The fascinating firefly
One common sight on summer nights in the High Country is the appearance of flickering fireflies. Also known as lightning bugs, these insects in the beetle Family spend two to three years in the soil as larvae (juveniles) before emerging as adults to put on their light show. Fireflies are one of only a few living things on earth that can produce light in a process called bioluminescence. Their yellow or orange glow lights up our summer evenings and provides a great example of how insects communicate with each other. Let's explore this fascinating insect and find out not only what the fireflies "say" with their flashing light but also how they say it.
Insects communicate for many reasons, with a very common one being so that boys and girls can locate each other and find a mate. For fireflies, light is the method used to both locate potential mates and communicate interest in mating. The production of light in the back of the firefly involves actions of the insect nervous system, allowing control for how long and how often to flash in a period measured in seconds. The combination of flash duration, and how often to flash, varies between different fireflies, which is important since there are numerous species. Having a specific signal ensures the correct species locate each other.
So what does the firefly flash say? Though there are several firefly species in our area, a very common one illustrates what the message in the flash is. The firefly called the big dipper, Photinus pyralis, gets its name because the males dip into a J pattern between flashes. During the day, both the male and female beetles hang out on the ground waiting for the days light to fade. At dusk, the male dipper flies up to court a female, slowly increasing his height above ground and lighting his "lantern". Females wait on the ground and give a quick flash if interested in a courting male. The male then descends to the ground and mating may occur. From this interaction you can see that the guys are saying "choose me" based on the duration and how often they flash, and the girls are making the final decision on whether to mate or not.
One of the most dramatic night-time firefly shows you'll see is one put on by a species called synchronous fireflies, Photinus carolinus. For these beetles the males flash in unison for several seconds, followed by a period of non-flashing, which produces a dramatic effect. This is especially true if hundreds, or even thousands, of synchronous fireflies are present in a small area. Each year in mid-June people flock to the deep rich forests of the Great Smoky Mountains National Park near Elkmont to see this phenomenon. Viewing it has become so popular that a lottery system has been set up by the US National Park Service to limit who is eligible to see it. While the time for viewing this spectacular show has passed for this year, if you are interested in planning ahead for 2025 the following link provides information: https://www.nps.gov/grsm/learn/nature/fireflies.htm. Though the Smokies are a great place to see synchronous fireflies, you don't have to travel that far to experience their fascinating displays. Reports of synchronous fireflies in the Price Lake area off the Blue Ridge Parkway are common. I have even observed these fireflies behind my home near Boone in past years. Though they are not present every year, it's worth looking for them in your area. But for now- watch out for the tell-tale "J" of the big dipper as guys compete for girls using their easily recognizable flashes.
Summer evenings in the High Country offer not only a respite from day time heat, but also a great time to see how insects communicate in a most unique way by using light. Fireflies put on quite a show for us with their coordinated flashes, so we need to make sure the show continues each summer. Providing fireflies with plenty of good habitat, such as undisturbed and pesticide-free land is important. By doing so we can all look forward to pulling up a chair and watching these fascinating bugs light up our summer nights.
Sources:
Fireflies, glow-worms, and lightning bugs
L F Faust
The University of Georgia Press
2017