Centipedes, Millipedes, Pauropods, Symphylans and Woodlice & Waterlice are Arthropods, all with segmented bodies bearing jointed legs and a hard exoskeleton.
Centipedes (Class Chilopoda) are recognised by having at least 15 pairs of legs (some immatures have fewer) with a single pair on each trunk segment. They also have large poison claws which are specially modified legs under the head (millipedes do not have these). Centipedes are generally considered to be carnivorous although this may not be true for all groups. More than 50 species, representing four orders of centipede, are found in Britain & Ireland.
Geophilomorpha (earth centipedes or wire-centipedes), with 25 British species are relatively long, often yellowish or pale (others are reddish-brown) and with 35 – 101 leg pairs. The three species of Scolopendromorpha have 21 leg pairs and are reddish brown, fast moving types. Lithobiomorpha (stone centipedes) are relatively stout, commonly chestnut or reddish brown and with 15 pairs of relatively long legs. There are 18 species in Britain, all in the genera Lithobius or Lamyctes. Representatives of a fourth order, the Scutigeromorpa (house centipedes) are sometimes found in buildings in mainland Britain and Scutigera coleoptrata occurs outdoors in the Channel Islands. These have very long legs and are usually with very distinct yellow and violet banding on their body and legs as well as compound eyes.
All millipedes can be distinguished from centipedes by the two pairs of legs on each body segment, and they lack the sharp 'poison claws' of the carnivorous centipedes. Millipedes are generally considered to be detritivores and many species do play an essential role in the breakdown of leaf litter. However, some could be considered scavengers and will feed on dead animal material. Other species are herbivores that graze on algae and lichens. A few species are considered agricultural or horticultural pests.
Symphylans and Pauropods
Symphylans resemble small, white centipedes with one pair of legs per body segment but they have only 12 pairs of legs in all and no poison claws. The British checklist currently includes just 14 species but the group have not been well studied. Mainly due to their small size they can be difficult to identify.
Pauropods are the smallest of the myriapods, just 1-2mm long. Few BMIG members have seen these animals in the field although very large densities have been reported from soil samples in some studies. Pauropods can be recognised by their branched antennae. All but one of the 23 species recorded from Britain have an elongate body form.
Woodlice and Waterlice
Woodlice and Waterlice belong to the Crustacean Order Isopoda, which means ‘equal feet’. This is a reference to their seven pairs of more or less identical legs. The body comprises 12 segments and is flattened from top to bottom to facilitate walking. Most Isopods are marine and the fossil record suggests that woodlice evolved from their marine ancestors relatively recently, to colonise dry land, around 50 mya.
Britain’s non-marine Isopods are divided into two sub-orders: Asellota, the Aquatic Waterlice, and Oniscidea, the Terrestrial Woodlice. Just four species of waterlouse, but 40 species of woodlouse are known to occur in the wild in Britain (Gregory, 2009). Woodlice and waterlice are detritivores, mainly feeding upon organic detritus, such as dead leaves, dead wood, etc. Some will also graze algae and fungi.
Landhopper - Arcitalitrus dorrieni
The Landhopper or Woodhopper is the only truly terrestrial anmphipod occuring in the British Isles. It is not native, but originates from Eastern Australia, and was first found in Britain early in the 20th Century. Arcitalitrus dorrieni has been adopted by BMIG as an "honorary woodlouse" to provide a focus for recording.