Spiders, which belong to the arachnid family, have eight legs and two main body parts: the cephalothorax (a combined head and thorax) and an abdomen. Insects are in a family of their own, have six legs and three major body parts: a head, thorax, and an abdomen. Insects have compound eyes and a jaw best adapted to chewing while spiders have simple eyes and a jaw used primarily for piercing its prey.