Spiders (
order Araneae) are air-breathing
arthropods that have eight legs and
chelicerae with fangs that inject
venom. They are the largest order of
arachnids and rank seventh in total species diversity among all other
orders of organisms. Spiders are found worldwide on every continent except for
Antarctica, and have become established in nearly every
habitat with the exceptions of air and sea colonization. , at least 45,700 spider
species, and 114
families have been recorded by
taxonomists. However, there has been dissension within the
scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
