Nature Notes: Those Flashy Fireflies
You may have noticed that most of the songbirds have stopped singing and are either preparing to nest again or, more likely, just help their fledglings along while simultaneously nudging them away. Young-of-the-year ospreys have either already fledged or are standing in their nests flapping their wings in earnest as they anticipate the moment of departure.
While the birdcalls wane, the insects take the stage with their sounds, flights, pheromone secretions, and even lights. On Saturday, the 21st anniversary of the TWA crash into the ocean off Fire Island, the snowy tree crickets began to utter their trills in warm-up sessions in the early evening. It’s early in the season, but ironically, perhaps, on the evening of that tragic air crash they also began to sing. On Sunday morning they were so eager to get going that they sang while the sun shone brightly, a bit out of fashion for the nocturnal chorusers they are. On Monday evening they were in full form. In most years tree crickets and katydids don’t begin their nightly singing until the end of July or beginning of August.
The humid hot spell that started on Saturday may have been the catalyst. On Sunday evening it was both hotter and more humid. A perfect time for fireflies to come out in force, and out in force they came. I went with my grandson, Matthew, from San Francisco, where they don’t have fireflies, to census them on the South Fork, starting in eastern Southampton and ending up in East Hampton.
The moon hadn’t reached the first quarter and the skies were mostly clouded over — perfect, for the little lights these flying insects in the beetle group put out. Starting in Sag Harbor and ending up in Noyac, we counted 194 different flashing fireflies as we cruised at about 30 miles per hour along the Bridgehampton-Sag Harbor Turnpike, Brick Kiln, Old Sag Harbor, Millstone, Scuttlehole, Sagg, and Town Line Roads, and Parsonage Lane before entering East Hampton. Wainscott Northwest and Daniel’s Hole Roads came next. It was 8:35 and Matthew was still counting fireflies and writing them down in the dusky light.
Then, something odd befell us. After we reached Route 114 and it was almost dark, we didn’t see any fireflies. We recorded not a single flash on Whooping Hollow Road, Stephen Hand’s Path, Two Holes of Water Road, Bull Path, Old Northwest Road, and Swamp Road.
Matthew, who will be a high school senior next year and is contemplating a scientific education thereafter, came up with an interesting hypothesis: Maybe the male fireflies only flash at dusk, when they can still make out their potential mates flashing in the groundcover below. After that, if they flash they might be subject to increased predation from crepuscular fliers such as whippoorwills and bats.
In all we traveled 35 miles. From 7:45 to 8:50, we counted 194 fireflies along 8.5 miles of roads for an average of 22.82 fireflies per mile. They were more common to the south — say, along Scuttlehole Road in Bridgehampton and Parsonage Road in Sagaponack — than to the north. It was encouraging to find so many at a time when honeybees, butterflies, fireflies, and other insect populations have become noticeably low.
The firefly, or lightning bug, that we were studying is the Pennsylvania firefly, Photuris pennsylvanica, the most common and widespread member of the family Lampyridae. Some fireflies don’t emit light pulses, but use pheremones to attract mates. There are fireflies all over the world, but they are rare west of the Rocky Mountains in the United States. In parts of Indonesia and Southeast Asia, hundreds of fireflies flash simultaneously, lighting up the trees they’re perched in, creating quite a spectacle. Similar firefly flashes in unison are recorded regularly in parts of Tennessee in the Great Smokey Mountains and in South Carolina. People congregate in such areas in early June on an annual basis to take in the show.
While I was in the Army and stationed in Japan, I visited a park in Tokyo where the annual firefly exhibition receives a great number of observers, both parents and children, not unlike the way we in America turn out for the annual July fireworks shows. The glow emitted by the light organ at the end of the firefly abdomen is called “cold” light and is one of the most efficient lights in terms of cost in energy. With incandescent light from a lightbulb 10 percent of the energy is used as light, 90 percent as heat. Florescent lights use 90 percent for light, only 10 goes off as heat. The fireflies’ glow produces no heat; 100 percent of the luciferin-luciferase reaction behind each pulse is emitted as light.
The larvae hatch from eggs laid in damp spots or rotting wood by the female and take a year or more to mature. Both the eggs and the larvae are luminescent. Interestingly, the larvae feed on snails, slugs, worms, and other small organisms that live in and on the leaf litter and grassy swards. If you have slugs that devour flowers and certain leafy vegetables, be kind to the fireflies in your yard!
By the same token, the larvae are not very palatable, as they contain certain distasteful toxins. Considering all of its developmental stages, this little beetle that we take for granted sports a sizeable dossier of anti-predator strategies and is certainly one of the most advanced of the millions of insect species throughout the world. Perhaps that is why there are more than 2,000 firefly species. Not all of them are capable of producing light, but they have other weapons in their arsenal to keep them going.
Ironically, however, there is a predator firefly that flashes to a male firefly seeking a mate in the same species-specific code, a “hacker” of sorts. It pretends it’s a female of the same species and lures the male, then attacks it and eats it. Not unlike the praying mantis, it’s a real femme fatale!