summer, although the timings vary by a month or so between localities. Typical would be for some individuals to reach adult size in May, but to mature only in July, with some surviving until October. The eggs hatch over a broad period from late autumn to spring and studies find great variation in growth rate. Adults are on average over 300 times the mass of hatchlings. The life cycle is predominantly annual; but possibly a few late hatchlings overwinter as juveniles and mature only 18 months or so after hatching.<ref name="Hutchinson2017">{{cite journal |last1=Hutchinson |first1=J.M.C. |last2=Reise |first2=H. |last3=Skujienė |first3=G. |title=Life cycles and adult sizes of five co-occurring species of Arion slugs |journal=Journal of Molluscan Studies |date=2017 |volume=83 |issue=1 |pages=88–105 |doi=10.1093/mollus/eyw042|doi-access=free }}</ref>
==Behavior== At rest ''A. rufus'' contracts into a hemispherical shape. When disturbed, it performs a rocking motion, sometimes for many minutes.<ref name="Rowson2014b"/> Although predominantly nocturnal, rain brings it out during daylight. It is an omnivore.<ref name="Rowson2014b"/>
''Arion ater rufus'' is hermaphrodite and during its mating spermatophores are swapped reciprocally. Mating typically starts with one slug following the other, periodically nibbling its tail. When the leading slug doubles back, they may form a wheel configuration circling clockwise, with each nibbling the other. This soon evolves into the yin-yang configuration (or the wheel step may be skipped), with each animal hooked around the other, their genital pores pressed together, the configuration no longer rotating.<ref name="Dreijers2013"/> The genitalia take some minutes to engage and evert, the epiphallus (spermatophore producing organ) connecting to the bursa trunk of the other, mutually.<ref name="Allgaier2015">{{cite journal |last1=Allgaier |first1=C. |title=How can two soft bodied animals be precisely connected? A miniature quick-connect system in the slugs, ''Arion lusitanicus'' and ''Arion rufus''|journal=Journal of Morphology |date=2015 |volume=276 |issue=6 |pages=631–648 |doi=10.1002/jmor.20361|pmid=25532726 |bibcode=2015JMorp.276..631A |s2cid=29079897 }}</ref> This may take several attempts and sometimes is unsuccessful. Then the genital atria evert, and swell rapidly (1–2 min) to form a large, white, spherical mass between the bodies. The slugs remain like this for 90 minutes or longer, during which time a spermatophore is manufactured, filled with sperm, and in part passed over to the partner, hidden by the enveloping atria. Eventually one partner starts to become active, the configuration consequently rotates, the atria contract, and the genitalia separate. The spermatophores, anchored in the recipient's bursa trunk, are thereby pulled out of the donor's epiphallus. As the genitalia fully retract the spermatophore is taken in.<ref name="Dreijers2013">{{cite journal |last1=Dreijers |first1=E. |last2=Reise |first2=H. |last3=Hutchinson |first3=J.M.C. |title=Mating of the slugs ''Arion lusitanicus'' auct. non Mabille and ''A. rufus'' (L.): different genitalia and mating behaviours are incomplete barriers to interspecific sperm exchange |journal=Journal of Molluscan Studies |date=2013 |volume=79 |pages=51–63 |doi=10.1093/mollus/eys033|doi-access=free }}</ref>
==Gallery== <gallery class="center"> Arion rufus 1650.JPG|Dark individual Red slug (Arion rufus).JPG|Light individual Rode wegslak (Arion rufus), 07-09-2024. (actm.).jpg|Copulation Red Slug copulation.jpg|Mating </gallery>
==References== {{Reflist}}
==External links== * {{cite journal |last1=Reise, H., Schwarzer, A.-K., Hutchinson, J. M. C. & Schlitt, B. |title=Genital morphology differentiates three subspecies of the terrestrial slug Arion ater (Linnæus, 1758) s.l. and reveals a continuum of intermediates with the invasive A. vulgaris Moquin-Tandon, 1855 |journal=Folia Malacologica |date=2020 |volume=28 |issue=1 |pages=1-34 |url=https://www.foliamalacologica.com/Genital-morphology-differentiates-three-subspecies-of-the-terrestrial-slug-Arion,119132,0,2.html |access-date=1 November 2025}} * [http://eol.org/pages/403118/media ''Arion rufus''] at Encyclopedia of Life (3 pages) * [http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/species?id=1812 ''Arion rufus''] at Animalbase taxonomy, short description, distribution, biology, status (threats), images
{{Commons category|Arion rufus}} {{Taxonbar|from=Q2153396}} {{Authority control}}
ater rufus Category:Gastropods described in 1758 Category:Gastropods of Europe Category:Animal taxa named by Carl Linnaeus