Insects belong in the animal kingdom. All life is divided into two main kingdoms: the animal kingdom and the plant kingdom. Kingdoms are further divide into phylums, and phylums are divided into classes, classes into orders, orders into families, families into genus and genus into species.
All members of the animal kingdom, or Metazoa, are multicellular eukaryotes that are heterotrophs, which basically means that the organism gets the majority of its nutritional requirements from complex organic substances. There are currently approximately 9 to 10 million species of organisms identified in the animal kingdom. Members of this kingdom were first identified through fossil evidence from the Cambrian explosion, which happened approximately 540 million years ago.
Insects are specifically categorized in the class Insecta. All members of this class have a segmented body that is divided into three separate and distinct regions known as the head, thorax and abdomen, have three pairs of legs, have one pair of antenna and may or may not have wings. All insects also have a hard exoskeleton that protects their vital organs.
Carolus Linnaeus, the "Father of Taxonomy," has been known as the scientist who first developed the classification system in the 1700s. Linnaeus collected over 40,000 specimens of plants, animals and shells in order to determine how to properly categorize them.