Isopoda - Woodlice, aquatic species, etc.
Crustacea (water fleas, cyclops, barnacles, crabs, shrimps, etc.)
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Above is Porcellio laevis, a rather rare species which is a smooth and glossy brown-grey. It reaches 18 mm when fully grown. Its eyes consist of a number of black ocelli. It is found in gardens and compost heaps in eastern and southern England, and around Dublin in Ireland. There are no records from Wales or Scotland.

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 and marine species. There are over 4000 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! 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 colonised the land during the Carboniferous.

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.

The female carries her eggs and young in a fluid-filled pouch beneath her, and it takes about two years for the young to reach maturity.

There are 37 species of woodlice native to the British Isles (see the list), but there are a few introduced species which can breed indoors only. Most range in size from 5 - 15 mm. 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. Very few woodlice live longer than 2 - 3 years, however in California, where the common pill bug Armadillidum vulgare was introduced just over 100 years ago, it lives for 4 years, and females can have 3 or 4 broods.

UK woodlice (and most others) feed mainly on rotting vegetation, 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 specialises in eating drowned honey bees. And in the USA woodlice are used in museums to clean the flesh off vertebrate skeletons.

They can exude a repellent secretion from their rear end to warn off predators.

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 neutralise stomach acids and so treat ulcers, heartburn, and over indulgence in general.

Woodlice are preyed upon by spiders, toads, and centipedes.

Left is Porcellio scaber can tolerate drier places, and is slate grey, but nearer the coast orange, cream, black and red speckled morphs have been found. It is 17 mm long and 8.5 mm wide when fully grown, and is very common in the U. K. and is also found in Western Europe, Iceland, South America, and South Africa. It is covered in tubercles (bumps), and its exoskeleton is not shiny at all. This one has just moulted. Unlike insects they do not moult their whole exoskeleton at once, but in two parts. They can moult up to 25 times. It often enters houses

Androniscus dentiger, the rosy woodlouse, right has large eyes, long antennae, and is pink, red or white with 2 long yellow lines running down its body. When fully grown it reaches 6 mm long. It is usually found in caves and mines or among garden rubble and quarries. It moves quickly when disturbed. As well as the U. K. it is found in Germany, Holland, Finland, what used to be Yugoslavia, North Africa and Canada.

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