Woodlouse

Woodlice
Oniscus asellus
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Isopoda
Suborder:	Oniscidea Latreille, 1802
Infraorders and Families
Infaroder/Section Diplocheta Familia: Ligiidae Infraorder Holoverticata Section: Tylida Familia: Tylidae Section: Microcheta Familia: Mesoniscidae Section: Synocheta Schoebliidae Styloniscidae Titaniidae Trichoniscidae Turanoniscidae Section: Crinocheta Bathytropidae Berytoniscidae Detonidae Halophilosciidae Olibrinidae Oniscidae Philosciidae Platyarthridae Pudeoniscidae Rhyscotidae Scyphacidae Speleoniscidae Sphaeroniscidae Stenoniscidae Tendosphaeridae Actaeciidae Armadillidae Armadillidiidae Atlantidiidae Balloniscidae Cylisticidae Eubelidae Periscyphicidae Porcellionidae Trachelipodidae Dubioniscidae Hekelidae Irmaosidae Pseudarmadillidae Scleropactidae

Woodlice (known by many common names; see below) are terrestrial crustaceans with a rigid, segmented, calcareous exoskeleton and fourteen jointed limbs. They form the suborder Oniscidea within the order Isopoda, with over 3,000 known species.

Woodlice in the genus Armadillidium can roll up into an almost perfect sphere as a defensive mechanism, hence some of the common names such as pill bug. Most woodlice, however, are not able to do this.

Ecology

Woodlice need moisture because they breathe through gills, called pseudotrachea, and so are usually found in damp, dark places, such as under rocks and logs. They are usually nocturnal and are detritivores, feeding mostly on dead plant matter. Woodlice then recycle the nutrients back into the soil. In artificial environments such as greenhouses where it can be very moist, woodlice may become abundant and damage young plants, such as ferns.

The woodlouse has a shell-like exoskeleton, which it must progressively shed as it grows. The moult takes place in two stages; the back half is lost first, followed two or three days later by the front. This method of moulting is different from that of most arthropods, who shed their cuticle in a single process.

A female woodlouse will keep fertilized eggs in a patch on the underside of her body until they hatch into small, pink offspring. The mother then appears to "give birth" to her offspring.

Some species of woodlice are able to roll into a ball-like form when threatened by predators, leaving only their armoured back exposed. This ability, or dominant behavior, explains many of the woodlouse's common names.

Metabolic rate is temperature dependent in woodlice. In contrast to mammals and birds, invertebrates are not "self heating": the external environmental temperature relates directly to their rate of respiration.

They are not generally regarded as a serious household pest as they do not spread disease and do not damage wood or structures, however their presence can indicate dampness problems.

Aquatic isopods

Although woodlice are terrestrial crustaceans, several forms have returned to water. Although most of these are amphibious, some have become truly aquatic.

Examples include some Haloniscus species from Australia (family Scyphacidae), and in the northern hemisphere several species of Trichoniscidae and Thailandoniscus annae (family Styloniscidae). Species for which aquatic life is assumed include Typhlotricholigoides aquaticus (Mexico) and Cantabroniscus primitivus (Spain) .

Common names

Common names for woodlice vary throughout the English-speaking world. A number of common names make reference to the fact that some species of woodlice can roll up into a ball. Other names compare the woodlouse to a pig.

Names include: "armadillo bug" , "cheeselog" (Reading, Berkshire) , "doodlebug" (also used for the larva of an antlion) , "pill bug" (usually applied only to the genus Armadillidium) , "roly-poly" , "potato bug", "roll up bug" , "slater" , "Carpenter", "Wood Bug", and "sow bug" .

In north Devon and north Somerset, England, a woodlouse is traditionally referred by the quaint name "Chuggy-peg", "Chuggy-pig" or "Chuggypig".

In Scotland, woodlice are commonly known as "slaters".

United Kingdom

There are 37 native or naturalised species in the United Kingdom, ranging in colour and in size (3–30 mm) of which only five are common: Oniscus asellus (the common shiny woodlouse), Porcellio scaber (the common rough woodlouse), Philoscia muscorum (the common striped woodlouse), Trichoniscus pusillus (the common pygmy woodlouse) and Armadillidium vulgare (the common pill bug). They are also called "wood bugs" and "slaters" in some areas.

Pillbugs and pill millipedes

Pillbugs (woodlice of the family Armadillidiidae) can be confused with Pill millipedes although they are only very distantly related to one another.

Both of these groups of terrestrial segmented arthropods are about the same size. They live in very similar habitats, and they can both roll up into a ball. Both pill millipedes and pillbugs appear superficially similar to the naked eye. This is an example of convergent evolution.

Pill millipedes can be distinguished from woodlice on the basis of having two pairs of legs per body segment instead of one pair like all isopods. Pill millipedes also have thirteen body segments, whereas the woodlouse has eleven. In addition, pill millipedes are smoother, and resemble normal millipedes in overall coloring and the shape of the segments.

Gallery

• 
  Porcellio scaber (left) and Oniscus asellus (center)
• 
  Armadillidium vulgare
• 
  Armadillidium vulgare rolled up
• Philoscia muscorum
  Philoscia muscorum

Fiction

• In To Kill a Mockingbird, the main character Scout pokes a "roly-poly".

• In the Pixar film A Bug's Life two supporting characters are acrobatic woodlice, "Tuck" and "Roll", who have their own ride at Disney's California Adventure Park.

• The giant creatures called Ohmu in Hayao Miyazaki's Nausicaä of the Valley of the Wind also resemble woodlice.

• In the webcomic Wigu, giant woodlice ("slagathors") are infrequently featured. They are forced to run organised races on alien planets.

• The Gustav, a mecha from the Zoids franchise, is similar in design to a woodlouse.

• In Harry Potter and Order of the Phoenix, woodlice are fed to bowtruckles.

• Dink Smallwood includes the woodlouse as an enemy.

• In a Rugrats episode, Chuckie Finster kept one as a pet, but it died a few days after. Its name was Melville.

• In Salad Fingers (an underground cartoon by David Firth) there was a woodlouse which was tragically flattened when Salad Fingers tried to pet her.

• Woodlice are part of the story in the movie Tierra by Julio Medem.

• In the film La métamorphose des cloportes, woodlice (cloportes) are a part of the title, and shots of woodlice appear during the opening credits.

• In Lexx, the Gigashadow resembles a gigantic, planet-sized woodlouse. The Lexx logo resembles a rolled-up woodlouse as well.

• In Rescue Rangers, Professor Nimnal uses his Giganto Gun to turn pillbugs into fake aliens for extorting gold as spaceship fuel.

See also

• Woodlouse hunter spider

External links

• Woodlice and Pill Bugs - diagnostic photographs
• BBC nature
• Video of Woodlouse in motion
• Raising woodlice in captivity

Further reading

• Christian Schmidt & Andreas Leistikow (2004). "Catalogue of the terrestrial Isopoda (Crustacea: Isopoda: Oniscidea)" (PDF). Steenstrupia. 28 (1): 1–118. {{cite journal}}: Unknown parameter |quotes= ignored (help) (all genera published until end of 2001)