Nature's Quiet Fireworks
Who, as a child, has not enjoyed the fun of catching these light flashers in a jar on a warm summer evening? Fireflies are a good introduction to the fascinating world of insects for children. They don't bite, sting, pinch, carry disease, or even fly very fast, but they do create the magic of cold light on a twinkling midsummer’s night.
You may know them as lightning bugs, glowworms, or fireflies, but they are not bugs, flies, or worms; they are really beetles in the family Lampyridae. The firefly species Photuris pensylvanica, commonly called the Pennsylvania firefly, is the official state insect of Pennsylvania.
In 1973, the Baltimore checkerspot butterfly was designated the state insect of Maryland. Students at Highland Park Elementary School in Upper Darby, Delaware County, discovered this fact, and that Pennsylvania did not have a state insect. The students submitted the Pennsylvania firefly to the General Assembly for consideration, and thanks to their efforts, it became Pennsylvania's state insect on April 10, 1974.
There are about 2000 known species of fireflies around the world, in every continent except Antarctica, and more species are still being discovered. The locus of lightning bugs is warm, moist tropical environments, such as Costa Rica, which is home to at least 80 species. North American species number about 170, with about 33 species currently known in Pennsylvania.
In 2026, Pennsylvania's Department of Conservation and Natural Resources (DCNR) is funding a firefly inventory in Pennsylvania. Entomologists will survey areas such as the Allegheny National Forest to map the locations, diversity, and population numbers of firefly species, and possibly identify species previously unknown in the state. Their aim is to create an information database to help guide future conservation efforts, as fireflies face increasing pressures in a changing environment.
Lightning bugs prefer moist and humid areas for egg and larval development, so weather conditions and soil moisture will also affect their numbers from year to year. They thrive in forests, fields, and wetlands near lakes, streams, and rivers.
The females lay eggs in moist soil, and the larvae that emerge, sowbug-like in appearance, are voracious predators of slugs, snails, and earthworms. Eggs and larvae of some species also glow, hence the name "glowworm." The larvae live in soil and leaf litter for 1 to 2 years and feed by injecting paralyzing digestive juices into their prey and then sucking out the body contents. In spring, they pupate in small mud balls and then emerge as adults in early summer. The adults live for only a few weeks and die after mating. During their short lives, adults either feed on nectar or pollen or don't eat at all. Some 'femme fatale' females attract and eat male fireflies of other species.
The bioluminescence produced by fireflies is cold light. It is almost 100% light, creating virtually no heat. This unique light is generated in special organs located on the abdomen of fireflies by two rare chemicals, luciferin and luciferase. Together with oxygen and a body chemical called ATP (adenosine triphosphate), these chemicals are converted into energy.
These "taillights" are flashed on and off by fireflies to attract mates. They are also used to signal danger or a warning. During the day, adult fireflies rest on plants near the ground. At dusk, the males start flying upward and flashing, looking for responsive females, who perch, waiting, on grass or leaves. Most of the fireflies you see flying are males. Each species of firefly has a unique flashing pattern called "flash trails" used by the males. Females respond with a single flash only, which is timed to a precise interval to correspond to the flash of an appropriate mate.
In recent years, people in many places have noticed a decline in the number of fireflies observed on summer evenings. Although scientists and researchers lack long-term data to confirm population declines in many areas, it is not hard to identify certain human-related activities as possible culprits. From the 1950s to the 1970s, huge numbers of fireflies were harvested from the wild for their luciferase, which was used in medical research. Loss of firefly habitat, due to land development and draining of wet areas, has also contributed. Light pollution is a factor because it can disrupt the light-dependent mating behavior of many fireflies. Fireflies also face threats from pesticide usage and climate change.
A few things homeowners and gardeners can do to help fireflies include turning off outdoor lighting during evening hours, reducing pesticide use in the garden, mowing grass to a height of 3 to 4 inches, and, in autumn, leaving fallen leaves on the ground in your landscape. That leaf litter provides shelter for glowworms and other beneficial insects. It also makes a free, useful mulch for flower beds and vegetable gardens.
Whether you know them as lightning bugs or fireflies, they are amazing insects. Let’s keep the magic of Pennsylvania's state insect alive so that their midsummer fireworks continue to spark joy in children and adults alike.
