Pseudoscorpiones

de Geer, 1778

pseudoscorpions, false scorpions, book scorpions

Suborder Guides

Pseudoscorpions are tiny arachnids, most under 5 mm in length, superficially resembling scorpions but lacking a stinger and elongated tail. They are among the oldest terrestrial colonizers, with fossils dating to the Middle Devonian (ca. 390 million years ago). Despite their ancient lineage, they exhibit remarkable morphological stasis, with even Devonian fossils appearing modern. Most inhabit concealed microhabitats such as beneath bark, in leaf litter, soil, caves, or mammal nests, making them seldom encountered despite being fairly common. They are predatory, seizing small prey with venomous pincer-like .

Garypidae by (c) Casey H. Richart, some rights reserved (CC BY), uploaded by Casey H. Richart. Used under a CC-BY license.

Chthonius tetrachelatus by (c) davidfdz_b82, some rights reserved (CC BY), uploaded by davidfdz_b82. Used under a CC-BY license.

Chthonius tetrachelatus by (c) Evrytte Carlson, some rights reserved (CC BY), uploaded by Evrytte Carlson. Used under a CC-BY license.

Pronunciation

How to pronounce Pseudoscorpiones: /ˌsjuːdoʊˌskɔːrpiˈoʊniːz/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from true scorpions (order Scorpiones) by the complete absence of a tail and stinger. Separated from other small arachnids by the prominent, muscular pincer-like with venom glands. The combination of eight legs, two body segments ( and ), and large appendages resembling claws is diagnostic. Many require microscopic examination for definitive identification.

Images

Habitat

Inhabits concealed microhabitats including spaces beneath bark on trees, stumps, and logs; leaf litter; topsoil; mammal nests; caves; and human dwellings. Found in virtually all habitable continental environments from tropical to temperate regions, including both wet and dry conditions. Some are cave-adapted troglobites.

Distribution

Global distribution with records from all continents except Antarctica. In Canada, 25 are known with transcontinental range from British Columbia to the Maritimes and Newfoundland, extending north to 67°N in Yukon. Malaysia records 41 species. New species continue to be discovered regularly, including recent descriptions from Colombia, French Polynesia, and Colorado caves.

Diet

. Prey includes small such as springtails, barklice, fly larvae, and mites. Prey is captured with venomous chelae, then passed to for puncturing or crushing, followed by extraoral digestion with regurgitated before ingestion.

Host Associations

Cerambycidae (longhorned beetles) - Pseudoscorpions attach to beetles for to new dead wood . Observed on Stenosphenus notatus and other wood-boring .
Diptera (flies) - Most frequently reported insect order for pseudoscorpion ; includes crane flies and other associated with decaying wood.
Braconid wasps - of wood-boring beetles serve as phoretic .

Life Cycle

Development includes , post-embryonic nymphal stages, and . Females spin silk egg sacs using glands in the . Silk is also used to construct molting chambers and retreats. Some take multiple seasons to complete development; details vary considerably among species.

Behavior

is the primary mechanism: pseudoscorpions attach to the outer surface of insects or other animals, ceasing feeding and development during transport. Some exhibit social , living side by side with conspecifics and using rhythmic body or movements to communicate. Courtship involves complex including deposition, with males of some species constructing elaborate silken bowers to guide females. In the most derived species, males grasp female pedipalps and guide them over spermatophores in a 'dancing' behavior.

Ecological Role

of microinvertebrates in concealed ; contribute to decomposition processes in dead wood and soil . Their phoretic relationships with wood-boring insects may facilitate of ephemeral resources such as newly dead trees.

Human Relevance

Occasionally found in homes (hence 'book ' ) where they prey on small pests such as booklice and mites; entirely harmless to humans despite venom glands. New discoveries highlight unexplored biodiversity in caves and previously inaccessible regions. Serve as indicators for conservation of microhabitats and cave .

Similar Taxa

Scorpiones (true scorpions)True scorpions possess an elongated metasoma (tail) with terminal stinger; pseudoscorpions completely lack this structure.
Acari (mites and ticks)Mites and ticks are generally smaller with less prominent appendages and often have body regions lacking the distinct chelae of pseudoscorpions.

More Details

Fossil Record

Pseudoscorpions have one of the oldest fossil records among terrestrial arachnids, with specimens from the Middle Devonian (ca. 390 Ma). Most fossil records from the Mesozoic and Cenozoic are amber inclusions, primarily from Baltic, Burmese, and Dominican ambers. Sixteen of 26 extant have fossil representatives. A major gap of nearly 250 million years exists between Palaeozoic and Mesozoic records. The group exhibits remarkable morphological stasis, with fossil forms closely resembling modern .

Phoresy Debates

While is widely accepted as the primary mechanism, alternative hypotheses have been proposed including accidental boarding, obligate , and phagophily (preying on other associates). At least one study on Cordylochernes scorpioides on harlequin beetles supports the dispersal hypothesis, with large males defending beetle as strategic sites for mating.