Single or double legs
This group of arthropods are decided into centipedes and millipedes. Centipedes have one pair of legs on each body segment and millipedes have two pairs of legs per segment.
Appearance and characteristics
Millipedes have most legs in relation to body length - between 22 (11 pairs) and 750 (375 pairs). Younger, not yet mature, animals have fewer segments and also have fewer legs than adults. Millipedes are mainly slow, peaceful herbivores, but they can also feed on dead organic matter. If they feel threatened, they roll themselves into a tight spiral. The back cover's hard shell protects the softer abdominal side. The centipedes, on the other hand, are fast predators that kill their prey with a venomous bite. In crosssection, the double-legged body is highly arched, while the single-legged body has a slightly arched (flattened) body shape. Most myriapods are night-active because they are sensitive to dehydration. Therefore, they also often search for humid environments. They are not easy to spot because they usually live a bit down in the soil layer or beneath the bark of decaying trees. Because they are long, narrow and flexible, they can squeeze themselves into tight spaces with the help of their many feet.
The African giant centipede (Archispirostreptus gigas) is one of the very largest millipede. It can grow 38.5 cm long. The smallest Swedish double footing is the the bristly millipede Polyxenus lagurus, which is only 3 mm long. The longest Swedish species is the striped millipede Ommatoiulus sabulosus, which can grow to 47 mm in length. A South American centipede (Scolopendra gigantea) grows up to 30 cm long and can kill frogs, lizards and mice. The around 40 species that occur in the Nordic countries are considerably smaller and are harmless to humans.
Myriapods breath, like insects and many spiders, with tracheas. The trachea system transports oxygen and carbon dioxide all the way between the surrounding air and the body cells. This air tube system is indentations from the skin and consists just like this of chitin. Usually there are two holes (spiracles) for air passage on each side of all body segments.