In some forests, thousands of fireflies flash in perfect unison.

For several seconds, an entire hillside may light up at once. Then everything goes dark. Moments later, the insects flash together again, creating waves of light that ripple through the trees.

Scientists believe this synchronized flashing helps males attract females more effectively. Instead of competing with one another, the insects briefly become part of a glowing chorus.

Not all fireflies synchronize their flashes. More than 2,000 species exist worldwide, and many use distinctive flash patterns to communicate. A male may flash while flying, and a female of the same species responds from the grass or a nearby branch.

The display becomes even more surprising when you consider that adult fireflies have little time to waste. Most fireflies spend one to two years as larvae, but many adults live only a few weeks. Some species do not feed at all as adults, while others eat very little. Their brief adult lives are focused primarily on finding a mate and reproducing.

Some female fireflies add a darker twist. Females of certain predatory species imitate the flash signals of other fireflies, luring unsuspecting males closer. What looks like courtship can become an ambush.

The chemistry behind the glow is just as interesting as the display itself. Fireflies produce light through a chemical reaction involving an enzyme called luciferase that converts nearly all of its energy into light rather than heat.

That same enzyme has become an important tool for scientists. Researchers use luciferase to help track cells, monitor biological processes, and study diseases, allowing them to observe events that would otherwise be difficult to see.

For many fireflies, those few weeks of summer are the only chance they will ever have to find a mate. Every flash matters.