How do fireflies make light?

That night the power was off at Grandma's, so Na and Cú Bông sat out on the veranda. Down by the pond, in the long grass, small lights kept blinking. Na counted seven before they went out and lit up somewhere else.

Grandma lit the old oil lamp and set it on the doorstep. Cú Bông looked from the flame to the garden and guessed that each firefly carried a tiny flame too. And flames are hot.

A firefly strayed onto the veranda and landed on a dry almond leaf by Na's hand. It kept glowing, yet the leaf didn't scorch, and not a wisp of smoke rose from it. Cú Bông began to wonder whether a firefly made light some other way.

A firefly's light comes from the last few segments of its abdomen, a part known as the lantern. Inside, oxygen from the air takes part in a chemical reaction, and the reaction gives off light. It gives off very little heat. That's why it's called cold light.

In some glowing firefly species, males and females use flashes to recognise one another. Males often flash as they fly. Females often rest low in the grass and may flash back when they recognise their own species' pattern. Patterns differ between species: how many flashes, how long, and the gaps between.

Pick one of the example patterns for the male, press Flash, then watch the grass. In some species a female may answer a male of her own kind, though not every time.

In the lantern, oxygen takes part in a chemical reaction that gives off light but very little heat. In some glowing firefly species, flash patterns help males and females recognise one another.