Spider behavior Spider behavior Spider behavior refers to the range of behaviors and activities performed by spiders. Spiders 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 groups of organisms which is reflected in their large diversity of behavior. Almost all known spider species are predators, mostly preying on insects and on other spiders, although a few species also take vertebrates such as frogs, lizards, fish, and even birds and bats. Spiders' guts are too narrow to take solids, and
Opabinia family tree is that modern tardigrades may be "Opabinia"s closest living evolutionary relatives. Although Zhang and Briggs (2007) disagreed with Budd's diagnosis that "Opabinia"s "triangles" were legs, the resemblance they saw between "Opabinia"s lobe+gill arrangement and arthropods' biramous limbs led them to conclude that "Opabinia" was very closely related to arthropods. In fact they presented a family tree very similar to Budd's except that theirs did not mention tardigrades. "Opabinia" made it clear how little was known about soft-bodied animals, which do not usually leave fossils. When Whittington described it in the mid-1970s, there was already a vigorous debate about