Insects are the most varied and engrossing class of animals in the animal kingdom. The insects are animals from the arthropoda phylum , meaning that they have bilateral symmetry, a body made of jointed rings, exoskeletons, and a heart and nervous system. The arthropoda phylum is the biggest phylum in the animal kingdom. All insects have three pairs of legs and adult wings. Many people believe that spiders are insects, but, in fact, they are not.
Spiders are arachnids, a group which includes all mites.
It is believed that insects originated in the seas. The first group of arthropoda were believed to have come from the sea, and were originally descended from mollusks. The link people use to support this is the barnacle , which has arthropod and mollusk tendencies. Some of our modern insects have much more interesting extinct relatives. For instance, at one point there was a huge species of dragonfly that doesen't exist any longer.