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Spider taxonomy is the alpha taxonomy of the spiders, members of the Araneae order of the arthropod class Arachnida with about 40,000 described species. However there are likely many species that have escaped the human eye to this day, and many specimens stored in collections waiting to be described and classified. It is estimated that only one half to one third of total existing species have been described. 
Arachnologists currently divide spiders into two suborders with about 38 superfamilies, and 111 families. Seven of the 111 families are incertae sedis, meaning that their placement into superfamilies is not agreed upon; several other families are not placed in any superfamily.
Due to constant research, with new species being discovered every month and others being recognized as synonyms, the number of species in the families is bound to change and can never reflect the present status with total accuracy. Nevertheless, the species numbers given here are useful as a guideline.
Spider taxonomy can be traced to the work of Swedish naturalist Carl Alexander Clerck, who in 1757 published the first binomial scientific names of some 67 spiders species in his Svenska Spindlar ("Swedish Spiders"), one year before Linnaeus named over 30 spiders in his Systema Naturae. In the ensuing 250 years, thousands more species have been described by researchers around the world, yet only dozen taxonomists are responsible for more than a third of all species described. The most prolific authors include Eugène Simon of France, Norman Platnick, Herbert Walter Levi of the United States, Embrik Strand of Norway, and Tamerlan Thorell of Sweden, each of whom having described well over 1,000 species.
Mesothelae resemble the Solifugae ("wind scorpions" or "sun scorpions") in having segmented plates on their abdomens that create the appearance of the segmented abdomens of these other arachnids. They are both few in number and also limited in geographical range.
- Arthrolycosidae (primitive spiders, extinct)
- Arthromygalidae (primitive spiders, extinct)
- Liphistiidae (primitive burrowing spiders)
Suborder Opisthothelae contains the spiders that have no plates on their abdomens. It can be somewhat difficult on casual inspection to determine whether the chelicerae of members are of the sort that would put them into the infraorder of the mygalomorphs or the infraorder of the Araneomorphs. The spiders that are called "tarantulas" in English are so large and hairy that inspection of their chelicerae is hardly necessary to categorize one of them as a Mygalomorph. Other, smaller, members of this suborder, however, look little different from the Araneomorphs. (See the picture of the Sphodros rufipes below.) Many Araneomorphs are immediately identifiable as such since they are found on webs designed for the capture of prey or exhibit other habitat choices that eliminate the possibility that they could be Mygalomorphs.
Spiders in infraorder Mygalomorphae are characterized by the vertical orientation of their chelicerae and the possession of four book lungs.
Most, if not all, of the spiders one is likely to encounter in everyday life belong to infraorder Araneomorphae. It includes a wide range from the spiders that weave their distinctive orb webs in the garden, the more chaotic-looking webs of the cobweb spiders that frequent window frames and the corners of rooms, the crab spiders that lurk waiting for nectar- and pollen-gathering insects on flowers, to the jumping spiders that patrol the outside walls of a dwelling, and so on. They are characterized by having chelicerae whose tips approach each other as they bite, and (usually) having one pair of book lungs.
Some important spider families are :
- Pholcidae (daddy long-legs spiders)
These spiders are frequently seen in cellars. When light contact disturbs their web their characteristic response is to set the entire web moving the way a person would jump up and down on a trampoline. It is unclear why they cause their webs to vibrate in this way; moving their webs back and forward may increase the possibility that insects flying close by may be ensnared, or the rapid gyrations caused by the spider in its web may make the spider harder to target by predators.
- Plectreuridae (plectreurid spiders)
- Salticidae (jumping spiders)
The family of Salticidae commonly called jumping spiders have a characteristic cephalothorax shapes, as shown in the diagram below. They have eight eyes, two of them very prominent, and excellent vision. Their maximum size is perhaps 13/16 inch (20 mm), but many species are much smaller than that. The largest North American species such as Phidippus regius, P. octopunctatis, etc., are so heavy bodied that they cannot jump far. The smaller species of jumping spider can jump many times their own body length. They hunt by first getting within range of a prey animal such as a fly, securing a silken "climbing rope" to their current perch, and then jumping onto their prey and biting it. Many seem to take unerring aim at the neck of their prey. Should they jump from one twig to another in an attempt to capture prey and miss or get knocked off the second twig by their struggling prey then they are protected from falling by their silken lifeline. At night these spiders usually retreat to a silken "puptent" that they construct for their own protection and, when needed, as a place to deposit their eggs. They are frequently seen in sunlit areas on walls, tree trunks, and other such vertical surfaces. They are perhaps the only family of spiders who will take cognizance of a human in their general area and then turn their bodies and elevate their cephalothoraxes to keep the human under observation. If approached closely, e.g., with the lens of a camera, some of them may choose to jump onto the nearby object to explore it. This behavior may be alarming but it never seems to be aggressive since these spiders are unwilling to attack prey that are very much larger than they are.
Table of Families
Families listed in boldface contain one or more species which are believed to be venomous to humans.
- Abbreviations for Insect and Spider Collections of the World
- International Commission on Zoological Nomenclature
- European and Australian spiders - info and identification
- Spiders of Europe and Greenland
- Information about the largest spider