| Porcellio scaber | |
|---|---|
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| P. scaber, head is left | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Isopoda |
| Suborder: | Oniscidea |
| Family: | Porcellionidae |
| Genus: | Porcellio |
| Species: | P. scaber |
| Binomial name | |
| Porcellio scaber | |
| Synonyms | |
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Porcellio scaber (otherwise known as thecommon rough woodlouse or simplyrough woodlouse), is a species ofwoodlouse native toEurope but with acosmopolitan distribution. They are often found in large numbers in most regions, with many species (shrews, centipedes, toads, spiders and even some birds) preying on them.
One subspecies,Porcellio scaber lusitanus, is currently recognized. Two other subspecies were historically deemed valid but are no longer recognized.P. s. americanus, described in 1932,[2] was considered endemic in theAmericas.P. s. japonicus was described in 1928 and believed to be endemic toJapan.[3] Both subspecies were synonymized with thenominate in 2020.[4]
Porcellio scaber is found acrossCentral andWestern Europe.[5] In theUnited Kingdom, it is one of the "big five" species of woodlice. It has also colonisedNorth America,South Africa and other regions including the remotesub-AntarcticMarion island, largely through human activity.[6] It is also the most common species of woodlice found inAustralia.[7]
Porcellio scaber has an oval body, can grow up to 20 millimetres (0.79 in) long, and is usually a grey colour, paler underneath, although, brown, blue, yellow, orange, or pinkish hues may also be observed. Thedorsal (upper) surface of its segmented exoskeleton is covered in a series of smalltubercles hence its common name.
At the head it has two pairs ofantennae, with the inner pair being very small. Two compound eyes are located on the dorsal side of the head, while the mouthparts are on the ventral (lower) side.
There are 7 pairs oflegs, corresponding to the 7 segments of the thorax. The short abdomen consists of 6 segments.[8] On the ventral side of the abdomen there are two whitish pseudo-lungs, connected with pores to the outside air. At the rear end there is a smalltelson flanked by a pair of appendages known asuropods.[8]
Porcellio scaber loses water by diffusion through its permeableexoskeleton which lacks a waxycuticle. Because of this, to avoiddesiccation, it often seeks out environments with humid air and plenty of ground moisture, preferably cold to minimize rate of water loss, and dark to avoid detection by predators. It lives in a wide variety of damp habitats but it is less dependent on high levels ofhumidity thanOniscus asellus.[9]
Porcellio scaber is adetritivore – it mainly feeds on decayingleaf litter but will consume any rotting plant matter. Living plants are of limited nutritional value for these woodlice which prefer to feed on thebacteria andfungi which cause decay.[10]P. scaber has very sensitiveolfactory receptors that allow it detect the smell of microbial activity and to locate food.[11]
The females carry about 25 to 90 fertilized eggs until they hatch and are held in a fluid-filled sac at the ventral side of the abdomen for about 40–50 days. The young are reproductively mature after 3 months; the adult animals have a life expectancy of about two years.[8]
Porcellio scaber respond to certain stimuli withkinesis behaviour.[12] To attempt to find an environment where they lose less moisture and then stay there,P. scaber alter factors such as speed and rate of turning (orthokinesis and klinokinesis). When in a dry or hot environment, these woodlice have been observed increasing speed and turn more often in an attempt to leave the unfavorable environment. In a moist, dark, cool environment, they slow down dramatically and often stop altogether. To avoid desiccation, most woodlice (includingP. scaber) exhibit thigmokinesis, slowing down or stopping when in contact with multiple surfaces (such as the corner of a box or a crack between two bricks). This behaviour leads to clumping of woodlice, reducing the exposed surface area through which water can be lost. Another manifestation of this is that a woodlouse in aPetri dish is unwilling to move into the center of the dish, preferring to stay near the edge.
Another reflex exhibited byP. scaber is turn alternation. During klinokinesis, turns alternate between left and right. This helps the woodlouse escape from a harmful environment or predator more efficiently as alternating turns average to form a straight line, unlike random turns which may well become a circle back to the predator. Several mechanisms for this have been proposed, such as short-term memory or following the outside wall, but the theory with most support is the bilateral asymmetrical leg movement (BALM) mechanism, which suggests that on the original turn, the legs on the outside of the turn become relatively more tired, so end up being overpowered by the legs on the inside of the turn, causing it to turn the opposite way from last time.[13]
Unlike the 'roller' species of woodlouse, such asArmadillidium spp., which are able to curl into a ball to defend themselves,P. scaber is a 'clinger' and adopts a posture oftonic immobility when faced with the threat of predation. A study of this thanatosis behaviour found that individuals of this species had uniquepersonalities with shy woodlice staying still for longer and bold woodlice staying immobile for less time.[14]
Inspired by the behaviours ofP. scaber, an algorithm for solvingconstrained optimization problems was proposed, called the Porcellio scaber algorithm (PSA).[15][16]
Media related toPorcellio scaber at Wikimedia Commons
Data related toPorcellio scaber at WikispeciesAuthority control databases: National |
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