Firefly

The living lantern of summer nights

A firefly is a beetle that makes its own light! In its belly is a substance that glows with cold light when it meets air — hold one and it won't burn you. Fireflies send each other 'signals': every species flashes in its own rhythm. In Japan, people go to the riverside on summer nights just to watch them.

Fireflies (Lampyridae) number over 2,000 species everywhere except Antarctica; Uzbekistan has a few (Lampyris). The light is bioluminescence: luciferin + the enzyme luciferase + oxygen → nearly 100% efficient 'cold light' (a light bulb manages 10%). Each species flashes in its own rhythm — a code for finding mates; females of some species 'fake' another species' code and eat the fooled males. Larvae glow too, warning predators 'I'm toxic'; they eat snails. Light pollution and pesticides are reducing numbers in many places. In Southeast Asia whole trees flash in sync.

Fun facts

• A firefly's light is nearly 100% efficient — a light bulb wastes 90% as heat.
• Some females fake another species' signal and eat the males.
• In Asia thousands of fireflies on one tree flash in unison.