Spiders are terrestrial predators with eight-legs and hollow fangs for injecting venom. They are known for their ability to produce silk webs.

Like other arthropods, all the arachnids have an exoskeleton with jointed appendages, segmented bodies, bilateral symmetry, a ventral nerve cord, and a complete digestive system. Unlike members of many other arthropod groups, arachnids lack antennae and wings.

Spiders are the largest order of arachnids, and rank seventh in total species diversity with about 49,000 identified species, and likely more than twice as many more left to discover.