Pseudoscorpions are tiny arachnids belonging to the order Pseudoscorpiones (also known as Pseudoscorpionida or Chelonethida). These arthropods are often called ‘false scorpions’ or ‘book scorpions’ because they resemble true scorpions in appearance but lack their elongated tail and characteristic stinger.
Though they appear quite fierce, these arachnids cannot bite and are completely harmless to humans.
These arachnids are usually 2 to 8 mm (0.08 to 0.31 inches) long, with the largest species, Garypus titanius, being as long as 12 mm (0.5 inches).
They have pear-shaped bodies, ranging from yellowish-tan to dark brown in color. The body is divided into two main segments:
This segment bears a pair of sensory pedipalps, eight walking legs (five to seven segments each), and two or four eyes (sometimes no eyes at all). The pedipalps are elongated structures with pincers (palpal chelae) at the end, resembling those of true scorpions. They consist of an immobile ‘hand’ and a mobile’ finger,’ with the latter sometimes bearing venom glands for subduing prey.
The abdomen is typically divided into twelve segments, each protected by hardened plates called tergites (dorsal) and sternites (ventral). Unlike true scorpions, this segment of pseudoscorpions is short and rounded at the rear part, lacking a segmented tail and stinger.
According to the World Pseudoscorpiones Catalog, around 3,300 pseudoscorpion species have been discovered. They are distributed into more than 430 genera, including 24 extant families and 1 extinct family.
Pseudoscorpions are found worldwide, with their highest diversity in the tropics and subtropics, including islands like the Canary and Maltese, where many endemic species are found. However, their range extends to temperate and cold regions, such as Northern Ontario and Wyoming’s Rocky Mountains in the United States.
They primarily inhabit tree barks and tree hollows, leaf and pine litter, moss, and soil. A few species, like Ephippiochthonius borissketi, live in cave environments, such as the Movile Cave in Romania. In coastal areas, pseudoscorpions are found in the intertidal zone, where they inhabit the crevices between rocks.
These arachnids also prefer artificial habitats like damp laundry rooms and basements, whereas the commonly found house pseudoscorpion (Chelifer cancroides) is often sheltered in dusty books.
They primarily inhabit tree barks and tree hollows, leaf and pine litter, moss, and soil. A few species, like Ephippiochthonius borissketi, live in cave environments, such as the Movile Cave in Romania. In coastal areas, pseudoscorpions are found in the intertidal zone, where they inhabit the crevices between rocks.
They also prefer artificial habitats like damp laundry rooms and basements. Chelifer cancroides is the most commonly found pseudoscorpion in houses, often sheltering in dusty books.
Primarily carnivorous, pseudoscorpions feed on various small invertebrates, like dust mites, and insects like ants, flies, springtails, barklice, and booklice. They also actively feed on larvae of cloth mites and skin beetles.
They generally survive around 2 to 3 years in the wild.
The reproductive process of pseudoscorpions involves several behaviors and adaptations. In some species, particularly those in the Cheliferoidea superfamily, the males create a mating territory typically 1 to 2 centimeters in size. They rub their ventral surface on the center of this territory, possibly depositing pheromones to attract females. When a female enters the male’s territory, he initiates a mating dance involving rapid body vibrations and a display of his pedipalps.
The male pseudoscorpion then produces a spermatophore (a packet containing sperm) and navigates the female over it. In some cases, he may also use his forelegs to assist in the insertion of the spermatophore into the female’s genital opening.
The female then picks up the spermatophore deposited by the male. In species with a spermatheca (sperm-storing organ), the female can store the sperm for an extended period before fertilizing her eggs. The eggs are carried in a specialized brood pouch attached to the female’s abdomen.
Multiple broods are possible annually, with around 2 to 50 young hatching from a single brood. These young undergo three molts—protonymph, deutonymph, and tritonymph, with the mother nourishing them using the nutritive milk produced in her ovary. Some species molt in a small, silken, igloo-like structure that protects them from predators during this vulnerable period. Molting stops when these young attain sexual maturity in adulthood.
Their natural predators include birds, like great tits, and arthropods, like spiders and harvestmen.
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