Fireflies – the Bright Lights of Summer

Connie Holland
Adams County Master Gardener

Who among us as a child has never captured fireflies in a jar on a summer night? Their arrival in my yard each summer is eagerly awaited. Thus far, at peak firefly breeding time, the trees in my yard and adjacent fields at night are aglow with tiny flashing lights as though strung with tiny white electric lights. However, in some areas, their numbers are noticeably in decline, mostly due to loss of habitat and pesticide use.

Did you know that fireflies are actually beetles? They are members of the family Lampyridae. There are about 2,000 known firefly species. Since fireflies are nocturnal, during the day they spend most of their time on the ground or resting under plant leaves. At night, they crawl to the tops of blades of grass or into trees to signal for mates. These vantage points conceal the fireflies from predators and provide a good place for signaling.

Everyone knows how fireflies get their name, but many people do not know how the insects produce their recognizable glow. Fireflies have dedicated light organs that are located under the abdomen in their tails containing luciferase and luciferin, the two compounds that produce the light. Under the right conditions, luciferase is an enzyme that triggers light emission in the protein luciferin Because a firefly’s light produces no heat, it is referred to as a "cold light." A firefly’s light is the most energy efficient light in the world since 100% of the energy is emitted as light with no loss to heat.

Firefly light is usually intermittent, flashing in patterns unique to each species. Each blinking pattern is a signal that helps them find potential mates. Scientists are not sure how the insects regulate the process to turn their lights on and off. In addition to helping find a mate, their light may be as a defense mechanism that flashes a clear warning of the firefly’s unappetizing taste. In some firefly species, only males light up. In most, however, both sexes glow. The male signals while flying and females wait in trees, shrubs and grasses hoping to spot an attractive male. Females respond to the males with their own unique flash.

Female fireflies deposit their eggs in the ground where they hatch into larvae after three to four weeks. Firefly larvae glow just as their parents, only in this case, it is thought to be a defensive mechanism to warn off predators. The larvae of most firefly species are themselves predators, feeding on other larvae, snails, and slugs. Some have grooved jaws that can inject numbing digestive fluids directly into their prey. Firefly larvae feed until the end of summer and hibernate over the winter. Some burrow underground, while others find places on or under tree bark. They emerge in spring and, after several weeks of feeding, pupate and shortly emerge as adult fireflies. Adult fireflies dine on pollen and nectar while some firefly species are predatory.

Most firefly species have one thing in common, the need to be near standing water. In drier areas, they are found around wet or damp locations. Vernal pools and small depressions that hold water during firefly mating season provide the habitat fireflies need. Most species thrive in forests, fields or the areas between them. Almost no fireflies are found west of Kansas even though there are warm and humid areas to the west. No one knows exactly why.

In the plant and animal world, fireflies are not the only ones producing light. Some jellyfish and plankton glow via a complex green fluorescent protein. Genetic engineering even has manipulated plant genes to create light producing plants that actually shine in the dark, although dimly. The next time you see the twinkle of a firefly, think of what takes place to bring us this amazing and wonderful display.

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