Insects are a major group of arthropods and the most diverse group of animals on the Earth, with over a million described species—more than all other animal groups combined. Insects may be found in nearly all environments on the planet, although only a small number of species occur in the oceans where crustaceans tend to predominate instead. There are approximately 5,000 dra;nfly species, 2,000 praying mantis, 20,000 grasshopper, 170,000 butterfly and moth, 120,000 fly, 82,000 true bug, 360,000 beetle, and 110,000 bee, wasp and ant species described to date.

Estimates of the total number of current species, including those not yet known to science, range from two million to fifty million, with newer studies favouring a lower figure of about six to ten million. Adult modern insects range in size from a 0.139 mm (0.00547 in); Mymarid wasp to a 55.5 cm (21.9 in); long Stick insect. The heaviest documented insect is a Giant Weta (at 70 g, 2½ oz);, but other possible candidates include the ;liath beetles ;liathus ;liatus, ;liathus regius and Cerambycid beetles such as Titanus giganteus, though no one is certain which is truly the heaviest.