A pseudoscorpion, (also known as a false scorpion or book scorpion), is an arachnid belonging to the order Pseudoscorpionida, also known as Pseudoscorpiones or Chelonethida.

Physical characteristics

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Pseudoscorpions are small, 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 stinger.

They range from 2 to 8 mm (1/12 to 1/3 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. Another trait they share with their closest relatives, the spiders, is that they breath through spiracles. Most spiders have one pair of spiracles, and one of book lungs, but pseudoscorpions only have the former; a single pair of spiracles.

Geographical Distribution

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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 and above timberline in Wyoming's Rocky Mountains 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, in caves, at the seashore in the intertidal zone, and within fractured rocks.

Evolution

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Until recently, the oldest pseudoscorpion fossils known were only 35 million years old, but some have now been found dating back over ten times as far, 380 million years, to the Devonian period, near the time when the first land-animal fossils appear. This is not surprising, however, since they are more closely related to spiders than real scorpions, and yet of course could not have branched off from spiders before the latter lost any pinchers their ancestors may have had. Since spiders gained their modern traits in the early Devonian, it's entirely possible that pseudoscorpions were actually around long before even the 380 million year old fossil.

This is also supported by the advanced nature of that oldest fossil; it has all of the traits of a modern pseudoscorpion, rather than being some kind of primitive transitional stage on its way to developing the features of this group. This is also not-unusual, as many of the very first land-arthropod fossils show advanced terrestrial features, giving the impression that they had been on land a long time, but simply not preserved as fossils up to that time. Part of this would be a result of geological activity; the suitable land areas have mostly become seabeds, or been subsumed entirely into the mantle by continental drift. Indeed, fossils from the very earliest land animals are extremely rare already, for those very reasons; going back slightly farther, mere chance could result in few or no fossils surviving.

Growth

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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.

Arachnids

Pseudoskorpione | Pseudoscorpionida | Pseudoscorpionida | Drekar | Álskorpiók | Bastaardschorpioenen | カニムシ | Zaleszczotki | Pseudoscorpionida | Лажне скорпије