Scientific Name: Photuris pennsylvanicus
Common Name: Pennsylvania Firefly
(Information in this species page was gathered in part by Ms. Megan McAuley for an assignment in Biology 220W (Spring semester 2007)).
The Pennsylvania firefly (Photuris pennsylvanicus) (also called the “Lightning bug”) is a cherished feature of warm Pennsylvania summer evenings. Its pulsing pinpoints of yellow and green light make the dark woodlands, fields, and gardens come alive with movement and possibilities. The firefly was named the state insect of Pennsylvania in 1974.
Classification and Appearance
The “firefly,” though, is not really a fly at all. It is a beetle in the family Lampyridae that, along with several hundred other closely related “firefly” species, has the remarkable ability, in all of its life stages, to biologically generate light. The adult beetle, which is the form most familiar to people, is ½ to ¾ inch in length, with a flattened body that is predominately black in color with yellow highlights and prominent red spots on the back of its thorax. It has large eyes and long antennae and flies in a gentle, hovering manner. The light generating parts of these adults are in the terminal segments of their abdomens. The adult firefly has long, curved mandibles that suggest a predaceous life style, but only a few species have been shown to actually consume anything other than flower nectar or pollen. The less well known larvae of the firefly, called “glow worms,” live in leaf litter and are voracious predators. They eat other insects, mites, earthworms, and even slugs and snails.
Using Light for Communication
The lights of the fireflies represent communication mechanisms. The female fireflies, which are predominantly sessile, perch on the vegetation in its habitat and generate a species specific sequence of light flashes that attract the much more mobile males. The males respond with an answering light sequence and zero in on the females in order to mate. A few species of firefly have been shown to mimic the light sequences of other species in order to draw unsuspecting males to waiting, predaceous females. These females not only gain energy from consuming the males of these other species but also can accumulate chemicals from their prey which help to protect them from their own predators. This behavior is called “aggressive mimicry.”
After mating in the late summer, the females lay their eggs one at a time on the surfaces of woody or leaf debris. The eggs hatch in a few weeks and the emerging larvae enter the soil/litter habitat where they actively feed on a wide range of invertebrates. In late fall, the larvae burrow into the soil or under the bark of woody stems where they overwinter. In the spring, they re-emerge and continue to actively feed on their diverse array of prey species. After a few weeks, they re-enter the soil and pupate. They then emerge from their pupal chambers in early to mid summer as adult fireflies.
The mechanism for the production of light in fireflies is mediated by the enzyme “luciferase.” High energy phosphates generated from food molecules are coupled via luciferase to the direct production of photons of light. This coupling is extremely efficient (90%+) and generates almost no waste energy (heat). The genes that regulate this light generation have been used in cancer research to mark and track metalizing cancerous cells.
There have been many reports of declining numbers of fireflies throughout North America. The widespread use of pesticides and herbicides, the loss of the leaf litter habitat required by larval life stages especially in suburban areas, and drought have all been proposed as factors in the decline of the firefly. It is hoped that this decline can be reversed so that we can all continue to have the pleasure of observing these unique and wonderful organisms.