#pseudoscorpiones

Pseudoscorpions are very small, often being overlooked or mistaken for ticks or spiders. They usually range from 2 to 8 mm (0.08 to 0.31 in) in length. The largest known species is the critically endangered Giant Pseudoscorpion (Garypus titanius) at up to 12 mm (0.5 in). It is native to Ascension Island in the South Atlantic Ocean, where it lives among seabird colonies, and feeds on smaller prey such as insects at night. It is endangered due to the introduction of nonnative predators to Ascension Island, such as mice and larger insects, and is now restricted only to Boatswain Bird Island, a smaller rocky island off Ascension Island.

As stated above, members of the clade Iocheirata are venomous, with a venom gland and duct usually located in the mobile finger of the chelae. The venom is used to immobilize the pseudoscorpion's prey, and is medically insignificant to humans. Along with scorpions and spiders, these are the only arachnids to produce venom. However, all three orders have different means of delivering the venom: scorpions through their telson (“tail”), pseudoscorpions through their chelae (“pinchers”), and spiders through their chelicerae (“fangs”), meaning that venom convergently evolved three separate times within the Arachnida class.

Venom is not the only trait pseudoscorpions convergently evolved with spiders; they can also spin silk from a gland in their jaws to make disk-shaped cocoons for mating, molting, or making “sleeping bags” for waiting out cold weather!

Similar to scorpions, members of the superfamily Cheliferoidea (Atemnidae, Cheliferidae, Chernetidae, and Withiidae) have an elaborate mating dance, which ends with the male navigating the female over his spermatophore.

Females will carry her fertilized eggs in a brood pouch attached to her abdomen. Between 2 and 50 baby pseudoscorpions are hatched in a single brood, with more than one brood per year possible. The young go through three molts called the protonymph, deutonymph, and tritonymph. The developing embryo and the protonymph, which remain attached to the mother, are fed with a “milk” produced by her ovary. Many species molt in a small, silken igloo that protects them from predators during this vulnerable period.

Pseudoscorpions are often phoretic, using larger animals (especially flying insects) as a form of transport to new environments.

Pseudoscorpions are generally beneficial to humans because they prey on species humans consider pests, such as clothes moth larvae, carpet beetle larvae, booklice, ants, mites, and small flies. They are beneficial to other animals as well, as many of them are known to feed on parasites. Many pseudoscorpion species co-exist with packrats, and two of them are known to feed on packrat ectoparasites, to mutual benefit. Some pseudoscorpions have been found feeding on mites under the wing covers of certain beetles.

The House Pseudoscorpion (Chelifer cancroides) is the most widely distributed species of pseudoscorpion in the world and occurs in a range of habitats, and is the species most commonly found in homes, where it is often observed in rooms with dusty books. They enter homes by riding insects (phoresy) larger than themselves or are brought in with firewood, and survive on common household invertebrates such as booklice and house dust mites.