Insects range from virtualy microscopic to nearly palm-sized. I used my diopter attachment to magnify this small Red Ant. This photo shows the three body parts that every insect has: the head, the thorax and the abdomen. The head contains the large black compound eyes, three tiny simple eyes (barely visible above the compound eyes), the antennae and the chewing mandibles. The thorax contains the 6 legs. If the ant had wings, they would be attached to the thorax too. The large abdomen is where the digestive, circulatory, respiratory, and reproductive systems are located. Insects don't breathe through their mouth and they don't have a nose, so they have to take in oxygen through small holes in the abdomen called spiracles. The air flows through the spiracles and into tiny, branching trachaea that go all over the insect's body.
Insects are classified by orders which reflect the type of wings a particular group has.