Nostalgia is an ever more important part of my life these days. I get all fuzzy inside remembering warm summer evenings with fireflies as a child. Watching the dark blue velvet dusk turn all sparkly—like silent fireworks in the grass, or glittering clouds of fairy dust. Memory is a warpy sort of reservoir, an imperfect process that not only entertains old men but also records change and loss. Although I’m not aware of any official census, it seems to me there are fewer fireflies around than there used to be. I hardly ever see them anymore. . . but when I do, it’s just as special as ever.
Despite their common name, fireflies are really just winged beetles. Turns out, it’s a big world and there’s a few surprises to be discovered. Not all fireflies fly and not all of them light up. With over 2,000 species across the globe, it makes sense that there be plenty of room for individuality. In the U.S. we have approximately 175 firefly species, some 36 of which are found in Texas. I’m guessing most of you remember capturing these harmless little bugs in a jar as a kid. Well, hang on, they’re not all as harmless as you think. I’m going to try to shake a few skeletons out of an unsuspected closet for you! We’ll also examine why they flash, how they flash, their life cycle, and how they protect themselves. We’ll even cover—for the bug nerds—how to identify some Texas fireflies at night.
There are three main flashing genera of fireflies (family: Lampyridae) in North America: Pyractomena, Photuris, and Photinus. We commonly find the second two in Texas. Photuris fireflies can be up to a full inch in length with long, slender legs. They have the appearance of being hunched around their shoulders and have diagonal stripes running down their wing covers. Their flashes are noticeably greener and brighter compared to the Photinus variety. Photinus fireflies are smaller (about a half inch), produce a yellow-green flash, and are the most prevalent in Texas (five species). We’ll look at the differences in these five a little later.
Fireflies, like butterflies, are fleeting symbols of nature’s beauty, living out only the last months of their life above ground. They don’t start out beautiful or agreeable. Females lay their eggs in the ground. Many larvae hibernate underground over the winter, others find places on or under the bark of trees. All fireflies have glowing larval stages, and sometimes, even the eggs glow—like some radioactive life force. Larvae emerge as voracious armored grub-like hunter-killers, right out of a cheap science fiction thriller. These hideous marauders are (snail eaters-medium)carnivores, and they terrorize earthworms, slugs and snails by first injecting them with a numbing fluid before devouring them. Adult fireflies can feed on nectar or pollen, or eat nothing at all (just mate, lay eggs, and die). As we will see later, some adults continue to harbor a dark and deceitful blood lust.
The bioluminescence of fireflies is an alchemist’s dream. The flash is controlled through special cells (photocytes), richly supplied by air tubes (tracheae), which also supply the insect with needed oxygen (no lungs). The flashing occurs when two chemicals, luciferin and luciferase, react with one another when exposed to oxygen in the presence of a substance known as ATP (every animal has ATP in its cells). By regulating the flow of oxygen into its abdomen, a firefly can turn its taillight on or off. This natural light, unlike manmade light, produces no heat and allows fireflies to share a beautiful language together.
And it’s a language of romance. When females are sufficiently attractive to draw a male and get inseminated—nature has done its job. The usual courtship goes something like this. While female fireflies lounge on a bush or blade of grass, the males fly around flashing a specific pattern, hoping for a female reply. Each flash is unique as to sex and species. When the female likes what she sees, she responds with a flash of her own—the brighter the response, the more interested she is. They continue this twinkling “conversation” until the male locates his partner and they mate. The flashes differ in color, intensity, duration and frequency, depending on species. Some even synchronize their flashes, choreographing a light show that ripples through the forest like a giant wave at the Super Bowl. Every year people flock to see the synchronizing Photinus carolinus in Great Smokey Mountains National Park and Allegheny National Forest in Pennsylvania (https://www.youtube.com/watch?v=sC2OkCEdqU4 ).
When attacked, fireflies shed little droplets of blood in something called “reflex bleeding.” The blood contains chemicals that taste bitter and can be poisonous to some animals. Consequently, they get marked off the menu by most predators. Scientists believe that firefly flashing may also serve as a defense mechanism warning of the insect’s unappetizing taste. The fact that even larvae are luminescent lends support to this theory. As mentioned, some species don’t flash at all as adults. These “dark” fireflies find each other through pheromones. Love always finds a way.
There’s an evil side to the flashing of the photuris species. Cannibalistic and gifted in the art of deception, the females of this species are right out of the movie Fatal Attraction. By mimicking the flash patterns of other species, photuris ladies of the night lure males to their bedroom only to be eaten. Aside from the fact that everybody must eat, preying on these horney dupes allows the ladies to acquire the toxins which are needed to deposit into their eggs as a chemical defense (they have none of their own). Predatory femme fatales have even been caught stealing wrapped fireflies from spider webs! How they identify the right corpse and emerge from the web unscathed remain unanswered questions. Wickedness is in the DNA of photuris males too—both sexes are bad to the bone. As deceitful as a damaged condom, sometimes photuris males imitate male photinus flashing in order to force themselves on an unsuspecting photinus female. It’s a jungle out there!
So, what about those five photinus species common to Texas? Nerds can research more deeply:
Photinus Texanus. Despite the reference to our own state, I couldn’t find very much on this one. They are common from West to Central Texas and the male’s flash interval in 2.9 seconds while hovering in place.
Photinus Stellaris. An erratic, reactive flasher (as flashing picks up from other fireflies), looks like little bolts of amber lightning streaking over the tops of bushes. Often found perched on a branch flashing single 1 second interval flashes. Flies early in the evening and only settles into a perched position later in the night.
Photinus Dismissus. Flashes every second with a bright, twinkling effect. Starts low to the ground, flies fast, and later moves higher to treetop level. Usually comes out a half-hour after dusk. Prefers consistently muddy creeks in partially wooded areas in Texas Hill Country.
Photinus Concisus. Flashes at 2 second intervals, comes out about 15 minutes after sunset and lasts approximately 20 minutes before diminishing. This one likes oak hillsides, riparian corridors and suburban lawns. Typical in Central Texas.
Photinus Pyralis. This is the most common firefly in North America. Flying in a J-shaped trajectory, they flash on the upswing. They come out around twilight and stay close to the ground. This species doesn’t eat at all. Males are common targets of the carnivorous photuris females described above.
Aside from the aesthetic, what use are fireflies? Remember the chemical ATP? All animal cells, including ours, have ATP in more or less constant amounts—or it should be. In diseased cells, the amount of ATP may be abnormal. By injecting chemicals from fireflies into diseased cells, important changes can be used to study many diseases from cancer to muscular dystrophy. The two chemicals critical to producing firefly light, luciferase and luciferin, are primarily used in food safety testing, but are helpful in another biomedical research too. Fortunately, these two chemicals can now be produced synthetically, without having to harm our little glittering friends. But that’s not all. Electronic detectors built with these chemicals have also been fitted into spacecraft to detect life in outer space. What have you done for mankind lately?
After all is said, for me fireflies represent freedom. Buoyant, transitory and beautiful. They enrich human existence and give each encounter the quality of a festival. With fewer encounters there are signs my grandkids may not grow up with the same firefly memories I have. It’s getting tougher for fireflies to survive. As forests and woodlands are cleared and replaced with concrete parking lots, shopping malls, and housing developments, room for them to live is becoming scarce. What natural habitat is left makes it difficult for the little flashers to find mates and reproduce because of pervasive light pollution. Oh well. . .things change. The good news is that memories don’t.
By Larry Gfeller