"Pill bugs" of the family
Armadillidiidae are often confused with
pill millipedes such as Glomeris marginata, which is also widespread and common in Britain and Ireland, but pill millipedes have two pairs of legs per body segment, while woodlice have only seven pairs of legs.[5] Six certainly native species occur in the British Isles; some doubt exists as to the status of Eluma caelatum.
Armadillidium album is a pale-coloured species, and does not roll itself into a ball when disturbed. Rather, it remains stationary, but with its body slightly arched. It is only found at coastal sites, chiefly in
sand dunes, having been first discovered in Britain at the
Taw and
Torridge estuaries in
Devon in 1906.[3] It is found from the
Netherlands along the Atlantic coast of Europe to the Mediterranean, where it reaches as far east as
Greece.[2]
Armadillidium depressum is a large pill bug, up to 20 mm (0.79 in) long. Females are somewhat variable in colour, but males are uniformly
slate grey. It cannot roll up into a perfect ball, but leaves its
antennae and
telson exposed.[3] In the British Isles, it is only found in
South West England and
South Wales, but is also found in
Belgium,
France and
Italy.[2]
Like the previous species, Armadillidium nasatum cannot roll up into a perfect ball; it too leaves its
antennae and
telson exposed.[3] As well as being introduced to North America, it is found natively from Italy and northern Spain to the Netherlands and Britain,[2] where it is widely distributed across the southern half of the country.[3]
Armadillidium pictum occurs over most of Europe, where it is chiefly a forest species. In the British Isles, it is only known from a few sites, all remote from human habitation, in
Cumbria and
Powys. It closely resembles A. pulchellum, but it is darker in colour, with less distinct mottling, which is arranged in lines along the length of the body. It is also, at up to 9 mm (0.35 in) long, slightly larger than A. pulchellum.[3]
Armadillidium pulchellum may reach 6 mm (0.24 in) in length, and is covered with mosaic patterns of black, white, orange and red. The British Isles hold the greatest concentration of sites for this species,[3] which also extends across
Northern and
Western Europe.[2] In Great Britain, it is found on coastal cliffs and in upland areas, being particularly associated with Thymus spp.; in Ireland, its ecological tendencies are different, often being found in calcareous glacial sites, particularly
eskers.[3]
Armadillidium vulgare is the most common and thus the most well known of the pill bugs. It grows up to 14 mm (0.55 in) long, and is a uniform grey colour.[6] Its abundance tails off to the north and west, and is not known to occur north of a line between the estuaries of the
River Clyde and the
River Tay in
Scotland, or north-west of a line between
Galway and
Lough Foyle in
Ireland. It is associated with
sand dunes in the more north-westerly parts of its range, but is often replaced on
Carboniferous limestone by the related species Armadillidium pulchellum. Beyond Britain, it is found throughout
Europe and parts of
Asia, and has been introduced to
North America,
Australia,
South Africa and some islands in the
Atlantic and
Pacific Oceans.[3]
Eluma caelatum (previously Eluma purpurascens)[2] is typically 10 mm (0.39 in), but exceptionally up to 15 mm (0.59 in) long. The body is purplish brown, with a pair of single large, black
ocelli and a triangular
telson. It is abundant on cliffs on Ireland's east coast, although it is also found beside railway lines away from the sea, suggesting it was introduced with
railway ballast. In 1975, the species was discovered for the first time in Great Britain, and was originally known from two sites:
Overstrand,
Norfolk and near
Herne Bay,
Kent, both sites being coastal cliffs of soft rock.[3] It is now known to occur at numerous locations in south-east England (mainly Kent and Essex) including several non-coastal, man-made habitats.[7] It is found outside the British Isles on Atlantic coasts south to north-western Africa, as well as the
Canary Islands,
Azores and
Madeira. It has been introduced to
Tasmania and to
French Guiana, from where the
type specimen hails.[2]
Cylisticus convexus, the "curly woodlouse", has a scattered distribution across the British Isles. It seems to occur either in coastal sites, or
synanthropically in
anthropogenic habitats. It has been introduced to sites across the New World, from
Canada to
Argentina.[3]
Ligia oceanica, the sea slater, is the largest of the British woodlice, reaching a length of up to 30 mm (1.2 in). It is found on
rocky shores throughout the British Isles. Its wider range extends from
Norway to
Morocco, and has since been introduced to
North America.[3]
Oniscus asellus, the "common shiny woodlouse", is the most widespread species of woodlouse in the British Isles, both geographically and ecologically.[3] It is not known from the
Mediterranean Basin, but is widespread in
Northern and
Western Europe, as far east as the
Ukraine, as well as in the
Azores and
Madeira; it has also been widely introduced in
the Americas.[2] It is one of the largest native woodlice in Britain, at up to 16 mm (0.63 in) long.[9] It is relatively flat, and is a shiny patchy grey in colour.[3]
Originally described under the name Chaetophiloscia meeusei from greenhouses at the
Royal Botanic Gardens, Kew,[3]Burmoniscus meeusei is now known to occur in the wild in
Brazil,
Hawaii and
Taiwan.[2] It is not native to the British Isles.
Philoscia muscorum, the "common striped woodlouse" or "fast woodlouse", is up to 11 mm (0.43 in) long, with a greyish-brown, mottled, shiny body,[10] and long legs, which allow it to move quickly. It is more common in the south of the British Isles, but can be found up to the north coast of
Scotland.[3]
Although the generic placement of this species is uncertain, it is known to occur in the wild in
Mauritius and
Réunion, and is now established in greenhouses in England.[2] It is not native to the British Isles.
Acaeroplastes melanurus is known from much of southern Europe, from
Croatia to
Spain and the
Azores, and including
Algeria.[2] In the British Isles, it is only known from cliffs at
Howth,
County Dublin, where it was found several times between 1909 and 1934.[3] The species was rediscovered in 2002,[11] and further study showed that a substantial population still exists.[12]
Porcellio dilatatus is a widespread species, although only abundant at a few restricted sites. It is large and wide, with a rounded tip to the
telson in adults.[3]
Porcellio laevis is, when fully grown, the largest of the Porcellio species in the British Isles, at up to 18 mm (0.71 in) long.[6] It may be in decline due to the reduced availability of its preferred habitat; it was formerly common around horse dung.[3] It is more common in warmer climates, and is found across Europe and North Africa, as well as having been introduced to many other parts of the world.[2]
Porcellio scaber, the "common rough woodlouse", is one of the most frequent woodlice in the British Isles. It is also one of the best colonisers, having become established from
Iceland to
South America and
South Africa.[3] Adults may reach 11 mm (0.43 in) long.[6]
Porcellio spinicornis is confined to
stone walls and
buildings, with a tendency to avoid areas with a strong Atlantic climatic influence. It is distinctively marked, with two rows of yellow marks along the body against a brown background with a darker median stripe and a blackish head. Its wider distribution covers much of Europe, but little of the Mediterranean region, eastwards to
Ukraine; it has also been introduced to
Canada and the
United States.[3]
Porcellionides cingendus has an Atlantic, or
Lusitanian distribution, stretching from
Portugal to the British Isles,[2] and reaching its northernmost location at
St. John's Point, (near
Killough)
County Down. It partly replaces Philoscia muscorum where it occurs, and the two are easily confused in the field; Porcellionides cingendus, however, is narrower, and has a matt, not shiny, body.[3]
Porcellionides pruinosus is quite different from P. cingendus and the two are unlikely to be confused in the field. P. pruinosus has a characteristic dusty bloom and very pale legs. Although there is some doubt as to its native status in Britain, P. pruinosus has been found in Roman remains in London, indicating that if it was introduced, it was not introduced recently.[3] The species is predominantly Mediterranean in its distribution, but has taken on a
cosmopolitan distribution through the actions of man.[2]
Platyarthrus hoffmannseggi is closely associated with
ants' nests, particularly those of Lasius flavus, Lasius niger and species of Myrmica. It has a distinctive oval shape and short antennae. Its distribution appears to follow those of the ants with which it lives, and the British Isles are the north-westerly limit of its range. Elsewhere, P. hoffmannseggi extends south to the Mediterranean.[3] It is found outside Europe in
North Africa and
Turkey, and has been introduced to
North America.[2]
Trichorhina tomentosa is the only species of woodlouse originating in the
Americas to have become established in the British Isles, where it survives in greenhouses.[2]
Nagurus cristatus has a
pantropical distribution, and is found in greenhouses in
temperate climates, including in the British Isles,[2] though it is not a native species.
Trachelipus rathkei is sometimes confused with the more frequent Porcellio scaber, although its markings, with a regular longitudinal pattern of a light colour on a grey-brown background, are distinctive. They can be distinguished by examining the number of pleopodal lungs on the animal's underside with a
hand lens – species of Porcellio have only two pairs, while T. rathkei has five pairs.
Androniscus dentiger is readily recognisable by its distinctive pink colour, with a widening yellow stripe towards the rear. Adults are up to 6 mm (0.24 in) long. It is found at cliff sites, in scree and in caves, as well as in anthropogenic habitats. It is found as far south as
North Africa and east to
Croatia, and has been introduced to
North America.[3]
Buddelundiella cataractae is an inconspicuous woodlouse, up to 4 mm (0.16 in) long and similar in appearance to a grain of
sand when rolled up. Within Britain, it is only known from
Cardiff,
Barry and a site near
Snettisham,
Norfolk, although it has a wide distribution in Europe, possibly reaching as far east as
Georgia.[3]
Haplophthalmus danicus is reasonably widely distributed in the British Isles, but is rare outside
South East England. It is a pale animal, up to 4 mm (0.16 in) long, with longitudinal ridges along its body. It is found throughout Europe, in
Turkey,
North America,
Japan and several islands in the
Atlantic Ocean.[3]
Haplophthalmus mengei has a narrower body than H. danicus, but is a similar size and colour. It is found mostly in coastal or
limestone-rich sites. Outside Britain, the species is thought to occur as far east as
Austria and
Poland.[3]
Metatrichoniscoides celticus is the smallest of the British woodlice, at only 3 mm (0.12 in) long. It is white in appearance and is only known to occur along a 48 km (30 mi) stretch of the
Glamorgan coast.[3] It was discovered perhaps as late as 1979, and is listed as
vulnerable in the
IUCN Red List because of its small population size.[13] It is endemic to the British Isles.
Oritoniscus flavus is, despite the implication in its name, a dark
purple or
maroon colour, and can thus be told apart from the paler Trichoniscus pusillus. It is also, at 8 mm (0.31 in) long, slightly larger. It has a wide head and a tapering body, producing a shape reminiscent of a
trilobite. It is rare in
Great Britain, being found only in south
Wales and in Midlothian in
Scotland, but is widespread in
Ireland, and is found further afield in the
Pyrenees, leading to speculation that the species may be part of the "
Lusitanian fauna".[3]
As with the previous species, Trichoniscoides albidus has a misleading
specific epithet, since in life it is reddish-purple. It is similar to Trichoniscus pusillus, but its exoskeleton is dull, unlike the shiny surface in Trichoniscus pusillus. It is found in areas with an
Atlantic climate from
France to southern
Sweden.[3]
Trichoniscoides saeroeensis is distinctively coloured, with a pink
pleon, but a white
pereon, and with red or pink
ocelli. It is widely distributed around British and Irish coasts, and is also known from
Brittany,
Denmark and
Sweden.[3]
Trichoniscoides sarsi resembles the previous species, but has noticeable orange or pink patches on either side of its rear; unlike T. saeroeensis, however, T. sarsi is found inland.[3] It seems to tolerate cold especially well, and has been recorded outside the British Isles from France, Germany, Denmark, Sweden and
Norway, and has also been introduced to
Newfoundland.[2]
Trichoniscus pusillus, the "common pygmy woodlouse", is widespread in Europe north of the
Alps, and has been introduced to
Madeira, the
Azores and
North America.[2] In the south of its range, T. pusillusreproduces sexually, but towards the north of its range,
parthenogenesis predominates.[14] It is the most abundant woodlouse species in Britain,[15] and extremely widespread, occurring as far north as the northernmost tip of
Shetland.[3] It is shiny in appearance and reddish-brown in colour, with white patches visible on close inspection, where
muscles attach to the exoskeleton.[3] It reaches a maximum size of 5 mm (0.20 in) long.[16]
Trichoniscus pygmaeus is perhaps the most under-recorded British woodlouse species, since it lives deeply buried in the soil, and adults resemble immature individuals of the very abundant Trichoniscus pusillus.[3] It is found from
Morocco, across Europe, to south-western
Russia (
Krasnodar Krai).[2]
^N. Dias, M. Sprung & M. Hassall (2005). "The abundance and life histories of terrestrial isopods in a salt marsh of the Ria Formosa lagoon system, southern Portugal". Marine Biology. 147 (6): 1343–1352.
doi:
10.1007/s00227-005-0033-2.
S2CID84853859.
^Maria Wickenberg & Julian D. Reynolds (2002). "A recent Irish record of the woodlouse Acaeroplastes melanurus (Budde-Lund, 1885) (Isopoda: Porcellionidae), considered to be extinct in the British Isles". Bulletin of the Irish Biogeographical Society. 26: 60–63.
^Roy Anderson (2007). "Observations on the status and ecology of Acaeroplastes melanurus (Budde-Lund) (Crustacea: Oniscidea) at Howth Head, Dublin". Irish Naturalists' Journal. 28 (12): 497–505.
JSTOR25536869.
"Pill bugs" of the family
Armadillidiidae are often confused with
pill millipedes such as Glomeris marginata, which is also widespread and common in Britain and Ireland, but pill millipedes have two pairs of legs per body segment, while woodlice have only seven pairs of legs.[5] Six certainly native species occur in the British Isles; some doubt exists as to the status of Eluma caelatum.
Armadillidium album is a pale-coloured species, and does not roll itself into a ball when disturbed. Rather, it remains stationary, but with its body slightly arched. It is only found at coastal sites, chiefly in
sand dunes, having been first discovered in Britain at the
Taw and
Torridge estuaries in
Devon in 1906.[3] It is found from the
Netherlands along the Atlantic coast of Europe to the Mediterranean, where it reaches as far east as
Greece.[2]
Armadillidium depressum is a large pill bug, up to 20 mm (0.79 in) long. Females are somewhat variable in colour, but males are uniformly
slate grey. It cannot roll up into a perfect ball, but leaves its
antennae and
telson exposed.[3] In the British Isles, it is only found in
South West England and
South Wales, but is also found in
Belgium,
France and
Italy.[2]
Like the previous species, Armadillidium nasatum cannot roll up into a perfect ball; it too leaves its
antennae and
telson exposed.[3] As well as being introduced to North America, it is found natively from Italy and northern Spain to the Netherlands and Britain,[2] where it is widely distributed across the southern half of the country.[3]
Armadillidium pictum occurs over most of Europe, where it is chiefly a forest species. In the British Isles, it is only known from a few sites, all remote from human habitation, in
Cumbria and
Powys. It closely resembles A. pulchellum, but it is darker in colour, with less distinct mottling, which is arranged in lines along the length of the body. It is also, at up to 9 mm (0.35 in) long, slightly larger than A. pulchellum.[3]
Armadillidium pulchellum may reach 6 mm (0.24 in) in length, and is covered with mosaic patterns of black, white, orange and red. The British Isles hold the greatest concentration of sites for this species,[3] which also extends across
Northern and
Western Europe.[2] In Great Britain, it is found on coastal cliffs and in upland areas, being particularly associated with Thymus spp.; in Ireland, its ecological tendencies are different, often being found in calcareous glacial sites, particularly
eskers.[3]
Armadillidium vulgare is the most common and thus the most well known of the pill bugs. It grows up to 14 mm (0.55 in) long, and is a uniform grey colour.[6] Its abundance tails off to the north and west, and is not known to occur north of a line between the estuaries of the
River Clyde and the
River Tay in
Scotland, or north-west of a line between
Galway and
Lough Foyle in
Ireland. It is associated with
sand dunes in the more north-westerly parts of its range, but is often replaced on
Carboniferous limestone by the related species Armadillidium pulchellum. Beyond Britain, it is found throughout
Europe and parts of
Asia, and has been introduced to
North America,
Australia,
South Africa and some islands in the
Atlantic and
Pacific Oceans.[3]
Eluma caelatum (previously Eluma purpurascens)[2] is typically 10 mm (0.39 in), but exceptionally up to 15 mm (0.59 in) long. The body is purplish brown, with a pair of single large, black
ocelli and a triangular
telson. It is abundant on cliffs on Ireland's east coast, although it is also found beside railway lines away from the sea, suggesting it was introduced with
railway ballast. In 1975, the species was discovered for the first time in Great Britain, and was originally known from two sites:
Overstrand,
Norfolk and near
Herne Bay,
Kent, both sites being coastal cliffs of soft rock.[3] It is now known to occur at numerous locations in south-east England (mainly Kent and Essex) including several non-coastal, man-made habitats.[7] It is found outside the British Isles on Atlantic coasts south to north-western Africa, as well as the
Canary Islands,
Azores and
Madeira. It has been introduced to
Tasmania and to
French Guiana, from where the
type specimen hails.[2]
Cylisticus convexus, the "curly woodlouse", has a scattered distribution across the British Isles. It seems to occur either in coastal sites, or
synanthropically in
anthropogenic habitats. It has been introduced to sites across the New World, from
Canada to
Argentina.[3]
Ligia oceanica, the sea slater, is the largest of the British woodlice, reaching a length of up to 30 mm (1.2 in). It is found on
rocky shores throughout the British Isles. Its wider range extends from
Norway to
Morocco, and has since been introduced to
North America.[3]
Oniscus asellus, the "common shiny woodlouse", is the most widespread species of woodlouse in the British Isles, both geographically and ecologically.[3] It is not known from the
Mediterranean Basin, but is widespread in
Northern and
Western Europe, as far east as the
Ukraine, as well as in the
Azores and
Madeira; it has also been widely introduced in
the Americas.[2] It is one of the largest native woodlice in Britain, at up to 16 mm (0.63 in) long.[9] It is relatively flat, and is a shiny patchy grey in colour.[3]
Originally described under the name Chaetophiloscia meeusei from greenhouses at the
Royal Botanic Gardens, Kew,[3]Burmoniscus meeusei is now known to occur in the wild in
Brazil,
Hawaii and
Taiwan.[2] It is not native to the British Isles.
Philoscia muscorum, the "common striped woodlouse" or "fast woodlouse", is up to 11 mm (0.43 in) long, with a greyish-brown, mottled, shiny body,[10] and long legs, which allow it to move quickly. It is more common in the south of the British Isles, but can be found up to the north coast of
Scotland.[3]
Although the generic placement of this species is uncertain, it is known to occur in the wild in
Mauritius and
Réunion, and is now established in greenhouses in England.[2] It is not native to the British Isles.
Acaeroplastes melanurus is known from much of southern Europe, from
Croatia to
Spain and the
Azores, and including
Algeria.[2] In the British Isles, it is only known from cliffs at
Howth,
County Dublin, where it was found several times between 1909 and 1934.[3] The species was rediscovered in 2002,[11] and further study showed that a substantial population still exists.[12]
Porcellio dilatatus is a widespread species, although only abundant at a few restricted sites. It is large and wide, with a rounded tip to the
telson in adults.[3]
Porcellio laevis is, when fully grown, the largest of the Porcellio species in the British Isles, at up to 18 mm (0.71 in) long.[6] It may be in decline due to the reduced availability of its preferred habitat; it was formerly common around horse dung.[3] It is more common in warmer climates, and is found across Europe and North Africa, as well as having been introduced to many other parts of the world.[2]
Porcellio scaber, the "common rough woodlouse", is one of the most frequent woodlice in the British Isles. It is also one of the best colonisers, having become established from
Iceland to
South America and
South Africa.[3] Adults may reach 11 mm (0.43 in) long.[6]
Porcellio spinicornis is confined to
stone walls and
buildings, with a tendency to avoid areas with a strong Atlantic climatic influence. It is distinctively marked, with two rows of yellow marks along the body against a brown background with a darker median stripe and a blackish head. Its wider distribution covers much of Europe, but little of the Mediterranean region, eastwards to
Ukraine; it has also been introduced to
Canada and the
United States.[3]
Porcellionides cingendus has an Atlantic, or
Lusitanian distribution, stretching from
Portugal to the British Isles,[2] and reaching its northernmost location at
St. John's Point, (near
Killough)
County Down. It partly replaces Philoscia muscorum where it occurs, and the two are easily confused in the field; Porcellionides cingendus, however, is narrower, and has a matt, not shiny, body.[3]
Porcellionides pruinosus is quite different from P. cingendus and the two are unlikely to be confused in the field. P. pruinosus has a characteristic dusty bloom and very pale legs. Although there is some doubt as to its native status in Britain, P. pruinosus has been found in Roman remains in London, indicating that if it was introduced, it was not introduced recently.[3] The species is predominantly Mediterranean in its distribution, but has taken on a
cosmopolitan distribution through the actions of man.[2]
Platyarthrus hoffmannseggi is closely associated with
ants' nests, particularly those of Lasius flavus, Lasius niger and species of Myrmica. It has a distinctive oval shape and short antennae. Its distribution appears to follow those of the ants with which it lives, and the British Isles are the north-westerly limit of its range. Elsewhere, P. hoffmannseggi extends south to the Mediterranean.[3] It is found outside Europe in
North Africa and
Turkey, and has been introduced to
North America.[2]
Trichorhina tomentosa is the only species of woodlouse originating in the
Americas to have become established in the British Isles, where it survives in greenhouses.[2]
Nagurus cristatus has a
pantropical distribution, and is found in greenhouses in
temperate climates, including in the British Isles,[2] though it is not a native species.
Trachelipus rathkei is sometimes confused with the more frequent Porcellio scaber, although its markings, with a regular longitudinal pattern of a light colour on a grey-brown background, are distinctive. They can be distinguished by examining the number of pleopodal lungs on the animal's underside with a
hand lens – species of Porcellio have only two pairs, while T. rathkei has five pairs.
Androniscus dentiger is readily recognisable by its distinctive pink colour, with a widening yellow stripe towards the rear. Adults are up to 6 mm (0.24 in) long. It is found at cliff sites, in scree and in caves, as well as in anthropogenic habitats. It is found as far south as
North Africa and east to
Croatia, and has been introduced to
North America.[3]
Buddelundiella cataractae is an inconspicuous woodlouse, up to 4 mm (0.16 in) long and similar in appearance to a grain of
sand when rolled up. Within Britain, it is only known from
Cardiff,
Barry and a site near
Snettisham,
Norfolk, although it has a wide distribution in Europe, possibly reaching as far east as
Georgia.[3]
Haplophthalmus danicus is reasonably widely distributed in the British Isles, but is rare outside
South East England. It is a pale animal, up to 4 mm (0.16 in) long, with longitudinal ridges along its body. It is found throughout Europe, in
Turkey,
North America,
Japan and several islands in the
Atlantic Ocean.[3]
Haplophthalmus mengei has a narrower body than H. danicus, but is a similar size and colour. It is found mostly in coastal or
limestone-rich sites. Outside Britain, the species is thought to occur as far east as
Austria and
Poland.[3]
Metatrichoniscoides celticus is the smallest of the British woodlice, at only 3 mm (0.12 in) long. It is white in appearance and is only known to occur along a 48 km (30 mi) stretch of the
Glamorgan coast.[3] It was discovered perhaps as late as 1979, and is listed as
vulnerable in the
IUCN Red List because of its small population size.[13] It is endemic to the British Isles.
Oritoniscus flavus is, despite the implication in its name, a dark
purple or
maroon colour, and can thus be told apart from the paler Trichoniscus pusillus. It is also, at 8 mm (0.31 in) long, slightly larger. It has a wide head and a tapering body, producing a shape reminiscent of a
trilobite. It is rare in
Great Britain, being found only in south
Wales and in Midlothian in
Scotland, but is widespread in
Ireland, and is found further afield in the
Pyrenees, leading to speculation that the species may be part of the "
Lusitanian fauna".[3]
As with the previous species, Trichoniscoides albidus has a misleading
specific epithet, since in life it is reddish-purple. It is similar to Trichoniscus pusillus, but its exoskeleton is dull, unlike the shiny surface in Trichoniscus pusillus. It is found in areas with an
Atlantic climate from
France to southern
Sweden.[3]
Trichoniscoides saeroeensis is distinctively coloured, with a pink
pleon, but a white
pereon, and with red or pink
ocelli. It is widely distributed around British and Irish coasts, and is also known from
Brittany,
Denmark and
Sweden.[3]
Trichoniscoides sarsi resembles the previous species, but has noticeable orange or pink patches on either side of its rear; unlike T. saeroeensis, however, T. sarsi is found inland.[3] It seems to tolerate cold especially well, and has been recorded outside the British Isles from France, Germany, Denmark, Sweden and
Norway, and has also been introduced to
Newfoundland.[2]
Trichoniscus pusillus, the "common pygmy woodlouse", is widespread in Europe north of the
Alps, and has been introduced to
Madeira, the
Azores and
North America.[2] In the south of its range, T. pusillusreproduces sexually, but towards the north of its range,
parthenogenesis predominates.[14] It is the most abundant woodlouse species in Britain,[15] and extremely widespread, occurring as far north as the northernmost tip of
Shetland.[3] It is shiny in appearance and reddish-brown in colour, with white patches visible on close inspection, where
muscles attach to the exoskeleton.[3] It reaches a maximum size of 5 mm (0.20 in) long.[16]
Trichoniscus pygmaeus is perhaps the most under-recorded British woodlouse species, since it lives deeply buried in the soil, and adults resemble immature individuals of the very abundant Trichoniscus pusillus.[3] It is found from
Morocco, across Europe, to south-western
Russia (
Krasnodar Krai).[2]
^N. Dias, M. Sprung & M. Hassall (2005). "The abundance and life histories of terrestrial isopods in a salt marsh of the Ria Formosa lagoon system, southern Portugal". Marine Biology. 147 (6): 1343–1352.
doi:
10.1007/s00227-005-0033-2.
S2CID84853859.
^Maria Wickenberg & Julian D. Reynolds (2002). "A recent Irish record of the woodlouse Acaeroplastes melanurus (Budde-Lund, 1885) (Isopoda: Porcellionidae), considered to be extinct in the British Isles". Bulletin of the Irish Biogeographical Society. 26: 60–63.
^Roy Anderson (2007). "Observations on the status and ecology of Acaeroplastes melanurus (Budde-Lund) (Crustacea: Oniscidea) at Howth Head, Dublin". Irish Naturalists' Journal. 28 (12): 497–505.
JSTOR25536869.