One of the more peaceful forms of summer entertainment is sitting out in the yard watching fireflies do their light show at dusk. And who hasn’t as a child stalked and captured “lightnin bugs” them in a jar? Fireflies are real standouts of the insect world, so let me illuminate you (heh).
There are over 2000 different species of fireflies on the planet, and the most familiar one in our area is the Common Eastern Firefly (Photinus pyralis). They are readily identifiable by their trademark flashing light, but in daylight, they are a ½ to ¾ inch long beetles with black wings and a red area near the head with a black spot in it. It’s the male you see flying and blinking at night, as the female rarely flies, even though she has wings.
To cover the life of the firefly, let’s start with the bling… that winking yellow light. While it catches the eye of us humans readily enough, the aerial light show the male puts on is really to attract the attention of the female sitting on the ground looking up at him. The light signal varies among firefly species, but ours traces a J shape. The male will hover above the ground, then drop suddenly, flash near the bottom of his fall and then swoop back up, letting the light slowly fade as he rises. If a female likes what she sees, she responds by flashing at a fixed time delay after the male’s last flash. A short flash dialogue may ensue (a form of flirting I’m sure), helping the male locate her position so he can descend to mate. Flashing of the eastern firefly is most active at dusk, earlier than most other fireflies. Their flash is yellow, while others emit green.
A few days after mating, a female lays her fertilized eggs on or just below the surface of the ground. The eggs hatch 3-4 weeks later and the larvae (called glowworms) spend the rest of the summer underground hunting and feeding on earthworms, other insect larvae, slugs, and snails. After overwintering, they resume feeding in the spring and eventually pupate and emerge as adults to start the cycle over.
Chemists are fascinated by fireflies, because the glow is produced by a chemical reaction (called bioluminescence) that produces essentially no heat. The glow is so energy efficient that 90% of the energy used is converted to visible light. By comparison, an L.E.D. light, the most efficient light science has come up with so far, only converts 20% of the total energy used to visible light. The chemical reaction occurs in something called a photic organ located on the abdomen. The process is complicated, but in a nutshell when an enzyme called luciferase reacts with something called luciferin, you get light.
Tropical fireflies routinely synchronize their flashes among large groups, called biological synchronicity by the science guys. A few places in the United States also have this occurring, most noteworthy being at Elmont in the Smoky Mountain National Park, where they will suddenly all blink in unison. It draws quite a crowd.