A pseudoscorpion, (also known as a false scorpion or book scorpion), is an invertebrate animal belonging to the order Pseudoscorpionida in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda. They are sometimes known as Pseudoscorpiones or Chelonethida.

Physical characteristics

Pseudoscorpion species Lasiochernes cretonatus
Photo Hans Henderickx

Pseudoscorpions are tiny, scorpion-like arthropods with a flat, pear-shaped body with two sections, eight 5-segmented legs, and simple eyes. The color of the body can be yellowish-tan to dark-brown, with the paired claws often a contrasting color. They have two very long pedipalps, or pincers, which strongly resemble the scorpion's claws, but the pseudoscorpion's abdomen is short and rounded at the rear, rather than extending into a segmented tail and sting.

They range from 2 to 8 mm (1/16 to 1/8 inch) in length.

The movable part of the pincer contains a venom gland and duct; the poison is used to capture and immobilize their tiny prey. They do not bite. To digest prey, they pour a mildly corrosive fluid over the prey, then ingest the liquefied remains.

They spin silk from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather.

Growth

During the elaborate mating dance, a male pulls a female over a spermatophore previously laid upon a surface. The female carries the fertilized eggs in a brood pouch attached to her abdomen, and the young ride on the mother for a short time after they hatch. Up to two dozen young are hatched in a single brood; there may be more than one brood per year. The young go through three molts over the course of several years before reaching adulthood. Adult pseudoscorpions live 2 to 3 years. They are active in the warm months of the year, overwintering in silken coccoons when the weather grows cold.

Pseudoscorpions are generally beneficial to humans since they prey on clothes moth larvae, carpet beetle larvae, booklice, ants, mites, and small flies. They are small and inoffensive, and are rarely seen due to their size. They usually enter the home by "riding along" with larger insects, or are brought in with firewood. They are often observed in bathrooms or laundry rooms, since they seek humidity. They may sometimes be found feeding on mites under the wing covers of certain beetles.

Geographical Distribution

There are more than 2,000 species of pseudoscorpions recorded, with more being discovered every day. They range worldwide, even in temperate to cold regions like Michigan in the United States, but have their most dense and diverse populations in the tropics and subtropics. Chelifer cancroides is the species most commonly found in homes. Other species have been found under tree bark, in leaf and pine litter, in soil, in tree hollows, under stones and within fractured rocks.