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Flickers of Light in the Summer Night

Fireflies’ luminescence is 100% efficient

Tiny golden-yellow lights flicker on, off, on, off.
    Watching them brings memories of childhood.
    Back in the days when I’d play outside from summer sun-up to after sundown, fireflies kept me company at night.
    Reading kept me company, too.
    P.D. Eastman’s Sam and the Firefly was a favorite.
    I’d pretend I was Sam the owl, helping Gus the firefly. I’d catch the flickering lights in mid-air, and put them in a pickle jar — with holes poked in the lid for air — then release them back into the warm summer sky.
    I imagined that fireflies talk to each other with light, and I was right. They emit light to attract mates, to defend territory and to warn away predators.
    These creatures are the world’s most efficient lights. One hundred percent of their energy is emitted as light. Compare that to an incandescent bulb, which emits 10 percent of its energy as light and the rest as heat, or a fluorescent bulb, which emits 90 percent of its energy as light but still 10 percent as heat. Because it produces no heat, firefly light is known as cold light.
    Inside the firefly’s tail are two chemicals — luciferase and luciferin. Luciferin is heat resistant, and under the right conditions it glows. Luciferase is an enzyme that triggers light emission. ATP, a chemical within the firefly’s body, converts to energy and initiates the glow.
    Every animal has ATP in its cells in amounts that are more or less constant, or should be. In diseased cells, the amount of ATP may be abnormal. The chemicals from fireflies are injected into diseased cells to detect cellular changes resulting from diseases from cancer to muscular dystrophy.
    Electronic detectors containing these chemicals have been fitted into spacecraft to detect life in outer space. On earth, the chemicals also mark food spoilage and bacterial contamination.
    Fireflies love warm, humid areas. They thrive in forests, fields and marshes near lakes, rivers, ponds, streams and vernal pools. They live only long enough to mate and lay eggs.
    So they’ll be back next summer, in Maryland and in every continent except Antarctica.