Scientists Say: Crepuscular

These animals prefer the dim glow of twilight


Fireflies are crepuscular insects. The dim light of evening helps their flashes stand out.


Crepuscular (adjective, “Kreh-PUS-kew-lur”)

A word to describe an animal that is active in twilight — dusk or dawn. Animals active during the day are diurnal. Those active at night are nocturnal. Some animals in desert environments are crepuscular to avoid the heat of the day. Other animals — such as fireflies — are crepuscular so their flashing signals shine bright. 

In a sentence

When using an app that tracks fireflies, you might want to wait until dusk to capture the crepuscular bugs.

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Power Words

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app     Short for application , or a computer program designed for a specific task.

bug     The slang term for an insect. Sometimes it’s even used to refer to a germ.

crepuscular    An adjective that describes animals that are active during twilight.

diurnal   An adjective for some activity that is done during the day, or some organism that is active during the day.

environment     The sum of all of the things that exist around some organism or the process and the condition those things create for that organism or process. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature, humidity and placement of components in some electronics system or product.

nocturnal     An adjective for something that is done, occurring or active at night.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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