Spiders are arachnids. Spiders are any of several orders of arachnids
having the abdomen usually unsegmented and constricted at the base, chelicerae
modified into poison fangs, and two or more pairs of abdominal spinnerets for
spinning threads of silk used in making cocoons for their eggs, nests for
themselves, and webs to catch prey.
There are field guides to various spiders available online.