Book Scorpion (Pseudoscorpion)

Order Pseudoscorpiones — the pseudoscorpions or false scorpions — contains about 3,400 species worldwide and is one of the most ancient surviving arachnid orders, with confirmed fossils dating to approximately 390 million years ago. Despite the close resemblance to true scorpions (pincer-bearing pedipalps, eight legs, segmented body), pseudoscorpions are anatomically and ecologically distinct: they have NO tail and NO sting (the pincer pedipalps deliver the venom, by injection from venom glands in the pedipalp 'fingers'), they are tiny (most species 2-8 mm), and they are silk-spinners (silk glands in the chelicerae produce silken disc retreats for moulting and overwintering). Chelifer cancroides — the book scorpion — is the most cosmopolitan pseudoscorpion species and one of the most-encountered indoor arachnids you've never noticed: she lives in the spaces between book pages, behind picture frames, in old paper files, and in the dust of attic and basement spaces, where she hunts booklice (Liposcelis), dust mites (Dermatophagoides), and other tiny indoor arthropods. The species is therefore a beneficial 'library pest' that consumes the actual library pests. Pseudoscorpions disperse via PHORESY: they grasp the leg of a much larger insect (flies, beetles, bees, and even the legs of harvestmen) and ride passively to a new habitat. The behavior is universal across the order and one of the most-cited examples of arthropod hitchhiking. Pseudoscorpions are completely harmless to humans — too small to bite or sting and entirely focused on much smaller prey.