Headlight beetle's glowing path caught in time-lapse photo

Cristobal Serrano

By Leah Crane

IT’S like a message scrawled in light. This time-lapse image, taken over 30 seconds in a Costa Rican cloud forest, shows a headlight beetle’s meandering path along a leaf.

The insect’s “headlights” – two bioluminescent spots just behind its actual head (see image below) – gleam steadily as it wanders undisturbed, as does a third, hidden bright area under its abdomen.

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The largest and brightest of the bioluminescent insects, headlight beetles can reach 4 centimetres in length and glow with a brightness of around one-fortieth that of a candle. If anything gets too close, it can brighten its light to try to scare away the possible predator. This ability to dial its luminescence up and down can also be useful for luring prey. Grown headlight beetles are mostly vegetarian (with the exception of the occasional aphid), but larvae often devour other insects attracted to their gentle glow.

Brightness isn’t always safe for a headlight beetle, though – trap enough of them and you can light a whole room.

This article appeared in print under the headline “Glow in the dark”