Nocturnal

Definition

Active during nighttime hours, with corresponding rest or inactivity during daylight; describes the daily activity rhythm (diel periodicity) of an organism. In entomology and arachnology, nocturnality is common in taxa that exploit night-blooming resources, avoid daytime predators or desiccation, or use olfactory and acoustic signals that function best in darkness. Contrast with diurnal (day-active) and crepuscular (dawn/dusk-active).

Etymology

From Latin nocturnus "of the night," from nox, noctis "night"

Example

Most saturniid moths are strictly nocturnal, emerging after sunset to locate mates by tracking female-emitted pheromones on night air currents; similarly, many wolf spiders (Lycosidae) hunt above ground only after dark to reduce avian predation risk.

Related Terms

• Diurnal
• Crepuscular
• Diel cycle
• Circadian
• Cathemeral
• Moth trap
• pheromone

Usage Notes

Applied to the organism, not the environment ("nocturnal moth," not "nocturnal forest"). Some species shift between nocturnal and diurnal activity seasonally or contextually; such plasticity is distinguished from obligate nocturnality. The noun form "nocturnality" describes the trait or phenomenon.