The Centipedes and the Millipedes are nearly all long and slender animals with many body segments and numerous legs. They were once lumped together into a single group known as the Myriapoda. This name means 'many feet' and it was a very apt one for these animals. It is still quite a useful term although it is now realised that the centipedes and millipedes are not closely related and they are now put into their own separate classes. The centipedes belong to the class Chilopoda and the millipedes belong to the class Diplopoda. There are many differences to the habits of these two groups, but the most obvious is in the arrangement of the legs: centipedes have one pair of legs on each body segment, whilst millipedes have two sets of legs on nearly every segment.
Centipedes are all relatively slender animals, several or many times longer than they are broad. The British species range from 5 mm to about 70 mm in length and their colours vary from pale yellow through to deep brown. Their bodies are always distinctly flattened. Although, like all arthropods, the centipedes are covered with a tough outer coat, they lack a waterproof layer and they are confined to moist areas where there is no danger of drying up. Many live in the soil and leaf litter, while those that hunt freely on the ground are strictly nocturnal and spend the day hiding under logs and stones where they can keep moist. Like the Woodlice, they react strongly to touch and they do not normally come to rest unless both upper and lower surfaces are in contact with the surroundings. Such behaviour ensures that the animals end up under stones or bark, where they can be sure of moisture. The centipedes have not been studied to the same extent as have the woodlice, but it is likely that the two groups react in much the same way to light and humidity.
The centipedes head is quite flat and covered with a round or oval shield. It carries a pair of prominent antennae, which are the animals major sense organs, enabling it to smell and feel it's way around. Many of the species are quite blind, but some carry a number of simple eyes on the front of their head shield. Even so, with a few notable exceptions, their eyesight is very poor. The underside of the head bears a pair of stout jaws and two pairs of accessory jaws or maxillae, which hold the food whilst it is being chewed. Curving around the sides of the head are a pair of stout poison claws with which the centipede catches and kills it's prey. The poison produced by these claws is very strong and some of the large tropical centipedes can give a man a very painful and sometimes dangerous bite. Our British species however, are quite harmless, because they are all small and rarely able to pierce the skin.
The poison claws are attached to a collar-like segment just behind the head. This segment is followed by the leg-bearing trunk segments, of which there are between 15 to 101 in the British centipedes. The exact number varies from species to species and often within a species as well, but it is always an odd number. The upper and lower surfaces of each trunk segment are covered by protective shields, the upper ones of which are called tergites. Many of our centipedes exhibit a striking alternation between long and short tergites along the body, an arrangement which maintains the rigidity of the body when running at speed. Many of the trunk segments have a tiny pore or stigma on each side. These pores are the openings of the breathing system. They lead to minute tubes called tracheae, which spread throughout the body carrying air to all parts.
As a result of the number of trunk segments, centipedes do not have a 100 legs as the name suggests: there are between 30 and 202 in a fully equipped adult specimen (unless he's been run over by a lawnmower). The centipede has a problem controlling so many legs when moving about, but the problem is eased in many species because each leg is slightly longer than the one in front. With this arrangement, the centipede is less likely to trip over it's own feet. The last pair of legs is always slightly different from the rest and usually trails behind the body. These legs are well supplied with sensory bristles and they act as an extra pair of antennae. This is a very useful feature for animals whose hind quarters are some way from the head and which often need to back out of crevices.
The centipede is basically a predatory beast, although one of our garden species occasionally nibbles roots. They use their speed to run down and catch a variety of other creatures, including woodlice, harvestmen, spiders, mites, springtails, beetles, and many other insects. They also eat worms and slugs. This diet shows very clearly the problem of trying to organise any bio-system into 'friend' and 'foe'. By eating slugs and leatherjackets the centipedes are certainly doing the gardener a favour, but how much of this favour is undone when the centipede starts eating the garden spiders...difficult to answer...for the same reason, it is not practicable to go dousing every insect you see with insecticide...you never it was probably doing YOU a favour...until YOU clobbered it.
Their speed and their poison claws give the centipede an effective defence against most of their enemies, and little is known about the animals which may eat centipedes. Birds, including domestic chickens, eat centipedes when they can catch them, and so do shrews and toads. Ground beetles, spiders and harvestmen probably take appreciable numbers of centipedes when they are at their young stage in life, but the most important predator of a centipede is another centipede. Injured specimens are readily eaten in captivity, and their cannibalistic tendencies ensure that one rarely finds more than a single centipede under one stone.
Again little is known about their reproduction. The females lay their eggs throughout the spring and summer, but the eggs are rarely found. Those of many species are sticky and they are rolled in the soil as soon as they are laid, thus making them almost impossible to find. Other species actually look after their eggs and young for a while. The way in which centipedes grow up differs from species to species and will be covered as each separate species is explained. Several moults or skin changes are necessary however, and these give the centipede the chance to replace legs which have been lost. Centipedes are often seen with one or more legs shorter than the others. The short legs are being regenerated and they get larger with every moult. If a centipede loses a leg when it is very young it can regenerate another. If the leg is lost in later life, there may not be enough moults left in it's life to totally regenerate the leg, therefore it will always have a shorter leg....hence the joke....What goes 99 clunk?..A centipede with a wooden leg...ha...ha...ok, please yourself..!
The centipedes are basically a tropical group and, as far as I know, only 44 have been recorded in he British Isles. Even then, not all these are natives of our islands. Several species have been brought in with plants and have succeeded in establishing themselves (as is the case with a lot of animals in this country). These introduced species are usually listed as synanthropic ('with man'), in that they are rarely found away from human activity, but they are generally restricted to localised areas near the original point of entry, unless of course, they become fully acclimatised, then they will be able to spread further afield. Only about a dozen species are what can be called common and widely distributed. They can be found at all times of the year, but they are most numerous in spring and autumn, you've only got to dig the garden over to find them. During the winter and the drier parts of the year the animals burrow down into the soil where they are less affected by the cold and drought.
