Talk:Porcellio scaber

Roly-Poly
In the South, we also refer to these as roly-polies because they roll up into a perfect little ball when uncovered.

-This species doesn't roll up at all, only Pill woodlice do.

IceDragon64 (talk) 23:17, 14 July 2014 (UTC)

Text dump of high-school level assignment about P. scaber
Released under the GPL for editing in the article. Ppe42 / L Howison, Wellington, New Zealand.

Taxonomy and general facts should be useful, some original research not so much.

Animal Study of Porcellio scaber

Family	 Porcellionidae These are woodlice that have an exoskeleton that extends over their legs (an overhang). Their uropods are spear shaped and flattened, and extend beyond the telson (fused tail segments). Despite their appearance, these woodlice cannot roll into a ball.

Genus	Porcellio The heads of Porcellio have tri-lobed heads: two definite outer lobes and a central, almost triangular lobe.

Species scaber This species is generally slate grey all over (apart from variations due to moulting and age) with the head being the same colour as the body, while some other species have quite interesting colour schemes. The head and back (dorsal surface) of Porcellio scaber is covered in small wart-like nodules. Also, Porcellio scaber lacks a median stripe on its back.

�Introduction: General Woodlice Information

The common woodlouse, Porcellio scaber, is a small terrestrial crustacean that mostly inhabits terrestrial soil, helping decompose plants and animal matter.

Although woodlice resemble insects, being a small animal with segmented legs and a rigid exoskeleton, it is not an insect. One difference is in the seven pairs of legs (insects have six). Also, woodlice breathe through modified gills (thanks to their aquatic crustacean ancestors) whereas insects use trachea to transport oxygen directly to the tissues.

Woodlice move about on their legs (pereiopods) which are spread far apart under the body, giving them great stability. The legs are also quite long to give the animal speed while running. They can move directionally (taxis) for some purposes, and wander randomly (kinesis) for others. Woodlice reproduce sexually, with the male fertilising the females eggs. The young grow in a brood pouch, growing in an egg-like structure for about a month, then hatching out and remaining in the brood pouch for a few days. After they are born the woodlice are capable of looking after themselves, but are not fully mature until they moult twice and gain the full set of segments and legs. Thereafter they must moult periodically to shed the rigid exoskeleton so they can grow larger.

Woodlice have various sensing organs: the compound eyes, movement and chemical sensors, and humidity sensors, possibly on the antenna. As woodlice are somewhat obscure, they have not yet been extensively studied and some sensor-like structures have not yet been identified.

Woodlice eat decaying plant matter, fungal spores, live plants, and their own faeces. Their liking for very young plants has led to them being a nuisance in some nurseries, but this is the only occasional when woodlice are pests, and they are easily controlled by pesticides as they do not develop resistance easily.

Undigested food is excreted in the form of faeces, and nitrogenous waste as ammonia gas, which the animals have a high resistance to. Although water is saved from urine, it is used by the permeable cuticle (required for ammonia excretion).

�Life Cycle

The woodlice life cycle is relatively simple because the animal does not require any parental care. After conception it develops from an embryo into a young woodlouse, which can live on its own. Two moults later it is mature and ready to start the life cycle again.

Mating

When a male woodlouse comes across a receptive female, he stops, waves his antenna and then places them on the female. If she does not turn away he climbs onto her back and licks her head with his mouthpieces while tapping her back with his front legs. This goes on for several minutes. Then the male shifts diagonally across the female’s back, bends his tail under her and transfers sperm from his stylets (part of his genital pores on the pleopods) into her genital pore. After a few minutes this is complete and he can turn and repeat the operation on the other side.

Conception

The female has formed a brood pouch during the moulting prior to mating. The brood pouch is a fluid-filled space made between the females belly and a layer of overlapping plates called oostegites. Inside the female’s genital pores the eggs are fertilised by the sperm, and then pass through oviducts into the brood pouch.

Embryology

The eggs are initially a mass of yolk inside two membranes. The actual cells divide and grow from 1 to 2, to 4, to 8, to 16 cells over a few days, while migrating to the outside of the yolk mass. From here the mass of cells begins to differentiate and show signs of segmentation. By the 17th day, buds of limbs are present and organs have begun to form. The embryo has by now gradually increased in size until it bursts one of the membranes. The rest of the yolk passes into the digestive system and the head begins to form. By the 21st day, the body can move slowly. The woodlice embryo straightens out inside the membrane so it can grow larger. By the 26th day, the woodlice embryo has darkened, indicating that the cuticle has formed. The yolk has run out and the eyes have become pigmented. Movement increases until the membrane ruptures. The young now live inside the brood pouch for several days, and fluid in the pouch gradually disappears.

Birth

When the young are ready they simply crawl out of the brood pouch.

Maturation

At first the young woodlice have only 6 thorax segments, but after their first moult they have seven. After the second moult this segment also has legs, and the woodlice is mature. Subsequent moultings do not change its physiology.

�Special Features of Porcellio scaber

A woodlouse’s modified gills lose water very quickly, as does the rest of the body surface. Also, their faeces are quite watery. If the creature dries out it cannot function properly and will die. For this reason, they have evolved several behaviours that ensure they can acquire more water and inhabit only sufficiently moist environments that can prevent them from drying out (desiccation). Firstly they consume water through food and drinking, and by anal drinking, which is actually capillary action. This involves pressing the uropods against a moist substrate; water moves by capillary action through channels to wet the underside of the woodlouses body. Also, water may be absorbed through the cuticle if the animal is immersed in water, as in rain. Also, they prefer dark moist crevices, which both shelter them from the sun and protect the woodlice from predators. Shelter from the sun and its associated warmth is important; at a similar humidity, thirty degrees has a much greater drying action than ten degrees. Conversely, woodlice can also be too wet: saturated with water. This could occur by prolonged exposure to a very moist environment, or in rainy conditions. Woodlice in these conditions will seek a dry environment. They can lose water by reverse capillary action (anal drinking); water can pass out of the body if the substrate is dry enough. Also, the woodlice may be able to add water to the gut contents to increase water in the faeces.

The permeability of the cuticle, which restricts the animal to damp environments, may be necessary because of the excretion of ammonia gas through the cuticle. The advantage is probably due to the energy saved by not converting the ammonia into urea or uric acid.

Woodlice must moult because their hard exoskeleton, which provides protection and waterproofing to some extent, is not flexible enough to grow with them. Therefore the woodlice must periodically shed this exoskeleton. A few days before moulting, the woodlice becomes inactive and stops feeding. When the rear half of the body is ready, the skin splits and the animal pulls itself out using the front legs. A few days later the same process occurs with the front half. Often the cast skin is eaten. The woodlice can now grow before its new exoskeleton hardens. In captivity, they may be subject to cannibalism by other woodlice while moulting, but his probably does not occur in the wild.

Woodlice eat decaying plant matter, fungal spores, live plants, and their own faeces. Their liking for very young plants has led to them being a nuisance in some nurseries, but this is the only occasional when woodlice are pests, and they are easily controlled by pesticides as they do not develop resistance easily.

Woodlice have a very large requirement for copper which is due to their blood pigment hemocyanin which contains copper just as haemoglobin contains iron. Curiously, woodlice seem to require even more than is necessary for that purpose. It seems that they eat their own faeces because, although their food contains plenty of copper, it is not digestible until changed into a digestible form by bacteria in the faeces.

�Bibliography

Websites:

http://www.geocities.com/CapeCanaveral/Hangar/7649/wlice.htm Woodlice Online, Greg McKenzie. Last updated: 19/04/00

Books:

Allan, Richard, and Greenwood, Tracey. Year 13 Biology Student Resource and Activity Manual 2000. Biozone International, Ltd, 1999.

Sutton, S.L. Woodlice. Ginn & Company, 1972.

Resources:

Form Seven Biology Slater Study, New Zealand Correspondence School. —Preceding unsigned comment added by Ppe42 (talk • contribs) 11:02, 26 March 2008 (UTC)

- This material is mostly a description of woodlice in general and I question various parts - Many woodlice reproduce assexually as well as sexually, for example.

IceDragon64 (talk) 23:21, 14 July 2014 (UTC)