Crepuscular

Definition

Active primarily during twilight periods at dawn (matutinal) and/or dusk (vespertine), as opposed to daytime (diurnal) or nighttime (nocturnal) activity. In entomology, crepuscular behavior is common among moths, certain beetles, and other insects that exploit the reduced predation risk and moderate temperatures of the crepuscular interval, sometimes extending activity into moonlit or heavily overcast conditions.

Etymology

From Latin crepusculum, meaning twilight or dusk.

Example

Many geometrid moths, dor beetles (Geotrupidae), and crepuscular darter dragonflies (Tholymis tillarga) forage or mate primarily during the brief light transitions between day and night.

Synonyms

• crepusculine
• twilight-active

Related Terms

• Diurnal
• Nocturnal
• matutinal
• vespertine
• circadian
• activity pattern
• diel cycle

Usage Notes

Strictly distinguishes from diurnal and nocturnal; some species described as crepuscular may show facultative extension into adjacent low-light periods. The term applies to the timing of surface activity, not necessarily to internal physiological rhythms. Contrast with cathemeral (irregular activity across day and night).