Arion intermedius

It is native to Western Europe and a part of Central Europe, from northern Portugal to western Poland, and from southern Scandinavia to northern Italy. It is believed native to Czechia, where the majority of its records come from various types of forests.{{Cite journal|last=Čejka|first=Tomáš|last2=Beran|first2=Luboš|last3=Coufal|first3=Radovan|last4=Dvořák|first4=Libor|last5=Hlaváč|first5=Jaroslav Č|last6=Horáčková|first6=Jitka|last7=Horsáková|first7=Veronika|last8=Juřičková|first8=Lucie|last9=Kosová|first9=Tereza|last10=Čačaný|first10=Juraj|last11=Szabóová|first11=Dana|date=2021-09-16|title=Malacological news from the Czech and Slovak Republics in 2020|url=https://zenodo.org/records/7018688/files/20.Cejka.pdf|journal=Malacologica Bohemoslovaca|language=English|volume=20|pages=56–74|doi=10.5817/MaB2021-20-56|issn=1336-6939|doi-access=free}} Records at the edge of its European range more likely to be the result of introductions are from Slovakia, Austria, Hungary, Bulgaria, Finland, Iceland, and southern Italy. It has also been introduced to many regions beyond Europe, including North and South America, Australia, New Zealand, South Africa, and some Pacific islands.{{cite book |last1=Herbert |first1=D. |title=The introduced terrestrial Mollusca of South Africa |date=2010 |publisher=SANBI| location=Pretoria|url=https://www.sanbi.org/sites/default/files/documents/documents/bioseries15introterrestmollusca.pdf}}{{cite journal |last1=Araiza-Gómez |first1=V. |last2=Naranjo-García |first2=E. |last3=Zúñiga |first3=G. |title=Occurrence in Mexico of two European invasive slug species: Arion vulgaris Moquin-Tandon, 1855 and Arion intermedius (Norman, 1852) |journal=BioInvasions Records |date=2021 |volume=10 |issue=1 |pages=10–20 |doi=10.3391/bir.2021.10.1.02|doi-access=free }}

This slug is 1.5 to 2 cm long when adult. It is variable in color and patterning, being white, pale yellowish or gray, with or without lateral bands, and it has darker gray tentacles and a yellow or orange sole. It becomes compact and "nearly bell-shaped" when contracted. The tubercles that texture the dorsal surface of its body taper to sharp, prickle-like points, inspiring the common name hedgehog slug. This appearance of the tubercles is diagnostic of the species, although the prickliness usually disappears when the slug is preserved. Another useful character is a line of very small black dots along the margin of the sole at the anterior end, although they are not always apparent.{{cite journal |last1=Turóci |first1=Á. |last2=Hutchinson |first2=J.M.C. |last3=Schlitt |first3=B. |last4=Vidéki |first4=R. |last5=Farkas |first5=R. |last6=Németh |first6=M.Z. |last7=Borostyán |first7=K. |last8=Páll-Gergely |first8=B. |title=First records of Arion intermedius and Arion transsylvanus (Stylommatophora: Arionidae) in Hungary |journal=Ecologica Montenegrina |date=21 March 2025 |volume=83 |pages=12–28 |doi=10.37828/em.2025.83.2|doi-access=free }}

This species occurs in natural habitat such as grasslands and forests, and on cultivated or otherwise human-altered land, such as pastures, orchards, and hedges. It feeds on plants and fungi.[http://anrcatalog.ucdavis.edu/pdf/8336.pdf Slugs: A Guide to the Invasive and Native Fauna of California.] Division of Agriculture and Natural Resources. University of California. 2009.

For a long time, this hermaphroditic slug was thought to reproduce only by self-fertilization; solitary captive specimens produced offspring and the species had never been observed mating. Genetic analysis provided evidence of crossing and the species is now believed to have a mixed breeding system, with an individual having the ability to fertilize itself or cross-fertilize, exchanging sperm with a mate.{{cite journal|last1=Jordaens|first1=K.|last2=Van Houte|first2=N.|last3=Helsen|first3=P.|last4=Breugelmans|first4=K.|last5=Jaksons|first5=P.|last6=Backeljau|first6=t.|date=2013 |title=Mixed breeding system in the hermaphroditic land slug Arion intermedius (Stylommatophora, Arionidae)|doi=10.1111/j.1601-5223.2013.02272.x|journal=Hereditas|volume=150|issue=4–6|pages=45–52|pmid=24164457|doi-access=free|hdl=10067/1157380151162165141|hdl-access=free}}

In the wild it has one generation per year (univoltine), with all individuals maturing rather synchronously in autumn.{{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|pages=88–105|doi=10.1093/mollus/eyw042|url=http://www.senckenberg.de/files/content/forschung/abteilung/zoologie/malakologie/malak/hutch/hutchpub/jms5.htm|doi-access=free}} Adults die over winter or early spring.{{cite journal|last1=Bohan|first1=D.A.|last2=Glen|first2=D.M.|last3=Wiltshire|first3=C.W.|last4=Hughes|first4=L.|date=2000|title=Parametric intensity and the spatial arrangement of the terrestrial mollusc herbivores Deroceras reticulatum and Arion intermedius |doi=10.1111/j.1365-2656.2000.00459.x|journal=Journal of Animal Ecology |volume= 69|issue=6|pages= 1031–1046|doi-access=free}}

This is not considered to be a severe pest, but some reports of such problems have been made. While most exotic slugs and snails are often found in altered environments, this species has a greater tendency to invade natural habitat, such as forests. Its ability to self-fertilize allows a single individual to enter new habitat and then reproduce.{{cite journal |last1=Cádiz |first1=Francisco J |last2=Gallardo |first2=Carlos S |title=Arion intermedius (Gastropoda: Stylommatophora): first record of this introduced slug in Chile, with notes on its anatomy and natural history |journal=Revista Chilena de Historia Natural |date=2007 |volume=80 |issue=1 |pages=99-108 |doi=10.4067/S0716-078X2007000100008}} It is also known as a pest of clover-seeded pastures in New Zealand.Barker, G. M. (1989). [http://www.cabdirect.org/abstracts/19891135793.html Slug problems in New Zealand pastoral agriculture.] Monograph-British Crop Protection Council (41), 59–68.

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• [http://www.animalbase.uni-goettingen.de/zooweb/servlet/AnimalBase/home/species?id=2531 Arion intermedius] at Animalbase taxonomy,short description, distribution, biology,status (threats), images
• [http://eol.org/pages/455166/media Arion intermedius] images at Encyclopedia of Life

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Category:Arion (gastropod)

Category:Gastropods described in 1852

Category:Molluscs of Europe