Temporal range: Palaeogene–present
|175 genera, 2,155 species|
The Thomisidae are a family of spiders, including about 175 genera and over 2,100 species. The common name crab spider is often linked to species in this family, but is also applied loosely to many other families of spiders. Many members of this family are also known as flower spiders or flower crab spiders.
Family is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy; it is classified between order and genus. A family may be divided into subfamilies, which are intermediate ranks between the ranks of family and genus. The official family names are Latin in origin; however, popular names are often used: for example, walnut trees and hickory trees belong to the family Juglandaceae, but that family is commonly referred to as being the "walnut family".
Spiders are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of July 2019, at least 48,200 spider species, and 120 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
A genus is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.
Spiders in this family are called "crab spiders" due to their resemblance to crabs, the way such spiders hold their two front pairs of legs, and their ability to scuttle sideways or backwards.The Thomisidae are the family most generally referred to as "crab spiders", though some members of the Sparassidae are called "giant crab spiders", the Selenopidae are called "wall crab spiders", and various members of the Sicariidae are sometimes called "six-eyed crab spiders". Some unrelated orb-weaver spider species such as Gasteracantha cancriformis also are commonly called "crab spiders".
Huntsman spiders, members of the family Sparassidae, are known by this name because of their speed and mode of hunting. They also are called giant crab spiders because of their size and appearance. Larger species sometimes are referred to as wood spiders, because of their preference for woody places. In southern Africa the genus Palystes are known as rain spiders or lizard-eating spiders. Commonly they are confused with baboon spiders from the Mygalomorphae infraorder, which are not closely related.
Sicariidae is a family of six-eyed venomous spiders known for their potentially necrotic bites. The family consists of three genera and about 160 species. Well known spiders in this family include the brown recluse spider and the six-eyed sand spider.
Orb-weaver spiders or araneids are members of the spider family Araneidae. They are the most common group of builders of spiral wheel-shaped webs often found in gardens, fields and forests. "Orb" can in English mean "circular", hence the English name of the group. Araneids have eight similar eyes, hairy or spiny legs, and no stridulating organs.
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Thomisidae do not build webs to trap prey, though all of them produce silk for drop lines and sundry reproductive purposes; some are wandering hunters and the most widely known are ambush predators. Some species sit on or beside flowers or fruit, where they grab visiting insects. Individuals of some species, such as Misumena vatia , are able to change color over a period of some days, to match the flower on which they are sitting. Some species frequent promising positions among leaves or bark, where they await prey, and some of them sit in the open, where they are startlingly good mimics of bird droppings. However, these members of the family Thomisidae are not to be confused with the spiders that generally are called bird-dropping spiders, not all of which are close relatives of crab spiders.
Spider silk is a protein fibre spun by spiders. Spiders use their silk to make webs or other structures, which function as sticky nets to catch other animals, or as nests or cocoons to protect their offspring, or to wrap up prey. They can also use their silk to suspend themselves, to float through the air, or to glide away from predators. Most spiders vary the thickness and stickiness of their silk for different uses.
Ambush predators or sit-and-wait predators are carnivorous animals that capture or trap prey by stealth or by strategy, rather than by speed or by strength. Ambush predators sit and wait for prey, often from a concealed position, and then launch a rapid surprise attack.
Misumena vatia is a species of crab spider with holarctic distribution. In North America, where it is the largest and best-known flower spider, it is called the goldenrod crab spider or flower (crab) spider, because it is commonly found hunting in goldenrod sprays in the autumn. Young males in the early summer may be quite small and easily overlooked, but females can grow up to 10 mm (0.39 in) ; males reach 5 mm (0.20 in) at most.
Other species of crab spiders with flattened bodies either hunt in the crevices of tree trunks or under loose bark, or shelter under such crevices by day, and come out at night to hunt. Members of the genus Xysticus hunt in the leaf litter on the ground. In each case, crab spiders use their powerful front legs to grab and hold on to prey while paralysing it with a venomous bite.
Xysticus is a genus of ground crab spiders described by C. L. Koch in 1835, belonging to the order Araneae, family Thomisidae. The genus name is derived from the Ancient Greek root xyst, meaning "scraped, scraper".
The spider family Aphantochilidae was incorporated into the Thomisidae in the late 1980s. Aphantochilus species mimic Cephalotes ants, on which they prey.
Aphantochilus is a small genus of ant-mimicking crab spiders from Central and South America.
Cephalotes is a Neotropical genus of tree-dwelling ant species, commonly known as turtle ants. All appear to be gliding ants, with the ability to "parachute" and steer their fall so as to land back on the tree trunk rather than fall to the ground, which is often flooded.
The spiders of Thomisidae are not known to be harmful to humans. However, spiders of an unrelated genus, Sicarius , which are sometimes referred to as "crab spiders", or "six-eyed crab spiders", are close cousins to the recluse spiders, and are highly venomous, though human bites are rare.
The recluse spiders, also known as brown spiders, fiddle-backs, violin spiders, and reapers, is a genus of spiders that was first described by R. T. Lowe in 1832. They are venomous spiders known for their bite, which sometimes produces a characteristic set of symptoms known as loxoscelism.
A spider bite, also known as arachnidism, is an injury resulting from the bite of a spider. The effects of most bites are not serious. Most bites result in mild symptoms around the area of the bite. Rarely they may produce a necrotic skin wound or severe pain.
Several different types of sexual dimorphism have been recorded in crab spiders. Some species exhibit color dimorphisms;however, the most apparent dimorphism is the difference in size between males and females. In some species, this is relatively small; females of Misumena vatia are roughly twice the size of their male counterparts. In other cases, the difference is extreme; on average, female Thomisus onustus and Misumena vatia are more than 60 times as massive as the males.
Several hypothesized explanations are given for the evolution of sexual size dimorphisms in the Thomisidae and other sister taxa.The most widely acknowledged hypothesis for female growth is the fecundity hypothesis: selection favors larger females so they can produce more eggs and healthier offspring. Because males do not carry and lay eggs, a growth in size does not confer a fitness advantage.
However, sexual size dimorphism may be a result of male dwarfism. The gravity hypothesis states that the smaller size allows the male to travel with greater ease, providing him with an increased opportunity to find mates.Females are comparatively stationary and a smaller size provides them no additional benefit.
Other hypotheses propose that sexual size dimorphism evolved by chance, and no selective advantage exists to larger females or smaller males.
As of October 2015 [update] , this large family contains around 170 genera:
Philodromidae, also known as philodromid crab spiders and running crab spiders, is a family of araneomorph spiders first described by Tord Tamerlan Teodor Thorell in 1870. It contains over 600 species in thirty genera. Most are dull colored- brown, gray, yellowish or mottled with a leaf-like cardiac mark on the anterior dorsal abdomen, and seldom reach above 10 millimetres (0.39 in) long. None of the species build webs, but they do use silk for draglines and egg sacs.
Misumenops is a common genus of crab spider with more than 50 described species.
Misumenoides is a genus of spiders in the family Thomisidae. Spiders in this family are commonly called "crab" or "flower" spiders.
Hogna is a genus of wolf spiders with more than 200 described species. It is found on all continents except Antarctica.
Tmarus is a genus of crab spiders, comprising the following species:
Tetragnatha is a genus of spiders containing hundreds of species. They are found all over the world, although most occur in the tropics and subtropics. They are commonly called stretch spiders, referring to their elongated body form. When disturbed they will stretch their front legs forward and the others in the other direction, thus being able to hide on blades of grass or similar elongated substrates. They are able to run over water.
Thomisus is a genus of crab spiders with almost 150 species described. The genus includes species that vary widely in their ecology, but the best known crab spiders are those species that people call the flower crab spiders, because they are ambush predators that feed on insects visiting flowers. The flower crab spiders are the species for which the popular name was coined, because of their crab-like motion and their way of holding their front legs in an attitude reminiscent of a crab spreading its claws as a threat.
Trochosa is a large wolf spider genus found worldwide.
Synema is a genus of spider in the family Thomisidae, found in most parts of the world.
Stephanopis is a genus of crab spiders first described by Octavius Pickard-Cambridge in 1869.