1. Distribution

2. Description

3. Habitat

4. Feeding

5. Life cycle

6. Behaviour

7. Algorithm

8. See also

9. References

10. External links

Porcellio scaber (otherwise known as the common rough woodlouse or simply rough woodlouse), is a species of woodlouse native to Europe but with a cosmopolitan 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.

Distribution

Description

P. scaber has an oval body, can grow up to {{convert|20|mm|inch}} long, and is usually a grey colour, paler underneath, although brown, blue, yellow, or pinkish hues may also be observed (like many other woodlice, a red variety can often be found in coastal areas{{Citation needed|date=August 2018}}). The dorsal (upper) surface of its segmented exoskeleton is covered in a series of small tubercles hence its common name.

At the head it has two pairs of antennae, with the inner pair being very small. Two compound eyes are located on the dorsal side of the head, while the mouth parts are on the ventral (lower) side.

There are 7 pairs of legs, corresponding to the 7 segments of the thorax. The short abdomen consists of 6 segments.^[5] 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 are is a small telson flanked by a pair of appendages known as uropods.^[5]

Habitat

Feeding

P. scaber is a detritivore - it mainly feeds on decaying leaf litter but will consume any rotting plant matter. Living plants are of limited nutritional value for these woodlice which prefer to feed on the bacteria and fungi which cause decay.^[7] P. scaber has very sensitive olfactory receptors that allow it detect the smell of microbial activity and so locate food.^[8] This ability to quickly detect the faintest sign of decay has led to the false{{Citation needed|text=false|date=August 2018|reason=}} belief that they harm seedlings and soft fruit.

Life cycle

25 to 90 fertilized eggs and the larvae are carried by the mother in a fluid-filled sac at the ventral side of the abdomen for about 40-50 days. The young are fully grown after 3 months; the adult animals have a life expectancy of about two years.^[5]

Behaviour

P. scaber respond to certain stimuli with kinesis behaviour. 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 (including P. 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 a Petri dish is unwilling to move into the center of the dish, preferring to stay near the edge.

Another reflex exhibited by P. 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 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.^[9]

Unlike the 'roller' species of woodlouse, such as Armadillidium spp., which are able to curl into a ball to defend themselves, P. scaber is a 'clinger' and adopts a posture of tonic immobility when faced with the threat of predation. A study of this thanatosis behaviour found that individuals of this species had unique personalities with shy woodlice staying still for longer and bold woodlice staying immobile for less time.^[10]

Algorithm

Inspired by the behaviours of P. scaber, an algorithm for solving constrained optimization problems was proposed, called the Porcellio scaber algorithm (PSA).^[11][12]

See also

• List of woodlice of the British Isles

References

External links

• {{Commons category-inline|Porcellio scaber}}
• Woodlice Online

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