Some 34,000 species of spiders have been described. Most are terrestrial animals.
Spiders are predatory and prey mostly on insects.
The number and arrangement of these eyes are major considerations in the classification of species. The end segment of each chelicera is fanglike and is connected to a venom gland. The legs have seven segments. At the tip of the opisthosoma are several fingerlike structures, known as spinnerets, which produce viscous droplets of silk from the silk glands, forming threads. Spiders change little during growth, except in size.