Insects are members of the animal class Insecta within the  phylum Arthropoda.  As arthropods they lack a backbone, have an external skeleton,  a segmented body and jointed appendages.

Insects are further characterized as having a three part body, three pairs of jointed appendages, compound eyes and two antennae. These animals are the most numerous species in most ecosystems except the oceans where another arthropod, the crustaceans, predominate. It is estimated that there are more than a million existing species of insects and that they represent the majority of all known living organisms.

Insects are often considered to be pests because they  may transmit disease, act as parasites and cause damage  to food sources. In contrast, insects may be ecologically  beneficial as well. Some insects play an important role in the pollination of flowering plants and are cultivated to assist in pollination management. Insects may also produce commercially important products and are cultivated for this purpose as well. They can also act as a food source for humans and other animals as well as for insects. In this regard, they may benefit agriculture by eating other insects that damage crops and other food sources. Insects are the single largest consumer of other insects and therefore play an important role in keeping their population growth under control.