Firefly: The beetle that glows

On summer nights, little lights flicker in the grass — those are fireflies. You might think of them as "glowing bugs", but a firefly is really a beetle with a talent for making light. Its light is not electricity; it is a gentle chemical trick inside its body.

Its body

A firefly's abdomen holds a group of special light-producing cells. Inside them are two things: luciferin and luciferase. Helped by luciferase, luciferin reacts with oxygen and turns almost all its energy into light. That "bulb" is close to one hundred per cent efficient — far better than an incandescent lamp — and it gives off very little heat. That is why it is called "cold light".

Fireflies are beetles, so they also have hard wing cases. When night falls, they switch on their little travelling lamp.

Where it lives and what it eats

Each firefly species flashes its own rhythm. Males flash on the wing, signalling "here I am" in a fixed light-code, while females usually answer from the grass with the matching code. The larvae live by streams and are fierce little hunters of snails. Larval fireflies glow too, though far more dimly than the adults.

Why it is becoming rarer

Fireflies are very sensitive to clean water and to genuine darkness. Streetlights and concrete riverbanks push them away from the places we know. To see them, we need to treasure clean, dark nights.

A note for grown-ups

On a summer night you could try "switching off the lights" with a child: true darkness really matters to fireflies. When you look, do not shine a torch straight at them — just wait quietly. That very act of waiting is itself a gentle lesson in nature.