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
Arthropod gills that were very different from those of arthropods. This reasoning implies that "Parapeytoia", which has legs and a backward-pointing mouth like that of the earliest arthropods, is a more credible closest relative of arthropods than is "Anomalocaris". In 2006, they suggested that arthropods were more closely related to lobopods and tardigrades than to anomalocarids. In 2014, research indicated that tardigrades were more closely related to arthropods than velvet worms. Higher up the "family tree", the Annelida have traditionally been considered the closest relatives of the Panarthropoda, since both groups have segmented bodies, and the combination of these groups was