Summer is here and it’s time for warm nights full of bonfires, stories, and fireflies. Fireflies, or lightning bugs, are known for their evening glow called bioluminescence.

Inside the abdomen of the firefly is a light organ that contains all the chemical ingredients necessary to produce light: magnesium, ATP (the cell’s energy currency), luciferin (a molecule produced by fireflies), and luciferase (an enzyme). When oxygen is added to these components, like the snap of a glow stick, light is produced. However, in that split second between the snap and the glow, a few chemical steps occur.

All of these steps require the enzyme luciferase. Enzymes are proteins that help chemicals react. Luciferase has pockets where the previously described chemical ingredients can mix. In the first step, magnesium, ATP, and luciferin come together to produce a modified luciferin. Luciferase then twists to reveal a second pocket where the modified luciferin waits for the next step. Oxygen enters this second pocket of luciferase, where it transforms into a superoxide anion. This molecule is normally toxic, but luciferase is able to produce and use it so quickly that the firefly is unharmed. The superoxide anion crashes into the waiting luciferin creating an unstable intermediate that rapidly breaks apart and releases energy that we observe as light. All of these steps happen in less than a second!

Fireflies can glow in a few different colors – yellow, green, and red – although the same chemical reaction occurs for each. The color change is controlled by the pH level inside the light organ. At neutral or basic pH, the light is green or yellow. As the pH becomes more acidic, the light is red. “Blue ghost” fireflies, a rare species found only in the Appalachian forests of North Carolina, initially appear to break this rule. However, scientists have recently discovered that this blue color is due to a trick of the eyes, not a difference in chemistry!

Peer edited by Ana Cartaya

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