Summer Night Lights was originally published in the BFEC newsletter, Vol. 14/ No. 3, Summer 2010.
Even if you are unaccustomed to getting within 10 feet of an insect, you may be able to admire the (distant) sparkle of fireflies at dusk, a seminal summer icon. They add ambiance to a time of reprieve, when people emerge from air-conditioned houses to languid evenings.
Fireflies, also known as lightning bugs, are insects in the Lampyridae family, literally meaning “shining fire.” Their light, however, is “cool.” No heat is produced as a wasted byproduct, which helps explain its astounding 100 percent efficiency. Compare that to the 10 percent efficiency of an incandescent light bulb, which is usually hot to the touch.
Like most insects, fireflies have six legs and two pairs of wings. They are not “flies,” however, but rather beetles, with hard upper wings that fold over lower flight wings while at rest.
Every content but Antarctica is inhabited by fireflies, which number about 2,000 species, although there may be twice as many yet to be discovered. They generally thrive in warm, humid environments near water, and are most numerous in tropical Asia and Central and South America.
Some species live in dry climates and become active after rains. About 140 species can be found in North America, but curiously, they are nearly absent in the U.S. west of Kansas.
Even at the beginning of life as tiny eggs, fireflies can light up. The ability continues when they hatch into ground-dwelling larvae, sometimes referred to as “glow worms.” But not all adult fireflies can bioluminesce, and some biologists believe that the ability first evolved as a larval defense mechanism to warn off predators. As the theory goes, these flashes have since become a way for adults to find mates, making fireflies rare among insects in using sight instead of smell for sexual selection.
In the Midwest, firefly larvae can usually by found in tall grass or the decaying leaves of the forest floor. They also prefer to be near some form of water, or even ditches with moist soil.
Larva are carnivorous, sometimes eating prey (like earthworms) that are many times larger than themselves. After pupating in underground mud chambers, the adults emerge and live for only a week or two; some will not eat, rather spending all of their time and energy looking for a mate.
Adult females typically remain on the ground or perched on vegetation, and in some species are wingless. Males fly above and emit a series of flashes, looking for females of their own species to return the signal. Among species, light patterns vary in color, duration, intensity, pattern, and distance travelled between flashes.
Some tropical fireflies, particularly in Southeast Asia, truly light up the night by flashing in unison. In Malaysia they once lit the way for fishermen (though they may no longer, see below). There are also locations in the U.S. where this happens, notably near Elkmont, Tennessee (in the Great Smoky Mountains) and Congaree National Park in South Carolina.
Though the eating habits of many adult fireflies are unknown, and some are thought to not eat at all, those of the genus Photuris are based on mimicry.
Female Photuris fireflies mimic the flash patterns of females in the genus Photinus, thus luring Photinus males close and then eating them.
But the female Photuris does not get the last laugh; males of her own species mimic male Photinus, her prey. As the male Photuris approaches, she thinks she is catching a meal, but he is catching a mate. Catch all that?
Though not a great deal of data exists, firefly populations may be on the decline. Some evidence is anecdotal but convincing: tourist sites in southeast Asia have been deserted because the synchronous firefly show is all but gone.
The reasons for the decline are unclear, though there are several possibilities. The first is widespread use of pesticides, to which lightning bugs are vulnerable because they spend much of their time on the ground, and because they are predatory and accumulate toxins from their prey.
Another likely cause is light pollution — lightning bugs need darkness to see a potential mate’s light signals. Lastly, loss of natural habitat where fireflies live may be to blame. Luckily, there are ways to support this insect while inviting their light show to your yard:
Visit www.firefly.org to learn more about fireflies.