Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Isopoda
Suborder: Oniscoidea
Family: Porcellionidae
Genus: Porcellio
Species:scaber
Scientific name: Porcellio scaber
Common Names: Woodlice (plural), Woodlouse, slater,
The family Porcellionidae cannot roll into a ball, as opposed to the species of family Armadillidiidae, which can. This family contains 530 species in 17 genera, found on every continent except Antarctica. 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, although they have been known to feed on cultivated plants, such as ripening strawberries and tender seedlings. Woodlice then recycle the nutrients back into the soil.
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, which shed their cuticle in a single process. A female woodlouse will keep fertilised eggs in a marsupium on the underside of her body until they hatch into small, white offspring. The mother then appears to "give birth" to her offspring. Some species of woodlouse are able to roll into a ball-like form when threatened by predators, leaving only their armoured back exposed. ( not the Porcellio scaber in the photos).
Woodlice do not produce urine. instead of excreting urine they excrete their nitrogenous waste in the form of ammonia gas. Most animals find ammonia to be too toxic for excretion and so any ammonia formed is normally converted to urea or uric acid for excretion. Woodlice seem to have very high resistance to ammonia and are able to excrete it as a gas directly through the surface of their exoskeleton. This means that they do not need to use energy to convert the ammonia to urea or uric acid before excretion.
Woodlice have blue blood because along with most other crustaceans they have the compound haemocyanin in their blood. Haemocycanin carries oxygen in the same way that haemoglobin does in mammals. Haemocycanin contains a copper atom instead of the iron atom found in haemoglobin. The blood is pale blue when it is carrying oxygen. Because a woodlouse contains very small amounts of haemocycanin it is not possible to see these colour changes by direct observation.
Woodlice, like many other animals, eat their faeces. In the case of woodlice, this helps them to reabsorb sufficient copper minerals which have been lost in their faeces. Bacterial action on the faeces probably changes the copper to a form which is more easily absorbed into their bodies. Coprophagy is the term used to refer to the eating of faeces.
Drinking through the anus Woodlice get water with their food. But they can also drink it through their mouthparts and also by using their uropods. The uropods are tube-like structures on the posterior (back end) of the animal. When they use them for drinking they press their uropods close together and touch it against a moist surface. Capillary action pulls the water up the uropods and into the anus.
Woodlice also seem to be able to absorb water vapour directly through their exoskeleton surface in regions of high humidity, and in fact, if they remain in high humidity regions for too long they appear to become waterlogged and then tend to move to areas of lower humidity.
For more detailed information on its taxonomy visit http://www.porcellio.scaber.org/woodlice/taxonomy.htm
Photo of Porcellio scaber
Photo of a Porcellio scaber and cockroach egg cases to show their comparative size
[1]
A colour form found in a worm farm.
[2]
Photo of juvenile Porcellio scaber[3]
