Any one of numerous species of arachnids comprising the
   order Araneina. Spiders have the mandibles converted into poison fangs,
   or falcers. The abdomen is large and not segmented, with two or three
   pairs of spinnerets near the end, by means of which they spin threads
   of silk to form cocoons, or nests, to protect their eggs and young.
   Many species spin also complex webs to entrap the insects upon which
   they prey. The eyes are usually eight in number (rarely six), and are
   situated on the back of the cephalothorax. See Illust. under Araneina.