Spiders are arachnids, not insects. The arachnid family includes scorpions, mites, ticks and harvestmen. The differences between arachnids and insects are mostly anatomical. Arachnids have 8 legs, insects 6; an insect's body is comprised of 3 segments, head, thorax and abdomen, an arachnids of 2, cephalothorax and abdomen; insects have compound eyes, arachnids simple eyes; insects have antennae, arachnids don't; many insects have wings, arachnids never; insects have mandibles, arachnids have chelicerae (the appendages in front of the mouth of an arachnid, of course); insects undergo some form of metamorphosis, arachnids don’t. So, is the difference clear?