Diurnal

Definition

Active during daylight hours; exhibiting a circadian activity pattern centered on the photophase. In arthropods, diurnality typically involves visual hunting, thermoregulatory basking, or pollinator-mediated resource acquisition that exploits daytime conditions. Contrasts with nocturnal (night-active) and crepuscular (dawn/dusk-active) patterns; some species shift between states seasonally or developmentally.

Etymology

Latin diurnus, from dies 'day'

Example

Adult dragonflies (Anisoptera) are strongly diurnal predators: their large compound eyes and high metabolic requirements for flight depend on daytime warmth and light to detect and intercept prey.

Related Terms

• Nocturnal
• Crepuscular
• Circadian rhythm
• Photophase
• Activity pattern
• thermoregulation

Usage Notes

Applied to organisms, populations, or specific behaviors (e.g., 'diurnal foraging'). Not synonymous with 'daily' in the sense of 'every 24 hours'—diurnal specifically denotes daytime activity. Some species are cathemeral (irregularly active day and night), complicating simple classification. In collection contexts, 'diurnal' methods include sweep-netting or visual searching during daylight, as opposed to light-trapping for nocturnal species.