Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like

arachnid Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroon ...

s belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. Pseudoscorpions are generally beneficial to humans since they prey on

clothes moth Clothes moth or clothing moth is the common name for several species of moth considered to be pests, whose larvae eat animal fibres (hairs), including clothing and other fabrics. These include: * ''Tineola bisselliella'', the common clothes moth ...

larvae, carpet beetle larvae,

booklice Psocoptera are a paraphyletic group of insects that are commonly known as booklice, barklice or barkflies. The name Psocoptera has been replaced with Psocodea in recent literature, with the inclusion of the former order Phthiraptera into Psocod ...

ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...

mite Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...

s, and small

flies Flies are insects of the order Diptera, the name being derived from the Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwings having evolved into advanced ...

. They are tiny, and are rarely noticed due to their small size, despite being common in many environments. When people do see pseudoscorpions, especially indoors, they are often mistaken for

tick Ticks (order Ixodida) are parasitic arachnids that are part of the mite superorder Parasitiformes. Adult ticks are approximately 3 to 5 mm in length depending on age, sex, species, and "fullness". Ticks are external parasites, living by ...

s or small

spider Spiders ( order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

s. Pseudoscorpions often carry out

phoresis Phoresis or phoresy is a non-permanent, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) solely for the purpose of travel. Phoresis has been observed directly in ticks and mites s ...

, a form of

commensalism Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...

in which one organism uses another for the purpose of transport.

Characteristics

Pseudoscorpions belong to the class

Arachnida Arachnida () is a class of joint-legged invertebrate animals (arthropods), in the subphylum Chelicerata. Arachnida includes, among others, spiders, scorpions, ticks, mites, pseudoscorpions, harvestmen, camel spiders, whip spiders and vinegaroon ...

. They are small arachnids with a flat, pear-shaped body, and pincer-like

pedipalp Pedipalps (commonly shortened to palps or palpi) are the second pair of appendages of chelicerates – a group of arthropods including spiders, scorpions, horseshoe crabs, and sea spiders. The pedipalps are lateral to the chelicerae ("jaws") and ...

s that resemble those of

scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always end ...

s. They usually range from in length.

Pennsylvania State University The Pennsylvania State University (Penn State or PSU) is a Public university, public Commonwealth System of Higher Education, state-related Land-grant university, land-grant research university with campuses and facilities throughout Pennsylvan ...

, Department
Entomological Notes: Pseudoscorpion Fact Sheet
/ref> The largest known species is ''

Garypus titanius ''Garypus titanius'', the giant pseudoscorpion, is the largest species of pseudoscorpion—small, scorpion-looking creatures—in the world. Critically endangered, it is restricted to Boatswain Bird Island, a small rocky island off Ascension Isla ...

'' of

Ascension Island Ascension Island is an isolated volcanic island, 7°56′ south of the Equator in the South Atlantic Ocean. It is about from the coast of Africa and from the coast of South America. It is governed as part of the British Overseas Territory o ...

at up to . Range is generally smaller at an average of . A pseudoscorpion has eight legs with five to seven segments each; the number of fused segments is used to distinguish families and genera. They have two very long

s with palpal

chelae A chela ()also called a claw, nipper, or pinceris a pincer (biology), pincer-like organ at the end of certain limbs of some arthropods. The name comes from Ancient Greek , through New Latin '. The plural form is chelae. Legs bearing a chela are ...

(pincers), which strongly resemble the pincers found on a scorpion. The pedipalps generally consist of an immobile "hand" and mobile "finger", the latter controlled by an adductor muscle. Members of the clade Iocheirata, which contains the majority of pseudoscorpions, are

venom Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...

ous, with a venom gland and duct usually located in the mobile finger; the venom is used to immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions exude a mildly corrosive fluid over the prey, then ingest the liquefied remains. Kaldari pseudoscorpion 01

The abdomen, referred to as the

opisthosoma The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma (cephalothorax). It is a distinctive feature of the subphylum Chelicerata (arachnids, horseshoe crabs and others). Although it is similar in most respects to a ...

, is made up of twelve segments, each protected by sclerotized plates (called

tergite A ''tergum'' (Latin for "the back"; plural ''terga'', associated adjective tergal) is the dorsal ('upper') portion of an arthropod segment other than the head. The anterior edge is called the 'base' and posterior edge is called the 'apex' or 'mar ...

s above and

sternite The sternum (pl. "sterna") is the ventral portion of a segment of an arthropod thorax or abdomen. In insects, the sterna are usually single, large sclerites, and external. However, they can sometimes be divided in two or more, in which case the ...

s below). The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions. The color of the body can be yellowish-tan to dark-brown, with the paired claws often a contrasting color. They may have two, four or no eyes. Pseudoscorpions spin

silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the coc ...

from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather, but they do not have

book lungs A book lung is a type of respiration organ used for atmospheric gas exchange that is present in many arachnids, such as scorpions and spiders. Each of these organs is located inside an open ventral abdominal, air-filled cavity (atrium) and conn ...

like true scorpions and the

Tetrapulmonata Tetrapulmonata is a non-ranked supra-ordinal clade of arachnids. It is composed of the extant orders Thelyphonida (whip scorpions), Schizomida (short-tailed whip scorpions), Amblypygi (tail-less whip scorpions) and Araneae (spiders). It is the ...

. Instead, they breathe exclusively through

trachea The trachea, also known as the windpipe, is a Cartilage, cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air-breathing animals with lungs. The trachea extends ...

e, which open laterally through two pairs of spiracles on the posterior margins of the sternites of abdominal segments 3 and 4.

Behavior

Some species have an elaborate mating dance, where the male pulls a female over a

spermatophore A spermatophore or sperm ampulla is a capsule or mass containing spermatozoa created by males of various animal species, especially salamanders and arthropods, and transferred in entirety to the female's ovipore during reproduction. Spermatophores ...

previously laid upon a surface. In other species, the male also pushes the sperm into the female genitals using the forelegs. The female carries the fertilized eggs in a brood pouch attached to her

abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...

, and the young ride on the mother for a short time after they hatch. Between 20 and 40 young are hatched in a single

brood Brood may refer to: Nature * Brood, a collective term for offspring * Brooding, the incubation of bird eggs by their parents * Bee brood, the young of a beehive * Individual broods of North American Periodical Cicadas: ** Brood X, the largest bro ...

, with more than one brood per year possible. The young go through three molts over the course of several years before reaching adulthood. Many species molt in a small, silken igloo that protects them from enemies during this vulnerable period. After reaching adulthood, pseudoscorpions live 2–3 years. They are active in the warm months of the year, overwintering in silken cocoons when the weather grows cold. Smaller species live in debris and

humus In classical soil science, humus is the dark organic matter in soil that is formed by the decomposition of plant and animal matter. It is a kind of soil organic matter. It is rich in nutrients and retains moisture in the soil. Humus is the Lati ...

. Some species are

arboreal Arboreal locomotion is the Animal locomotion, locomotion of animals in trees. In habitats in which trees are present, animals have evolved to move in them. Some animals may scale trees only occasionally, but others are exclusively arboreal. Th ...

, while others are

phagophile Phagophilia or phagophily is feeding on parasites. German zoologist M. Beier reported that phagophilia is the feeding behavior of some pseudoscorpions. It was reported that many pseudoscorpions species co-exist with some packrat species, and two o ...

s, eating parasites in an example of

cleaning symbiosis Cleaning symbiosis is a mutually beneficial association between individuals of two species, where one (the cleaner) removes and eats parasites and other materials from the surface of the other (the client). Cleaning symbiosis is well-known amon ...

. Some species are

phoretic Phoresis or phoresy is a non-permanent, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) solely for the purpose of travel. Phoresis has been observed directly in ticks and mites s ...

, others may sometimes be found feeding on mites under the wing covers of certain beetles.

Distribution

More than 3,300 species of pseudoscorpions are recorded in more than 430 genera, with more being discovered on a regular basis. They range worldwide, even in temperate to cold regions such as

Northern Ontario Northern Ontario is a primary geographic and quasi-administrative region of the Canadian province of Ontario, the other primary region being Southern Ontario. Most of the core geographic region is located on part of the Superior Geological Provi ...

and above the timberline in Wyoming's Rocky Mountains in the United States and the

Jenolan Caves The Jenolan Caves (Tharawal language, Tharawal: ''Binoomea'', ''Bindo'', ''Binda'') are limestone cave, limestone caves located within the Jenolan Karst Conservation Reserve in the Central Tablelands region, west of the Blue Mountains (New South ...

of Australia, but have their most dense and diverse populations in the

tropics The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...

and subtropics, where they spread even to island territories such as the

Canary Islands The Canary Islands (; es, Canarias, ), also known informally as the Canaries, are a Spanish autonomous community and archipelago in the Atlantic Ocean, in Macaronesia. At their closest point to the African mainland, they are west of Morocc ...

, where around 25

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...

species have been found. There are also two endemic species on the

Maltese Islands Malta ( , , ), officially the Republic of Malta ( mt, Repubblika ta' Malta ), is an island country in the Mediterranean Sea. It consists of an archipelago, between Italy and Libya, and is often considered a part of Southern Europe. It lies ...

. Species have been found under tree bark, in leaf and pine litter, in soil, in tree hollows, under stones, in caves such as the

Movile Cave Movile Cave () is a cave near Mangalia, Constanța County, Romania discovered in 1986 by Cristian Lascu a few kilometers from the Black Sea coast. It is notable for its unique groundwater ecosystem abundant in hydrogen sulfide and carbon dioxi ...

, at the seashore in the intertidal zone, and within fractured rocks. '' Chelifer cancroides'' is the species most commonly found in homes, where it is often observed in rooms with dusty books. There, the tiny animals () can find their food such as booklice and

house dust mites House dust mites (HDM, or simply dust mites) are various species of acariform mites belonging to the family Pyroglyphidae that are found in association with dust in dwellings. They are known for causing allergies. Biology Species The current ...

. They enter homes by riding insects (

phoresy Phoresis or phoresy is a non-permanent, Commensalism, commensalistic interaction in which one organism (a phoront or phoretic) attaches itself to another (the host) solely for the purpose of travel. Phoresis has been observed directly in Acari ...

) larger than themselves, or are brought in with firewood.

Evolution

The oldest known fossil pseudoscorpion, '' Dracochela deprehendor'' is known from

cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...

fragments of nymphs found in the

Panther Mountain Formation The Panther Mountain Formation is a geologic formation in New York. It preserves fossils dating back to the Devonian period. It is located in the counties of Albany, Madison, Oneida, Otsego, and Schoharie. It is well known for its fossil ...

near Gilboa in

New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...

, dating to the mid-

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

, around 383 million years ago. It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals. Its morphology suggests that it is more primitive than any living pseudoscorpion. As with most other arachnid orders, the pseudoscorpions have changed very little since they first appeared, retaining almost all the features of their original form. After the Devonian fossils, almost no other fossils of pseudoscorpions are known for over 250 million years until

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

fossils in

amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In Ma ...

, all belonging to modern families, suggesting that the major diversification of pseudoscorpions had already taken place by this time. The only fossil from this time gap is '' Archaeofeaella'' from the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

of Ukraine, approximately 227 million years ago, which is suggested to be an early relative of the family

Feaellidae The Feaellidae are a family of pseudoscorpions with the single genus ''Feaella''. Species Feaella Ellingsen, 1906 * subgenus ''Feaella'' Ellingsen, 1906 ** '' Feaella mirabilis'' Ellingsen, 1906 — western Africa ** '' Feaella mombasica'' Beie ...

Historical references

Pseudoscorpions were first described by

Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...

, who probably found them among scrolls in a library where they would have been feeding on

Robert Hooke Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...

referred to a "Land-Crab" in his 1665 work ''

Micrographia ''Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon.'' is a historically significant book by Robert Hooke about his observations through various lenses. It w ...

''. Another reference in the 1780s, when George Adams wrote of "a lobster-insect, spied by some labouring men who were drinking their

porter Porter may refer to: Companies * Porter Airlines, Canadian regional airline based in Toronto * Porter Chemical Company, a defunct U.S. toy manufacturer of chemistry sets * Porter Motor Company, defunct U.S. car manufacturer * H.K. Porter, Inc., ...

, and borne away by an ingenious gentleman, who brought it to my lodging."

Classification

The following taxon numbers are calculated as of the end of 2012. * Order Pseudoscorpiones De Geer, 1778 (2 suborders) :::* † Family Dracochelidae Schawaller, Shear and Bonamo, 1991 (1 fossil genus, 1 fossil species) ::* Superfamily

Chthonioidea The Chthonioidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. ...

Daday, 1888 (2 families) :::* Family Chthoniidae Daday, 1888 (44 genera, 700+ species fossil species :::* Family Pseudotyrannochthoniidae Beier, 1932 (5 genera, 49 species) ::* Superfamily

Feaelloidea The Feaelloidea are a superfamily of pseudoscorpions with two families, the Feaellidae The Feaellidae are a family of pseudoscorpions with the single genus ''Feaella''. Species Feaella Ellingsen, 1906 * subgenus ''Feaella'' Ellingsen, 1906 ** ...

Ellingsen, 1906 (2 families) :::* Family

Ellingsen, 1906 (1 genus, 12 species) :::* Family Pseudogarypidae Chamberlin, 1923 (2 genera, 7 species fossil species :* Suborder Iocheirata Harvey, 1992 (5 superfamilies) ::* Superfamily

Neobisioidea The Neobisioidea are a superfamily of pseudoscorpions. The superfamily contains seven families: * Bochicidae * Gymnobisiidae * Hyidae * Ideoroncidae *Neobisiidae Neobisiidae is a family of pseudoscorpions distributed throughout Africa, the ...

Chamberlin, 1930 (7 families) :::* Family Bochicidae Chamberlin, 1930 (12 genera, 42 species) :::* Family Gymnobisiidae Beier, 1947 (4 genera, 11 species) :::* Family Hyidae Chamberlin, 1930 (2 genera, 14 species) :::* Family Ideoroncidae Chamberlin, 1930 (11 genera, 59 species) :::* Family

Neobisiidae Neobisiidae is a family of pseudoscorpions distributed throughout Africa, the Americas and Eurasia and consist of 550 species in 32 genera. Some species live in caves while some are surface-dwelling. Characteristics The body color ranges from re ...

Chamberlin, 1930 (33 genera, 595 species fossil species :::* Family Parahyidae Harvey, 1992 (1 genus, 1 species) :::* Family Syarinidae Chamberlin, 1930 (18 genera, 111 species) ::* Superfamily

Garypoidea The Garypoidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida. ...

Simon, 1879 (6 families) :::* Family Garypidae Simon, 1879 (10 genera, 80 species) :::* Family Garypinidae Daday, 1888 (21 genera, 76 species fossil species :::* Family Geogarypidae Chamberlin, 1930 (3 genera, 60 species fossil species :::* Family Larcidae Harvey, 1992 (2 genera, 15 species) :::* Family Menthidae Chamberlin, 1930 (5 genera, 12 species) :::* Family Olpiidae Banks, 1895 (36 genera, 268 species) ::* Superfamily

Cheiridioidea The Cheiridioidea are a superfamily of pseudoscorpion Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudoscorpionida or Chelonethida ...

Hansen, 1894 (2 families) :::* Family Cheiridiidae Hansen, 1894 (7 genera, 73 species fossil genus, 3 fossil species :::* Family Pseudochiridiidae Chamberlin, 1923 (2 genera, 12 species fossil species ::* Superfamily

Sternophoroidea The Sternophoridae are a family of pseudoscorpions with about 20 described species in three genera. While ''Afrosternophorus'' is an Old World genus, found mainly in Australasia (with, despite its name, only one African species), the other two ge ...

Chamberlin, 1923 (1 family) :::* Family Sternophoridae Chamberlin, 1923 (3 genera, 20 species) ::* Superfamily

Cheliferoidea The Cheliferoidea are a superfamily of pseudoscorpions. Families The superfamily contains the following families: * Atemnidae Kishida, 1929 (Chamberlin, 1931?) * Miratemnidae (Sometimes considered a subfamily of Atemnidae, Miratemninae) * Myrmo ...

Risso, 1827 (4 families) :::* Family Atemnidae Kishida, 1929 (21 genera, 178 species fossil genus, 1 fossil species :::* Family Cheliferidae Risso, 1827 (58 genera, 273 species fossil genus, 12 fossil species :::* Family

Chernetidae The Chernetidae are a family of pseudoscorpions with over 650 described species and 110 genera. Subfamilies Subfamilies and genera include: ;Chernetinae Chernetinae is a subfamily of pseudoscorpions in the family Chernetidae. Genera - '' A ...

Menge, 1855 (117 genera, 663 species fossil genus, 3 fossil species :::* Family

Withiidae Withiidae is a family of pseudoscorpions belonging to the order Pseudoscorpiones Pseudoscorpions, also known as false scorpions or book scorpions, are small, scorpion-like arachnids belonging to the order Pseudoscorpiones, also known as Pseudos ...

Chamberlin, 1931 (36 genera, 158 species fossil genus, 1 fossil species

Cladogram

After Benavides et al, 2019, with historic taxonomic groups from Harvey (1992).

References

External links

* *
Video of Pseudoscorpions in Ireland
{{Authority control Extant Devonian first appearances