woodlice overview - woodlice body pattern - woodlice lifecycle - woodlice eating habits - woodlice used as medicine - native British and Irish woodlice - woodlice as pets - sexing woodlice
Porcellio scaber (above)
Above and below are woodlice, also known as sow-bugs or slaters, Order Isopoda. In the Crustacea phylum they are the only order that contain species that are wholly terrestrial. Although there are also freshwater (see Ascellus) and marine species.
There are over 4,000 species of isopods in the world. Most are small, although there is a deep sea giant aptly named Bathynomus giganteus, which can reach 42 cm long and 15 cm wide! The 37 species of British and Irish woodlice are listed below, but there are a few introduced species which can breed indoors only. Most range in size from 5 - 15 mm. Most are grey or grey/brown in colour. In the terrestrial species the animal's whole life revolves around the avoidance of desiccation. Therefore it is active mainly during the night. It is thought that isopods colonized the land during the Carboniferous.
In olden days woodlice were carried around in a small bag and used to treat stomach aches. As their exoskeleton is mainly calcium carbonate they may have been able to neutralize stomach acids and so treat ulcers, heartburn, and over indulgence in general.
Below, a diagram showing
how to tell the difference between male and female woodlice.
At the top of the page you can see the underside of a terrestrial woodlouse, they have 7 pairs of walking legs. The first pair of antennae are usually short, and in terrestrial species they are often vestigial. The second pair of antennae are usually well developed, except in the parasitic species. To tell the difference between adult male and female woodlice see the diagram above. Woodlice are preyed upon by spiders, toads, and centipedes. Most woodlice have a series of glands running down the sides of their body which release a sticky, foul fluid when the animal is attacked. This helps it repel and escape from predators.
There is not much in the way of woodlice courtship; just the male tapping the female with his antennae. The female carries her eggs and young in a fluid-filled pouch on her underside, and it takes about two years for the young to reach maturity. On release from the female's brood pouch the young woodlouse has 6 pairs of legs. Within 24 hours it will moult, and the 7th segment which will bear legs appears. After the next moult it will have the full compliment of 7 pairs of legs.
Moulting is a process of two halves; the hind part is cast off a few days before the front part, as can be seen in the photograph of Porcellio scaber.
Very few woodlice live longer than 2 - 3 years, however in California, where the common pill bug Armadillidium vulgare was introduced just over 100 years ago, it lives for 4 years, and females can have 3 or 4 broods.
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UK woodlice (and most others) feed mainly on rotting vegetation, algae, bacteria, fungi and animal remains and so help to return valuable nutrients to the soil. Woodlice rarely eat living plants, so gardeners should not consider them pests. However they do take an occasional nibble of seedlings in greenhouses and cold frames. On the whole they do much more good than harm, and are especially useful in chewing up plant fragments in compost heaps, and their faeces aids decomposition. Although UK woodlice are vegetarian, there are a few others that are not. There is one (Scyphax ornatus) in New Zealand which lives on sandy beeches, and specializes in eating drowned honey bees. And in the USA woodlice are used in museums to clean the flesh off vertebrate skeletons.
Woodlice are fairly easy to keep as pets at home or in the classroom. Plastic containers make the easiest housing. And all that is needed to keep them happy is a layer of soil, a piece or two of bark, and perhaps a stone and some dead leaves.
A small piece of carrot or other vegetable can be added once a week. Spray with water occasionally to keep conditions humid. It is important not to make conditions too wet or too dry. One of the ways to do this is to spray just the one part of the box. In fact if you have a large box and different species of woodlice this can be used to study the differences in species preferences.