Spiders
Spiders (Arachnida)
Spiders (pronunciation: /ˈspaɪdər/) 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 diversity among all orders of organisms.
Etymology
The word "spider" derives from the Old English spithra, related to the German Spinne, both of which mean "spinner". This refers to the spider's ability to produce silk and create intricate webs.
Anatomy
Spiders have a two-part body, the front part (cephalothorax) and the abdomen (opisthosoma). Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax.
Behavior
Most spiders are solitary, but some are social and live in communal webs that can house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration to co-operative hunting and food-sharing.
Classification
Spiders are classified in the order Araneae, one of the three orders within the larger group of arachnids. The Araneae order is divided into three sub-orders and about 120 families.
Medical Significance
While all spiders produce venom, only a few species are dangerous to humans. Some spiders, such as the brown recluse and the black widow, have bites that can cause serious medical issues in humans.
Related Terms
- Arachnophobia: An extreme or irrational fear of spiders.
- Arachnology: The scientific study of spiders and related animals such as scorpions, pseudoscorpions, and harvestmen.
- Silk: A natural protein fiber, some forms of which can be woven into textiles. It is produced by several insects, but generally only the silk of moth caterpillars has been used for textile manufacturing.
External links
- Medical encyclopedia article on Spiders
- Wikipedia's article - Spiders
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