Fireflies or, if you prefer, lightning bugs, are neither flies nor bugs -- they are beetles in the family Lampyridae. Most fireflies are bioluminescent, meaning they can produce light in special organs and they spangle our yards, gardens, woods, and meadows with flashing lights on late spring through mid-summer evenings. They use chemical energy to produce light in a process that is nearly 100% efficient, as compared to the 10% or less efficiency of an incandescent light bulb. Fireflies use their lights to communicate with potential mates and warn predators that they taste bad. Firefly light shows, however, are a natural phenomenon at risk from light pollution, pesticides, habitat loss, poor water quality, invasive species, and climate change. The International Union for the Conservation of Nature lists a number of North American species as under threat. The good news is that we can help mitigate some of these threats in our own yards and gardens, neighborhoods, and communities.

Identification: fireflies are readily recognized at night, as they are the only bioluminescent flying insect in our region. However, not all adults produce light in their adult stage, and these darkflies are active in daytime. All firefly larvae are bioluminescent, but they cannot control their light to create distinctive flash patterns like adults. Some firefly pupae and eggs also glow. You can learn to identify the adults of some species by the their flash pattern. You might also see the intermittent glow of larvae on the ground in the spring or fall. Adults of three common genera in our region, Photinus, Photuris, and Pyractomena are distinguishable by the color of their lights: yellowish for Photinus, greenish for Photuris, and deep yellow to orange for Pyractomena. Also, Photinus generally flash earlier in the evening than Photuris and Pyractomena flash even later.

Fireflies are also readily recognized during the day, once you know what to look for. They are elongate beetles, ranging from 5 – 20 mm with a pair of long, serrate (saw-toothed) antennae and a pair of relatively large eyes. Seen from above, the head and part of the thorax is covered by a shield-like squarish plate, called a pronotum, that usually has yellow, orange, and/or red markings. Leathery forewings cover the rest of the body and are brown or black, often with yellow or orange margins. At the end of the underside of the abdomen, most fireflies have two or three yellow light producing organs, called lanterns. Adults of some firefly species, often called darkflies, have reduced or absent light producing organs and do not flash.

Range: fireflies are found throughout our region in a wide variety of habitats; some species can be very habitat-specific while others are more generalist in their habitat preferences. Numbers and species diversity tend to be greater where habitat is less disturbed, though some tolerate more urban conditions. According to the Loudoun Wildlife Conservancy, about 20 species are found in Northern Virginia. 

Breeding:  fireflies mate in our region from early spring through late-summer, but the peak breeding season is mid-spring through early-summer. If fireflies are flashing, you can be sure mating is going on, because flashing is all about signaling potential mates. Males make often elaborate flash displays in flight, while receptive females make simpler response flashes from the ground or a low perch. Depending on the species, the mating season lasts from one to two weeks to several months. They usually lay their eggs on or in soil, though some species lay eggs on plants. The larvae hatch out in about a month. Fireflies spend most of their lives in the larval stage, during which they hunt and consume prey. Fireflies pupate underground, in rotting logs, or sometimes in the furrows of tree bark, where they spend the winter. Adults emerge the following spring and summer and most live only a week or two, while some overwinter as adults. Fireflies complete their lifecycle in a year or less in our region.