Six and Eight Legs
An insect’s body is divided into three main parts: the head; the middle section, called the thorax; and the end section, called the abdomen. A spider's body has two segments: a cephalothorax and an abdomen. Insects have a brain, a nervous system, a heart, a gut for digestion, and tubes called tracheae to breathe oxygen. They have two antennae and six legs, both of which have special organs on them to sense sound vibrations and movement, and to "taste" and "smell" food (although they don’t have taste buds and noses like we do). Spiders have eight legs and, in general, have "simple" eyes instead of the "compound" eyes that give many insects much better vision.
Most insects, such as beetles, wasps, and flies, go through complete metamorphosis. They begin life as an egg that hatches to a larva. The larva eats, grows, and sheds, then turns into a pupa in which chemical changes take place. The final stage is changing into the adult insect, which is able to reproduce. In more primitive insects, such as grasshoppers and stick insects, another type of development is used. This process is called incomplete metamorphosis where the insect hatches from the egg as a miniature version of the adult. The insect continues to grow, and every time it molts it gets larger until it reaches adulthood.