Behavior can be defined as anything that an individual does during its life, involving action in response to a stimulus. Eating behavior is stimulated by hunger; sleeping or resting behavior is in response to fatigue; escape is a response to attack and reproductive behavior is in response to physiological urges and stimulation by members of the opposite sex. Throughout the life of an individual insect it is behaving constantly in one way or another, making behavior a large and important subject.

Many behaviors are in response to external stimuli, part of the environment, making them ecologically relevant, and behavioral ecology is an important part of ecological understanding. Understanding much of behavior results from the study of how species are adapted to the problems of survival and reproduction, and how natural selection shapes the trajectory of a lineage through the costs and benefits, the opportunities and constraints, of any particular genetic and phenotypic change in that lineage.