Fireflies lighting up the summer nights

While over 2,000 species of fireflies exist throughout the world, less than a half dozen species are commonly seen in our area. These winged beetles of the order Coleoptera and family Lampyridae are known to many as lightning bugs from their night time luminescent flashes. About 3⁄4 inches in length, both male and female fireflies produce flash patterns that are different for each species and vary by sex. The flashes are signals used to attract mates.

Fireflies, as with other bioluminescent animals, produce a chemical called luciferin, which produces light when oxidized in the presence of an enzyme catalyst. The luciferin component of firefly bioluminescence was first isolated in 1949 at the Johns Hopkins University Chemistry Department. The most common firefly species seen in our area, Photinus pyralis, the common eastern firefly, and Photuris pennsylvanica, the Pennsylvania firefly, emit yellow-green light. While all fireflies use the same luciferin, variations in pH and chemistry cause different light colors to exist between some species. The peak months for fireflies in Frederick County are June and July.

Credit: - Bruce Marlin

Nocturnal, yet most active in twilight and early night, males locate females by a series of unique flashes to which the females respond with similar flashes. The eastern firefly, the most common species seen in our area, mainly flies close to the ground, with the males using a “j” – shaped flight pattern, flashing on the upward part of the “j.” Males flash roughly at six-second intervals, with the females flashing with about a two-second delay. The females typically will remain on the ground and will elevate the glowing part of the abdomen towards the flying male firefly.

Photinus fireflies do not feed as adults. The ground-dwelling larvae of fireflies generally glow and are sometimes referred to as glowworms. Firefly larvae should not be confused with another type of beetle species of the family Phegodidae, native but not commonly seen in our area, of which the females and larvae also possess bioluminescent organs and glow. These are similarly referred to as glowworms, as the females dwell on the ground.

After mating, the female firefly lays her eggs just under the surface of the ground. The eggs hatch in three to four weeks, with the larvae feeding on other insect larvae and invertebrates like snails and slugs. Fireflies hibernate over winter in the larval stage, feeding in the spring for a few weeks until pupating and emerging as adults. Similar to other beetles, fireflies have a disagreeable taste to many predators, with scientific opinion that the light emissions may also be a defense mechanism by which potential predators may avoid feeding on fireflies. While not considered harmful to humans, it is recommended that fireflies not be eaten, as some species in addition to having a disagreeable taste may have a mild toxicity.

Article by Tom Anderson, FCFCDB member

Nature Notes for 7/21/2013