Pseudoscorpion
Encyclopedia
A pseudoscorpion, is an arachnid
belonging to the order Pseudoscorpionida, also known as Pseudoscorpiones or Chelonethida.
Pseudoscorpions are generally beneficial to humans since they prey on clothes moth
larvae, carpet beetle
larvae, booklice
, ant
s, mite
s, and small flies
. They are small and inoffensive, and are rarely seen due to their size.
s. They usually range from 2 to 8 mm (0.078740157480315 to 0.31496062992126 ) in length. The largest known species is Garypus titanius of Ascension Island
at up to 12 mm (0.47244094488189 in).
The abdomen, known as the opisthosoma
, is made up of twelve segments, each protected by plates (called tergites above and sternites below) made of chitin
. The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions (the fact that they look exactly like scorpions, aside from not having a stinger tail, is the source of the name "Pseudoscorpion"). 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.
A pseudoscorpion has eight legs with five to seven segments; the number of fused segments is used to distinguish families and genera. They have two very long pedipalp
s with palpal chelae
(pincers) which strongly resemble the pincers found on a scorpion.
The pedipalps generally consist of an immobile "hand" and "finger", with a separate movable finger controlled by an adductor muscle
. A venom gland and duct are usually located in the mobile finger; the poison is used to capture and immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions pour a mildly corrosive fluid over the prey, then ingest the liquefied remains.
Pseudoscorpions spin silk
from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather. However, they do not have book lungs as most of their closest relatives, the spiders, do. They breathe through spiracle
s, a trait they share with the insect
s.
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
, and the young ride on the mother for a short time after they hatch. Up to two dozen young are hatched in a single brood
; there may be more than one brood per year. 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 two to three 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. Some species are arboreal, i.e., live on trees. Some others are phagophiles. Some species are phoretic. They may sometimes be found feeding on mites under the wing covers of certain beetles.
There are more than 3,300 species of pseudoscorpions recorded in more than 430 genera, with more being discovered on a regular basis. They range worldwide, even in temperate to cold regions like Northern Ontario
and above timberline in Wyoming's Rocky Mountains in the United States
and the Jenolan Caves of Australia, but have their most dense and diverse populations in the tropics and subtropics. 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.
Chelifer cancroides is the species most commonly found in homes, where they are often observed in rooms with dusty books. There the tiny animals (2.5–4.5 mm or 0.0984251968503937–0.177165354330709 ) can find their food like booklice and house dust mites. They enter homes by "riding along" with larger insects (known as phoresy
), or are brought in with firewood.
period. It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals.
, who probably found them among scrolls in a library where they would have been feeding on booklice
. Robert Hooke
referred to a "Land-Crab" in his 1665 work Micrographia
. Another reference in the 1780s, when George Adams
wrote of: "A lobster-insect, spied by some labouring men who were drinking their porter, and borne away by an ingenious gentleman, who brought it to my lodging."
Arachnid
Arachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although in some species the front pair may convert to a sensory function. The term is derived from the Greek words , meaning "spider".Almost all extant arachnids are terrestrial...
belonging to the order Pseudoscorpionida, also known as Pseudoscorpiones or Chelonethida.
Pseudoscorpions are generally beneficial to humans since they prey on clothes moth
Moth
A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...
larvae, carpet beetle
Carpet beetle
Carpet beetle may refer to any of the following types of beetle:*Dermestidae, a family of Coleoptera*Varied carpet beetle, a 3 mm–long beetle that can be a serious household pest...
larvae, booklice
Psocoptera
Psocoptera are an order of insects that are commonly known as booklice, barklice or barkflies. They first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the hemipteroids. Their name originates from the Greek word psokos meaning...
, ant
Ant
Ants are social insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from wasp-like ancestors in the mid-Cretaceous period between 110 and 130 million years ago and diversified after the rise of flowering plants. More than...
s, mite
Mite
Mites, along with ticks, are small arthropods belonging to the subclass Acari and the class Arachnida. The scientific discipline devoted to the study of ticks and mites is called acarology.-Diversity and systematics:...
s, and small flies
Diptera
Diptera , or true flies, is the order of insects possessing only a single pair of wings on the mesothorax; the metathorax bears a pair of drumstick like structures called the halteres, the remnants of the hind wings. It is a large order, containing an estimated 240,000 species, although under half...
. They are small and inoffensive, and are rarely seen due to their size.
Characteristics
Pseudoscorpions are small arachnids with a flat, pear-shaped body and pincers that resemble those of scorpionScorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
s. They usually range from 2 to 8 mm (0.078740157480315 to 0.31496062992126 ) in length. The largest known species is Garypus titanius of Ascension Island
Ascension Island
Ascension Island is an isolated volcanic island in the equatorial waters of the South Atlantic Ocean, around from the coast of Africa and from the coast of South America, which is roughly midway between the horn of South America and Africa...
at up to 12 mm (0.47244094488189 in).
Opisthosoma
The opisthosoma is the posterior part of the body in some arthropods, behind the prosoma . It is a distinctive feature of the subphylum Chelicerata...
, is made up of twelve segments, each protected by plates (called tergites above and sternites below) made of chitin
Chitin
Chitin n is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world...
. The abdomen is short and rounded at the rear, rather than extending into a segmented tail and stinger like true scorpions (the fact that they look exactly like scorpions, aside from not having a stinger tail, is the source of the name "Pseudoscorpion"). 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.
A pseudoscorpion has eight legs with five to seven segments; the number of fused segments is used to distinguish families and genera. They have two very long pedipalp
Pedipalp
Pedipalps , are the second pair of appendages of the prosoma in the subphylum Chelicerata. They are traditionally thought to be homologous with mandibles in Crustacea and insects, although more recent studies Pedipalps (commonly shortened to palps or palpi), are the second pair of appendages of the...
s with palpal chelae
Chela (organ)
A chela is a pincer-like organ terminating certain limbs of some arthropods. The name comes from Greek through New Latin . The plural form is chelae. Legs bearing a chela are called chelipeds. Another name is claw because most chelae are curved and have a sharp point like a claw....
(pincers) which strongly resemble the pincers found on a scorpion.
The pedipalps generally consist of an immobile "hand" and "finger", with a separate movable finger controlled by an adductor muscle
Adductor muscle
- Humans :* Adductor muscles of the hip, the most common reference in humans, but may also refer to** Adductor brevis muscle, a muscle in the thigh situated immediately behind the pectineus and adductor longus...
. A venom gland and duct are usually located in the mobile finger; the poison is used to capture and immobilize the pseudoscorpion's prey. During digestion, pseudoscorpions pour a mildly corrosive fluid over the prey, then ingest the liquefied remains.
Pseudoscorpions spin silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
from a gland in their jaws to make disk-shaped cocoons for mating, molting, or waiting out cold weather. However, they do not have book lungs as most of their closest relatives, the spiders, do. They breathe through spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s, a trait they share with the insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s.
Behavior
Some species have an elaborate mating dance, where the male pulls a female over a spermatophoreSpermatophore
A spermatophore or sperm ampulla is a capsule or mass created by males of various animal species, containing spermatozoa and transferred in entirety to the female's ovipore during copulation...
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
Abdomen
In vertebrates such as mammals the abdomen constitutes the part of the body between the thorax and pelvis. The region enclosed by the abdomen is termed the abdominal cavity...
, and the young ride on the mother for a short time after they hatch. Up to two dozen young are hatched in a single brood
Offspring
In biology, offspring is the product of reproduction, of a new organism produced by one or more parents.Collective offspring may be known as a brood or progeny in a more general way...
; there may be more than one brood per year. The young go through three molts
Ecdysis
Ecdysis is the moulting of the cuticula in many invertebrates. This process of moulting is the defining feature of the clade Ecdysozoa, comprising the arthropods, nematodes, velvet worms, horsehair worms, rotifers, tardigrades and Cephalorhyncha...
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 two to three 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. Some species are arboreal, i.e., live on trees. Some others are phagophiles. Some species are phoretic. They may sometimes be found feeding on mites under the wing covers of certain beetles.
Distribution
Northern Ontario
Northern Ontario is a region of the Canadian province of Ontario which lies north of Lake Huron , the French River and Lake Nipissing. The region has a land area of 802,000 km2 and constitutes 87% of the land area of Ontario, although it contains only about 6% of the population...
and above timberline in Wyoming's Rocky Mountains in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and the Jenolan Caves of Australia, but have their most dense and diverse populations in the tropics and subtropics. 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.
Chelifer cancroides is the species most commonly found in homes, where they are often observed in rooms with dusty books. There the tiny animals (2.5–4.5 mm or 0.0984251968503937–0.177165354330709 ) can find their food like booklice and house dust mites. They enter homes by "riding along" with larger insects (known as phoresy
Commensalism
In ecology, commensalism is a class of relationship between two organisms where one organism benefits but the other is neutral...
), or are brought in with firewood.
Evolution
The oldest known fossil pseudoscorpion dates back 380 million years to the DevonianDevonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
period. It has all of the traits of a modern pseudoscorpion, indicating that the order evolved very early in the history of land animals.
Historical references
Pseudoscorpions were first described by AristotleAristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...
, who probably found them among scrolls in a library where they would have been feeding on booklice
Psocoptera
Psocoptera are an order of insects that are commonly known as booklice, barklice or barkflies. They first appeared in the Permian period, 295–248 million years ago. They are often regarded as the most primitive of the hemipteroids. Their name originates from the Greek word psokos meaning...
. Robert Hooke
Robert Hooke
Robert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
referred to a "Land-Crab" in his 1665 work Micrographia
Micrographia
Micrographia is a historic book by Robert Hooke, detailing the then thirty year-old Hooke's observations through various lenses. Published in September 1665, the first major publication of the Royal Society, it was the first scientific best-seller, inspiring a wide public interest in the new...
. Another reference in the 1780s, when George Adams
George Adams (optician)
George Adams Sr was an English optical designer and scientific writer who was also well known as a maker of mathematical instruments and globes. Among his works are a Treatise on the Construction and Use of Globes and an "Essay on the Microscope" .-Biography:His son, George Adams Jr...
wrote of: "A lobster-insect, spied by some labouring men who were drinking their porter, and borne away by an ingenious gentleman, who brought it to my lodging."
Classification
This list follows Joel Hallan's Biology Catalog. Number of Recent genera and species are given in parentheses.- suborder Epiocheirata
- ChthonioideaChthonioideaThe Chthonioidea are a superfamily of pseudoscorpions. The superfamily contains two families:*Tridenchthoniidae — worldwide *Chthoniidae — worldwide...
-
-
- ChthoniidaeChthoniidaeChthoniidae is a family of pseudoscorpions within the superfamily Chthonioidea. The family contains more than 600 species in about 30 genera. Three fossil species are known from Baltic and Dominican amber.-Genera:...
(31, 605) - †Dracochelidae – one fossil species (DevonianDevonianThe Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
) - Lechytiidae (1, 22)
- TridenchthoniidaeTridenchthoniidaeTridenchthoniidae is a family of pseudoscorpions within the superfamily Chthonioidea. The family comprises one fossil and 15 recent genera, containing 70 species:* Anaulacodithella angustimana Beier, 1955 — southern Africa...
(17, 68)- FeaelloideaFeaelloideaThe Feaelloidea are a superfamily of pseudoscorpions with two families, the Feaellidae with a single genus, and the Pseudogarypidae with two.-References:* Joel Hallan's Biology Catalog:...
- Feaelloidea
- FeaellidaeFeaellidaeThe 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...
(1, 12) - PseudogarypidaePseudogarypidaeThe Pseudogarypidae are a small family of pseudoscorpions. Most recent species are found in North America, while one species is endemic to Tasmania.-Species:* Neopseudogarypus J.C.H. Morris, 1948* Neopseudogarypus scutellatus J.C.H...
(2, 7)
- Chthoniidae
-
- suborder Iocheirata
- infraorder Hemictenata
-
-
- NeobisioideaNeobisioideaThe Neobisioidea are a superfamily of pseudoscorpions. The superfamily contains seven families:*Bochicidae*Gymnobisiidae*Hyidae*Ideoroncidae*Neobisiidae*Parahyidae*Syariniidae*Vachoniidae...
-
- BochicidaeBochicidaeBochicidae is a family of pseudoscorpions distributed throughout the Caribbean, Central America and Mexico with one species found as far north as Texas. Members of the family can be diagnosed mainly by features of the claws, notably the presence of exactly 12 trichobothria on each claw and a long,...
(10, 38) - Gymnobisiidae (4, 11)
- Hyidae (3, 9)
- Ideoroncidae (9, 53)
- Neobisiidae (34, 498)
- Parahyidae (1, 1)
- Syarinidae (16, 93)
- infraorder Panctenata
- Bochicidae
- group Elassommatina
-
- CheliferoideaCheliferoideaThe Cheliferoidea are a superfamily of pseudoscorpions. The superfamily contains seven families:*Atemnidae*Miratemnidae*Myrmochernetidae*Chernetidae*Pseudochiriididae*Withiidae*Cheliferidae...
(224, 1261)
-
- Atemnidae (19, 172)
- Cheliferidae (59, 292)
- Chernetidae (112, 643)
- Withiidae (34, 154)
- Sternophoroidea
-
- SternophoridaeSternophoridaeThe 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 , the other two genera are found in the New World, from El Salvador to the southern USA and in the Dominican...
(3, 20)
- Sternophoridae
- Cheliferoidea
- group Mestommatina
-
- GarypoideaGarypoideaThe Garypoidea are a superfamily of pseudoscorpions. The superfamily contains four families:*Garypidae*Olpiidae*Menthidae*Pseudogarypidae...
-
- Cheiridiidae (6, 69)
- Garypidae (10, 74)
- Geogarypidae (3, 61)
- Larcidae (2, 13)
- Pseudochiridiidae (2, 12)
- Olpioidea
-
- MenthidaeMenthidaeThe Menthidae are a small family of pseudoscorpions that are nevertheless spread around the world. While Menthus is found from Mexico to California, Oligomenthus lives in South America. The monotypic genera Paramenthus and Thenmus live in Israel and Australia, respectively.-Species:* Menthus J.C....
(4, 8) - Olpiidae (53, 329)
- Menthidae
- Garypoidea
- Neobisioidea
-
- incertae sedisIncertae sedis, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
- Megathis Stecker, 1875 (nomen dubiumNomen dubiumIn zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
, 2 species)
Further reading
- Mark Harvey. Pseudoscorpions of the World
- Joseph C. Chamberlin (1931): The Arachnid Order Chelonethida. Stanford University Publications in Biological Science. 7(1): 1–284.
- Clarence Clayton Hoff (1958): List of the Pseudoscorpions of North America North of Mexico. American Museum Novitates. 1875. PDF
- Max Beier (1967): Pseudoscorpione vom kontinentalen Südost-Asien. Pacific Insects 9(2): 341–369. PDF
- P. D. Gabbutt (1970): Validity of Life History Analyses of Pseudoscorpions. Journal of Natural History 4: 1–15.
- W. B. Muchmore (1982): Pseudoscorpionida. In "Synopsis and Classification of Living Organisms." Vol. 2. Parker, S.P.
- J. A. Coddington, S. F. Larcher & J. C. Cokendolpher (1990): The Systematic Status of Arachnida, Exclusive of Acari, in North America North of Mexico. In "Systematics of the North American Insects and Arachnids: Status and Needs." National Biological Survey 3. Virginia Agricultural Experiment Station, Virginia Polytechnic Institute and State University.
- Mark S. Harvey (1991): Catalogue of the Pseudoscorpionida. (edited by V . Mahnert). Manchester University Press, Manchester.