Oniscus asellus
{{Short description|Species of woodlouse}}
{{Speciesbox
| image = Common Shiny Woodlouse (30538333473).jpg
| genus = Oniscus
| species = asellus
| synonyms = {{Collapsible list|bullets=bulletson
|Oniscus affinis
|Oniscus fossor
|Oniscus lamperti
|Oniscus languidus
|Oniscus lineatus
|Oniscus murarius
|Oniscus nodulosus
|Oniscus taeniola
|Oniscus vicarius
|Porcellio Dio lineatus
|Porcellio Cane taeniola
}}
}}
Oniscus asellus, the common woodlouse, or common shiny woodlouse is one of the largest and most common species of woodlouse native to the British Isles and Western and Northern Europe, growing to lengths of 16 mm and widths of 6 mm. Oniscus asellus was first described by Swedish biologist Carl Linnaeus in his Systema Naturae, and is a very common species, representing in Britain "the archetypal 'woodlouse' familiar to the general public". It lives in a great variety of habitats, but favours damp conditions, especially under rotting wood. O.asellus is also a successfully synanthropic species, dwelling in gardens, walls, and inside houses.
Classification
Oniscus asellus was described as Oniscus Aſellus in the tenth edition of Systema Naturae by Carl Linnaeus, in 1758.{{Cite book |last=Linné |first=Carl von |url=https://www.biodiversitylibrary.org/item/10277#page/659/mode/1up |title=Systema naturae per regna tria naturae s ecundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis |date= |publisher=Impensis Direct. Laurentii Salvii |year=1758 |edition=10th |volume=v.1 |location=Holmiae |page=637}}
The subspecies common in most of the world is O. asellus asellus, but in western France{{Cite web |title=Oniscus asellus occidentalis Bilton, 1994 |url=https://www.gbif.org/species/9637758 |access-date=2025-03-15 |website=www.gbif.org |language=en}} and southeastern Britain, a genetically distinct form of the common woodlouse has been identified and classified as a subspecies. O. asellus occidentalis was described in 1994, tends to be smaller but more colourful, and has a slightly different body shape. The two subspecies are able to interbreed and produce hybrids which mix their physical characteristics.{{Cite web |title=Oniscus asellus ssp. occidentalis {{!}} British Myriapod and Isopod Group |url=https://bmig.org.uk/species/oniscus-asellus-ssp-occidentalis |access-date=2025-03-15 |website=bmig.org.uk}}
Distribution
The common woodlouse is the most widespread species of woodlouse in the British Isles, both geographically and ecologically, being one of the "most pervasive" of Britain's wildlife. It is adapted equally well to northern areas as to southern ones, and has been recorded in every vice-county of England, Scotland, Wales, and Ireland.{{cite book |author=Paul T. Harding & Stephen L. Sutton |url=http://nora.nerc.ac.uk/5276/1/Woodlice.pdf |title=Woodlice in Britain and Ireland: distribution and habitat |publisher=Abbots Ripton, Huntingdon, Institute of Terrestrial Ecology |year=1985 |isbn=0-904282-85-6 |pages=68–9}} It is rare in the Mediterranean Basin, but is widespread in Northern and Western Europe, as far east as Ukraine, as well as in the Azores and Madeira; it has also been widely introduced in the Americas, predominantly in Mexico and in the United States, east of the Mississippi River and west of the Rocky Mountains. According to the British Myriapod and Isopod Group, Oniscus asellus, along with Porcellio scaber, "represents the archetypal 'woodlouse' familiar to the general public". As of April 2025, Oniscus asellus is the third-most observed species of woodlouse in the world in the citizen science website iNaturalist, after Porcellio scaber and Armadillidium vulgare.{{Cite web |title=Observations |url=https://www.inaturalist.org/observations?subview=map&taxon_id=84718&view=species |url-status=live |access-date=2025-04-20 |website=iNaturalist |language=en}}
File:Common Shiny Woodlouse, Berlin, Berlin, Germany imported from iNaturalist photo 254310891.jpg
Description
= General appearance =
The common woodlouse is one of the largest native woodlice in Britain, at up to {{convert|16|mm|mil|2|lk=on}} long.{{cite web |url=http://www.arkive.org/common-woodlouse/oniscus-asellus/info.html |title=Common woodlouse (Oniscus asellus) |publisher=ARKive.org |access-date=February 22, 2009 |archive-url=https://web.archive.org/web/20100429175351/http://www.arkive.org/common-woodlouse/oniscus-asellus/info.html |archive-date=2010-04-29 |url-status=dead }} It is relatively flat, and is a shiny brown-grey in colour, but paler-coloured specimens sometimes occur.{{Cite web |title=Oniscus asellus ssp. asellus {{!}} British Myriapod and Isopod Group |url=https://bmig.org.uk/species/oniscus-asellus-ssp-asellus |access-date=2025-03-14 |website=bmig.org.uk}} The juveniles have rough bumps and orange markings, leading them to sometimes be misidentified as Porcellio scaber. In his 1758 description, Linnaeus gave the defining characteristics of O. asellus as an oval shape, broad abdomen, and bifurcated tail.
= External morphology =
All members of the genus Oniscus are defined by several morphological characteristics. Flagella in isopods are a set of small segments at the antenna tip;{{Cite web |title=Woodlice: types of antennal flagellum {{!}} British Myriapod and Isopod Group |url=https://bmig.org.uk/image/woodlice-types-antennal-flagellum |access-date=2025-03-28 |website=bmig.org.uk}} Oniscus species have three-segmented flagella, along with a wide abdomen and a head with lateral lobes. They are unable to completely roll themselves up into a ball.{{Cite book |last=Webb |first=Wilfred Mark |url=https://archive.org/details/britishwoodliceb00webb/page/n5/mode/2up?q=oniscus+asellus |title=The British woodlice |year=1906 |pages=27–8}} Harriet Richardson described the body of O. asellus as being about one and half times longer than it is wide, about {{Convert|10 by 16|mm|mil|lk=out|abbr=on}}. The head is longer than it is wide, measuring {{Convert|2 by 3|mm|mil|lk=out|abbr=on}}, with the front margin slightly convex. There are pronounced, narrow, elongate lobes, located anterolaterally, nearly {{Convert|1|mm|mil|abbr=on}} long and rounded anteriorly. The compound eyes are small and situated on the sides of the head at the base of the prominent lobes. There are two pairs of antennae; the first, inconspicuous and comprising only a couple segments; the second is composed of five segments, each longer than the first. The segments of the thorax are nearly equal in length. The first segment has projections which extend to surround the head, and all segments are expanded to the sides, with straight lateral margins. The segments of the abdomen are distinct, with the first two being somewhat shorter, and their lateral parts covered by the overhanging seventh segment of the thorax. The abdominal segments three to five have extensions which continue the oval outline of the body. The lateral extensions of the fifth segment extend far back, as far as the extremity of the sixth and ultimate segment. This final segment has a triangular shape, with the apex formed from a process pointed posteriorly. The uropoda are mostly covered by the final abdominal segment.{{Cite book |last=Searle |first=Harriet Richardson |author-link=Harriet Richardson |url=https://www.google.ca/books/edition/A_Monograph_on_the_Isopods_of_North_Amer/hQkyHCoHdIEC?hl=en&gbpv=1 |title=A Monograph on the Isopods of North America |date=1905 |publisher=U.S. Government Printing Office |pages=600–2 |language=en}} {{source-attribution|inline=yes}}
= Moulting =
Pale patches are often visible on the back of Oniscus asellus; these are areas that store calcium, which is then used to reinforce the exoskeleton after a moult. Moulting occurs in two halves, with the rear half moulting before the front half. The exuvia (the thing that is being moulted) is often consumed by the animal after moulting.
= Reproductive anatomy =
Female Oniscus asellus woodlice have two tube-shaped ovaries. These are located on either side of the woodlouse's gut and run much of the animal's body length. Female germ cells, or ovocytes, are found in the ovary in varying sizes.{{Cite journal |last=King |first=S. D. |year=1926 |title=Oogenesis in Oniscus Asellus |url=https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.1926.0029 |journal=Proceedings of the Royal Society |doi=10.1098/rspb.1926.0029}} In males, meanwhile, there are two testes, each comprising three "narrow lobes" with three corresponding into the vas deferens. Inside the lobes, germ cells develop; each lobe "may be divided into two principal regions of growth, composed of cells of different generations and of differing degrees of development."{{Cite journal |last=Nichols |first=M. Louise |year=1901 |title=The spermatogenesis of Oniscus asellus Linn., with especial reference to the history of the chromatin. |url=https://ia600805.us.archive.org/view_archive.php?archive=/13/items/crossref-pre-1909-scholarly-works/10.1086%252F276675.zip&file=10.1086%252F278028.pdf |journal=The American Naturalist |volume=35 |page=919}}
Ecology
The common woodlouse occurs in a wide range of habitats, including some with little available calcium, but not dry ones. The species is found both inland and in coastal areas, chiefly in the countryside, but the species is also a successful synanthrope, and is frequent inhabitant of human spaces such as greenhouses, gardens, and parks. The common woodlouse is found in waste grounds, open woodlands, forests, and gardens, as well as in grasslands, scrub, and around buildings. The plurality (22%) of records examined in one study were found on road verges, although it has also been collected from cliff faces and quarries. It most commonly dwells in moist environments under rocks or dead wood, but has also been recorded from litter, human constructions, and garbage. It is especially prevalent in rotting wood, a tendency which allows it to inhabit areas otherwise unfriendly to woodlice such as moorlands. Linnaeus in 1758 noted it was found in houses, but also rotting wood, hibernacula, and walls.
= Heavy metal accumulation =
Isopods are known to store high levels of lead, copper, zinc, and cadmium from contaminated environments in their hepatopancreas, an organ which is believed to be "the most important [...] to monitor the effects of heavy metal pollution" in some isopod species, including O. asellus.{{cite book |author1=Claus Svendsen |title=Environmental Analysis of Contaminated Sites |author2=Graeme Paton |author3=Jason M. Weeks |publisher=John Wiley and Sons |year=2002 |isbn=978-0-471-98669-0 |editor1=G. I. Sunahara |pages=95–134 |chapter=Soil biomarkers (invertebrates and microbes) for assessing site toxicity |editor2=A. Y. Renoux |editor3=C. Thellen |editor4=C. L. Gaudet |editor5=A. Pilon |chapter-url=https://books.google.com/books?id=lvCB5H6pkqYC&pg=PA110}} In fact, the concentrations of these four elements in the hepatpancreata of O. asellus living in contaminated environments "are among the highest so far recorded in the soft tissues of any animal". It is thought that retaining non-essential elements such as cadmium takes less energy than preparing to excrete them. It is also believed that woodlice that live in contaminated environments have larger hepatopancreata, allowing them to process more material, based on a positive correlation between the level of contamination of the leaf litter and the dry weight of the hepatopancreata of woodlice living there.{{Cite journal |last=Hopkin |first=S. P. |last2=Martin |first2=M. H. |date=1982 |title=The Distribution of Zinc, Cadmium, Lead and Copper within the Woodlouse Oniscus asellus (Crustacea, Isopoda) |url=https://www.jstor.org/stable/4216753 |journal=Oecologia |volume=54 |issue=2 |pages=227–232 |issn=0029-8549}} A 1990 study comparing the abilities of O. asellus and Porcellio scaber showed that O. asellus dumped zinc rapidly whereas P. scaber retained it, while O. asellus retained much more cadmium and lead – on average about five times as much. Copper was accumulated by both species.{{Cite journal |last=Hopkin |first=S. P. |date=1990 |title=Species-Specific Differences in the Net Assimilation of Zinc, Cadmium, Lead, Copper and Iron by the Terrestrial Isopods Oniscus asellus and Porcellio scaber |url=https://www.jstor.org/stable/2404294 |journal=Journal of Applied Ecology |volume=27 |issue=2 |pages=460–474 |doi=10.2307/2404294 |issn=0021-8901}}
= Conservation =
The subspecies O. asellus occidentalis faces multiple threats: its populations are fragmented, and it is also threatened by hybridisation with O. asellus asellus. In Britain, it is classified as "Near Threatened".{{Cite journal |last=Gregory |first=Steve J. |date=2024 |title=15 years on: An update to Woodlice and Waterlice in Britain and Ireland, part 1 ~ Native and Naturalised Species |url=https://bmig.org.uk/sites/default/files/bulletin/BullBMIG36-2024_complete.pdf#page=22 |journal=Bulletin of the British Myriapod & Isopod Group |publisher=British Myriapod and Isopod Group |volume=36 |page=51 |issn=2513-9444}}
See also
References
External links
- {{Commons category-inline}}
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