Worldwide there are estimated to be 8,000 species of centipede of which 3,000 have been described. Centipedes have a wide geographical range, reaching beyond the Arctic Circle. Centipedes are found in an array of terrestrial habitats from tropical rainforests to deserts. Within these habitats centipedes require a moist micro-habitat because they lack the waxy cuticle of insects and arachnids, and so lose water rapidly through the skin. Accordingly, they are found in soil and leaf litter, under stones and dead wood, and inside logs. Centipedes are among the largest terrestrial invertebrate predators and often contribute significantly to the invertebrate predatory biomass in terrestrial ecosystems.