Spiders

Spiders are predatory invertebrate animals with two body segments, eight legs, no chewing mouth parts and no wings. They are classified in the order Araneae, one of several orders within the larger class of arachnids, a group which also contains scorpions, whip scorpions, mites, ticks, and Opiliones (harvestmen). The study of spiders is known as arachnology.

All spiders produce silk, a thin, strong protein strand extruded by the spider from spinnerets most commonly found on the end of the abdomen. Many species use it to trap insects in webs, although there are many species that hunt freely. Silk can be used to aid in climbing, form smooth walls for burrows, build egg sacs, wrap prey, and temporarily hold sperm, among other applications.

All but about 150 species of spiders (in the families Uloboridae and Holarchaeidae, and the suborder Mesothelae) can inject venom to protect themselves or to kill and liquefy prey. Only up to 200 species, however, have bites that can pose health problems to humans.[1] Many larger species' bites may be painful, but will not produce lasting health concerns.

 

For more information go to:

http://en.wikipedia.org/wiki/Spiders