Speaking of Nature: Fireflies
The month of July started out as though we were being punished for some forgotten indiscretion committed long ago. It rained and it rained. Then it got hot and the water in the saturated soil turned into vapor under the relentless sun. The daytime heat and humidity were downright punitive, which made the relative cool of the evenings pure heaven.
My house is situated on a hillside that gently slopes to the south. I have a deck that starts out at ground level on the north side of the house, but is eventually 12 feet above the lawn by the time it wraps around to the south side. The hill continues to slope down and away from the house for a couple hundred yards before leveling off at the edge of a beautiful woodland. Between the porch and the woods there is a stretch of lawn and then a somewhat permanent wet meadow.
Ever since I moved into this house, I have let some of the lawn go back to tall grasses and it is upon these grasses that I like gaze as I sit on the deck and soak up the sultry atmosphere of a summer evening. As pleasant as the dusk hours are, however, I am usually anxious for darkness to fall, for this is when the action really begins.
With all of this tall grass and open space so close, the month of July has more than just fireworks to offer. Every night, as the light fades, nature puts on her own fireworks display with the role of pyrotechnician being played by fireflies. What could be more fun than watching fireflies? Catching them, of course! But it turns out that the act of capturing a firefly is much easier than identifying one.
Evolution is a wondrous process and it has produced some truly remarkable organisms on this planet. Bioluminescence is an incredible solution to the problem of communicating at night. Male fireflies blink out their Aldis-lamp love songs in perfect silence and females blink their responses in return. I cannot help but think of World War II-era warships cruising the oceans of the 1940s and communicating in similar fashion. The fireflies’ songs are so much nicer to contemplate, however.
With such a clever methodology at their disposal, it should come as no surprise that fireflies have been rather successful out there in the dark. In fact, they have been so successful for so long that North America has 136 different species of fireflies divided up amongst 20 different genera. There are so many different types that they have warranted their very own Family (Lampyridae), the members of which share some very distinctive features.
When seen from above, the heads of fireflies are obscured by a flattened helmet of shell called a “protonum.” This is a feature common in almost all beetles, but its extension to cover the head, the way the bill of a baseball cap extends out over your face, is not. One of the photos I have provided shows antennae of the firefly sticking out from under the protonum.
Most insects are equipped with two pairs of wings, but in beetles the first set has undergone some changes so they can serve as a protective shell. Scientists being scientists, they came up with a special word for these specialized front wings and they are known as “elytra.” The different firefly genera all have slightly different configurations with their elytra. By examining the photo, you can find a few clues that will help us identify the insect down to the species level.
Note how the edges of the elytra on this specimen are generally bow shaped. This feature eliminates the genus Photinus, which is a fortunate thing that I will explain a little later. Note also that the elytra are dark, with shallow “striae,” or grooves, that run down the length of their glossy surfaces. Finally, note the coloration of the elytra; dark with light margins that produce a pattern not unlike that found on the shell of a graystripe sunflower seed. All point to a member of the genus Photuris, and I am going to take a stab at identifying this firefly as Photuris pennsylvanicus — the Pennsylvania firefly.
With 28 different species in the Photuris genus, however, it is not at all impossible that I have erred in my identification. All of the books at my disposal mention fireflies at the genus level save one — my trusty old copy of the Audubon Field Guide to North American Insects and Spiders. My Peterson Guide to Beetles informs me that Photinus and Photuris are the genera most readily collected fireflies, but the Audubon guide mentions only the Pennsylvania firefly for Photuris, so I am guessing it is the most common.
Members of the two genera do look rather similar in appearance, which made my identification a little tricky. For a firefly, however, and in particular a male firefly, an identification mixup can turn out quite badly. The reason is one that is purely sinister, but the males that make the mistakes don’t often live to tell the tale.
Adults in the Photinus genus don’t eat anything. As larvae they feast on slugs, snails, and the soft-bodied larvae of other insects. They then bury themselves in moist soil and start to pupate, which allows them to go dormant in the winter without starving. In the summer, the pupae emerge as adult beetles and set about their blinking. Males of each species have their own coded pattern so they attract the attention of the right sort of females. The females, in turn, blink out the right sort of response to attract the proper males. At least this is how it usually goes.
In the Photuris genus there is some trickery. Adults of the Photuris are predators and will attack and eat the same snails, slugs and larvae as the larvae. However, females in the Photuris genus will also change their blinking pattern so they appear to be Photinus females. An optimistic Photinus male, blinded to any morphological differences by the darkness of night, may zip in with confidence because he thinks he’s about to get lucky, but all that changes when he finds open jaws instead of open arms. Photinus females are so good at this trick that they can even attract males from other firefly genera.
Most amazing of all, however, is that there appears to be at least one genus of fireflies that has abandoned the blinking altogether. The members of the genus Ellychnia are only active during the daytime hours because they don’t blink at all. The other fireflies are equipped with organs at the ends of their segmented abdomens that act very much like glowsticks. Light is produced with virtually no heat, which avoids overheating or, even worse, cooking yourself to death. That would bring a whole new meaning to the phrase, “man is she hot.”
The breeding season of our fireflies, whether they be innocent Photinus or deadly Photuris, will end shortly. If you have any chance at all, I would encourage you to go out at night and enjoy these wonderful beetle as they participate in a very complicated but mostly effective method of looking for love.
Bill Danielson has worked as a naturalist for 16 years. In that time, he has been a national park ranger, a wildlife biologist and a field researcher. He currently works as a high school chemistry and biology teacher. To contact Bill, or to learn more about his writing, visit www.speakingofnature.com