Figure 1 Adult Big Dipper firefly found on ground vegetation. Photo courtesy of Katja Schulz at https://commons.wikimedia.org/wiki/File:Common_Eastern_Firefly_(27858835340).jpg
The flickering of fireflies signals the beginning of warm summer nights. Although these common beetles evoke a sense of wonder in viewers, they are simply performing a luminescent courtship ritual that has evolved over millennia.
About 2,200 species of fireflies are known worldwide, with about 125 found in North America. The American Big Dipper firefly (Photinus pyralis) is the most commonly found species in Missouri (Figure 1). Adults of this firefly are about one-half inch long and have a red plate behind their head with a black spot in the center, a blackish brown body, and wing covers (elytra) outlined in yellow. The last section of the abdomen, which emits a flicker of light, is known as the lantern.
The glow of a firefly is produced when an organic substance called luciferin is oxidized in the presence of the luciferase enzyme, which releases energy as light. At dusk or during the early evening, Big Dipper firefly males display a J-shaped flash about every six seconds while hovering about two feet from the ground to attract a mate. Females are usually found in grass or other low-growing vegetation, waiting for an attractive mate. A female will flash back multiple times to the hovering male to signal that she will accept him or remains dark if she rejects the male.
The female Big Dipper firefly lays her eggs, which also glow briefly, on the soil surface. After 18 to 25 days, the eggs hatch, and the larvae, with two light-producing organs, begin feeding on snails, slugs, and worms in organic matter or underground. The larval stage lasts one to two years before the luminescent pupal stage, which lasts only about 9 to 15 days.
Firefly numbers are diminishing in some areas where their habitat is shrinking or where light pollution occurs. To preserve fireflies in residential areas, leave a bit of vegetation, such as grass clippings or leaf litter in a small area, which will retain moisture and attract fireflies and their potential food sources. Minimize the use of pesticides and use them only when needed. Limit outdoor lighting or use a motion sensor to trigger the lights when fireflies are active. If needed, use red light bulbs as this color is less disturbing to fireflies. Then, sit back, relax, and enjoy their ethereal beauty as they perform their courtship flickering in the night.