In animal behavior, diurnality is an animal that is active during the daytime and rests during the night. Animals that are not diurnal are either nocturnal (active at night) or crepuscular (active primarily during twilight, i.e., at dusk and dawn).  Many animal species are diurnal, including many mammals, insects and birds. The diurnal pattern is often controlled internally by the circadian rhythm (endogenous rhythm) of the animal. In some animals, especially insects, external patterns of the environment control the activity (exogenous rhythms).
Some mainly nocturnal or crepuscular animals have been domesticated as pets and have changed into diurnal animals to coincide with the cycle of human life. Examples are pet dogs and cats, which are derived from the wolf and the wild cat. However these animals may exhibit their species' original behaviour when they are born feral.
- Gullan, P.J. and P.S. Cranston, 1994. The Insects: An Outline of Entomology. Chapman and Hall London. pg. 115.
- Gullan and Cranston.