Spider taxonomy
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The Araneae are an order of the arthropod class Arachnida with about 40,000 described species, although there are probably many species that have escaped the human eye to this day, and lots of specimen stored in collections waiting to be described and classified. It is estimated that only one third to one fifth of existing species have been described.
Current arachnid taxonomy divides spiders (Order Araneae) into three 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 literally 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.
See a table of Araneae families at the end of the article with some genera and species listed for each family (only identified species are included).
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[edit] Suborder Mesothelae
These spiders 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)
- Arthromygalidae (primitive spiders)
- Liphistiidae (primitive burrowing spiders)
[edit] Suborder Opisthothelae
This suborder 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 by Mygalomorphs.
[edit] Infraorder Mygalomorphae
Spiders in this infraorder are characterized by the vertical orientation of their chelicerae and the possession of four book lungs.
[edit] Infraorder Araneomorphae
Most, if not all, of the spiders one encounters in everyday life belong to this infraorder. It includes the spiders that weave their beautiful orb webs in the garden, the more chaotic-looking webs of the cobweb spiders the frequent window frames and the corners of rooms, the crab spiders that lurk waiting for nectar- and pollen-gathering insects on flowers, the jumping spiders that patrol outside walls, etc. They are characterized by having chelicerae whole 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.
- Plectreuridae (plectreurid spiders)
- Salticidae (jumping spiders)
The family of Araneae commonly called jumping spiders have a characteristic cephalothorax shapes, as shown in the diagram below. They have eight eyes, two of the 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.
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[edit] Table of Families
Families listed in boldface contain one or more species which are known to be dangerous to humans.
| 1 | <10 | >=10 | >=100 | >=1000 |
- Sources:
- The World Spider Catalog, Version 7.0 (families, species count)
- Synopsis of the described Araneae of the World (suborders)
[edit] See also
[edit] References
- Reiskind, J. (1965). The Taxonomic Problem of Sexual Dimorphism in Spiders and a Synonymy in Myrmecotypus (Araneae, Clubionidae). Psyche 72:279-281 PDF (Creative Commons Attribution 2.5 license)
