Fireflies, also known as lightning bugs or glowworms, are actually beetles in the Lampyridae family—a fitting name for a species best known for its light (Lampyridae is Latin for “shining light”). Most species use bioluminescent light to communicate with each other, primarily to attract mates, but sometimes to signal alarm, or send a warning, or even to attract food— in the form of other fireflies! The light comes from an organ on the underside of the abdomen, in which oxygen reacts with a light-emitting biological pigment called luciferin in the presence of an enzyme called luciferase to emit photons--elementary particles of light. Other species—our “dark fireflies”—are active during the day and appear to communicate with chemical pheromones.
Fireflies can be found in both temperature and tropical regions all over the world, with nearly 2,000 species described from every continent except Antarctica. Over 120 species occur in the US and Canada, including all lower 48 states and many Canadian provinces. Fireflies are some of our most cherished and celebrated insects. They are found in art, literature, and cultural origin stories. To some, they merely signal the beginning of summer. To others, they symbolize the souls of the departed, or bad luck, or hope in the darkness. Fireflies give off a friendly vibe. They do not sting or bite, and they will not eat your crops or become a pest in the garden. They have an almost magical quality of lighting up the dark.
Biology and Life Cycle
Fireflies can be found in a wide range of habitats, from prairies and old fields to forests, desert canyons, and salt-spray wetlands. However, they all require moisture of some kind. Fireflies undergo complete metamorphosis, from egg to larva to pupa to adult. Most species live only a few weeks as adults, but can live up to two years as larvae. Although adult males are generally capable of flight, the females of many species are flight-less— they do not have wings and actually look more like grubs than true adults. They live in burrows in the ground and emerge at night to glow softly, waiting for males. Most larvae also live underground. In some species, such as those in the genus Pleotomodes, this subterranean lifestyle is taken to the extreme— both larvae and female adults live in ant nests. In contrast, the larvae of some species of Pyractomena forgo underground living and instead pupate on the bark of trees.
The diet of firefly larvae is composed primarily of soft-bodied invertebrates such as snails, slugs, and earthworms. Many species do not eat during their short time as adults, but there are exceptions. Among the most notable are females of the genus Photuris, which flash not only for their own males but also for those of another species. When an unsuspecting male arrives expecting to mate, he is instead eaten by the female; this behavior has earned Photuris females the nickname femmes fatales. Other species have been observed nectaring on milkweeds, and both pollen and flower nectar may be an important nutrient source for some adults.
Conservation Status and Extinction Risks
Fireflies are well loved, but they may be in trouble. Across the globe, people are reporting that fireflies appear to be less common than they used to be, and some researchers have documented local extirpations. Unfortunately, there has been little systematic monitoring of species population sizes and trends, making it difficult to determine quantitatively whether and to what extent populations are in decline. Even so, we know that some of the habitats that fireflies depend on are disappearing, and several other threats have been identified, including light pollution, pesticides, poor water quality, over-collection for the medical trade, and invasive species. Climate change and associated droughts, as well as rising sea levels for some species that occur in coastal areas, are of particular concern.
What We’re Doing
Prompted by anecdotal reports of decline, the Xerces Society has embarked on an effort to evaluate the current state of knowledge on the conservation status and extinction risk of fireflies in the United States and Canada. We have learned that while many studies have been published on firefly reproduction, behavior, and physiology, relatively little information exists on the status of populations and the life histories of individual species. Baseline data are scarce, and firefly taxonomy is in flux, with a number of well-known groups awaiting reassessment and newly discovered but undescribed species not yet named.
With this information, we are embarking on a campaign to better understand the status of these fireflies by working with researchers across North America and the world and working to educate land managers, farmers, and the public about how we can all conserve habitat so these animals will continue to delight future generations.