Well in the grand scheme of living things man breaks down everything into categories. In the animal Kingdom under the Phylum Arthropoda there is a Class called Insecta. From here on out it will start to get difficult. Identifying insects gets complicated because they change. Not just a little change but great big ones.
Aquatic insects go from being water breathing bottom crawlers to air breathing flies.
Some Coleoptera go from terrestrial juveniles to aquatic adults. This is called Metamorphosis, which means change. In aquatic insects there are two kinds of metamorphosis, complete metamorphosis and incomplete metamorphosis. I nsects that have complete metamorphosis go through four different stages. Those stages are egg, larva, pupa, and adult.