Isopods

Order Isopoda

The Isopods (Order Isopoda) includes 88 species across 22 families and 62 genera in our directory.

About Isopods

Isopoda includes ~10,000 described species of woodlice, pill bugs, and sea slaters. Woodlice are the only crustaceans to have fully adapted to life on land. Pill bugs (roly-polies) can roll into a perfect ball for defense.

Economic Impact

Woodlice are generally beneficial in gardens as decomposers, though they can occasionally damage seedlings and soft fruits in large numbers.

Ecological Role

Woodlice are critical soil decomposers, breaking down dead plant material and recycling calcium and other nutrients. They breathe through gill-like structures and require moist environments. Giant deep-sea isopods (Bathynomus) can grow up to 50cm long.

Families in Isopoda (22)

Species in Isopoda (88)

Armadilloniscus holmesi

Detonidae

Identification: pointed rostrum distinguishes it from A. lindahli

Brickwork Woodlouse

Porcellio spinicornis

Porcellionidae

Identification: "Broad, flattened species. The markings are characteristic: the head is dark brown and the back is marked with a dark central stripe, flanked by 2 rows of yellow spots on a pale background. The first two pairs of pleopods possess pleo

Carpias minutus

Janiridae

Identification: Figured male Males with greatly enlarged first chela

Cirolanides texensis

Cirolanidae

Type Locality: artesian well, San Marcos, Hays Co., Texas

Common Pillbug

Armadillidium vulgare

Armadillidiidae

Identification: Some identification marks mentioned by Ferenc Vilisics in his comment on this picture: Additional information is available at Discover Life . Introduced worldwide from Europe. It has been shown to modify the top soil layer (increased

Common Rough Woodlouse

Porcellio scaber

Porcellionidae

Identification: The rough surface and the the dark color distinguish it from Oniscus asellus , as does the apiculate middle lobe on the head. [from comment by Ferenc Vilisics] Densely covered with tubercles. Usually dark grey, sometimes quite red or

Conasellus racovitzai

Asellidae

Identification: The two subspecies (likely to be full species) are mostly told apart by range, although there are some morphological differences too. This should be helpful in the west, where it's unclear which subspecies is introduced (although ssp.

Curly Woodlouse

Cylisticus convexus

Cylisticidae

Identification: capable of rolling into a ball; dorsal surface dark, glossy, grayish-black, marked with pale translucent streaks; uropods extend beyond terminal abdominal segment; abdomen not abruptly narrower than thorax; flagellum of second antenna

European Sowbug

Oniscus asellus

Oniscidae

Identification: Flat, brown-black with pale mottling and pale edges to the segmental plates. The body ends in a two-pointed segment - the telson . - shiny, even surface, greyish colour with white margins, sometimes with little yellow dots. - wide ova

Florida Fast Woodlouse

Atlantoscia floridana

Philosciidae

Identification: The "robber mask" is diagnostic, although some individuals may have an entirely dark head Appears to be abundant in Florida

Idotea metallica

Idoteidae

Identification: Among New England valviferan isopods (and probably among other regional valviferan fauna as well), can be identified by the blunt, squared off shape of the telson. Also distinctive is the metallic blue coloration.

Idotea phosphorea

Idoteidae

Identification: Can be separated from other Idotea species by the shape of its telson.

Jaera albifrons

Janiridae

Identification: See: and A Monograph on the Isopods of North America Can only be told from other members of the complex by the combination of the first to fourth male walking legs being normal and the sixth and seventh male walking legs with large lo

Ligia pallasii

Ligiidae

Identification: The eyes are separated by a distance equal to twice the greatest diameter of an eye. They have short uropods, and a basal segment as long as broad.

Nosy Pillbug

Armadillidium nasatum

Armadillidiidae

Identification: Best told from A. vulgare by the conspicous "nose tab" and the rounded telson tip. The color pattern can also be used but there is some overlap that makes it very hard to confidentially tell them apart using color without experience

Philoscia muscorum

Philosciidae

Identification: Brownish mottled with pale patches and a clear dark stripe along the back

Plum Woodlouse

Porcellionides pruinosus

Porcellionidae

Identification: External diagnostic features (Ferenc Vilisics's comments ): More here

Porcellionides floria

Porcellionidae

Identification: P. floria was separated from the European P. pruinosus by Garthwaite and Sassaman (1985), but morphologically the two species are very similar. Both are widespread, synanthropic species in the USA; all the specimens examined from S. C

Saduria entomon

Chaetiliidae

Identification: Saduria sabini , which reaches as far south as Alaska and the Gulf of St. Lawrence, lacks eyes

Sphaeroma papillae

Sphaeromatidae

Identification: Only overlaps in range with Cassidinidea ovalis and Sphaeroma quadridentatum , see for specific features to tell them apart:

Sphaeroma quadridentatum

Sphaeromatidae

Identification: Differs from Sphaeroma papillae in several notable ways: telson is more rounded, outer margin of second uropod is serrated, coloration is much different, and abdominal segments are differently shaped in a number of places.

Swift Woodlouse

Porcellio laevis

Porcellionidae

Identification: The smoothly glossy, dark and essentially unpatterned dorsal surface of P. laevis , the sharply triangular telson and long uropods are distinctive among the introduced European Porcellio spp. -- J. Wright's comment source:

Western Seaslater

Ligia occidentalis

Ligiidae

Identification: distinguished from L. pallasi by the much longer uropods; eyes larger & closer together (1 eye diameter apart); body much sleeker; and the tendency to bolt when disturbed