an order of arthropods of the class Arachnida. They are from 1 to 10 mm long. The cephalothorax is covered with a chitinous carapace; on its anterior are the eyes, the mouthparts, a pair of clawlike chelicerae, and a pair of pedipalpi. The pedipalpi end in well-developed chelae similar to the chelae of scorpions (hence the name “pseudoscorpions”). Some pseudoscorpions have chelae with poison glands. The sexes are separate.
There are approximately 1,100 widely distributed species. Many different species are particularly numerous in the tropics. Pseudoscorpions live concealed beneath moss, fallen leaves, stones, and bark, as well as in animal burrows and nests, anthills, and wasp nests. They are also found in human dwellings (often in libraries) and livestock shelters.