Summer Night Fairy Lights
Here come the real stars to fill the upper skies, and here on earth come emulating flies, that though they never equal stars in size, (and they were never really stars at heart) achieve at times a very star-like start. Only, of course, they can’t sustain the part.
Fireflies in the garden, by robert frost
The first blinks of light appear in the recesses of the backyard just as twilight casts its spell and songbirds sing their final notes of the day. The lights slowly increase in number, a constantly shifting pattern of flashes that continues endlessly and intensifies as darkness deepens. Anyone who has grown up in the eastern part of the United States likely has fond memories of chasing and capturing fireflies on summer evenings. They conjure up multi-sensory images of soft cool grass under bare feet, buzzing cicadas, porch lights, and the inevitable call to come in the house and hop in the bathtub. Many a child has drifted off to sleep with captured fireflies casting a dim light from inside a jar next to their bed (hopefully to be released the next morning). Their ‘friendly’ reputation makes them ideal for encouraging children to feel comfortable with insects. Indeed, they are one of the few insects that people don’t intentionally kill.
Fireflies, or lightning bugs to some, are that rare experience of childhood that retains some of its undimmed magic for us even as we grow up. If they were a phenomenon to be seen in only a specific remote locale or one night of the year, people would book expensive vacations to see them. The first firefly of the season is a natural milestone that occurs by the middle of June during most years here in the upper Midwest. By the 4th of July, the apex of the summer evening entertainment schedule for many people, the light show can be downright jaw-dropping in good firefly habitat – an entirely soundless alternative to the booming and crackling fireworks displays that bring out the crowds. Fireflies, of course don’t require a celebration of national independence or even a human audience, for that matter, and their fireworks will continue nightly for several weeks.
Fireflies/lightning bugs are neither flies nor bugs, but are beetles, an entomological distinction that probably matters little to most people. Nonetheless, beetles they are, as evidenced by their leathery wing covers, and thin translucent underwings, which are used for flying. All fireflies are members of the Lampyridae insect family. There are over 2000 species throughout the world, with over 200 in North America alone. They are primarily insects of forests, grasslands or wetland habitats, the larvae spending up to a full year of their life in the soil. In the U.S., most firefly diversity is found east of the Rocky Mountains. Nearly all are able to produce light, known as bioluminescence. Most are nocturnal, but some diurnal species active during daylight do not produce light. Many of the common varieties in our area look very much alike, differing mainly in size and other minute details. The easiest (and most enjoyable) way to tell them apart is to learn to distinguish the different patterns of flashes emitted by the males as they seek to attract females. This, after all is the romantic reason behind the flashes of light that make summer evenings so magical.
The manner in which fireflies produce their lovely flashes of bioluminescence is a fascinating bit of chemistry. The enzyme luciferase acts on another compound, luciferin in the presence of oxygen to produce light. This light is over 95% efficient, meaning that close to 100% of the energy expended is actually emitted as visible light waves. Contrast this to an old-fashioned incandescent light bulb, which converts only 10% of total energy into visible light, the rest being emitted as heat. The ability to produce this ‘cool’ light so efficiently intrigued scientists for many years as they searched for more efficient ways of producing light for human uses. Modern LED bulbs achieve about 40-50% efficiency. Next generation LEDs being developed are purported to get closer to 90% efficiency by mimicking the reflective scales that fireflies possess. The light emitting organs are located on the rear segments of the insect’s abdomen. Fireflies are able to turn their light-producing organs on and off, producing very specific patterns of flashes that are recognized by others of their species.
Bioluminescence as a natural phenomenon may seem incredible to us; however, it is actually very common in the world’s oceans. A majority of deep-sea fishes possess the ability to produce their own light and many species of tiny phytoplankton are able to light up tropical beaches. Fireflies are one of the few examples of bioluminescence in land-dwelling creatures. Although firefly diversity is high in warmer climates, Illinois is host to 26 species, and the Chicago area sees just a handful of those. While not found in Illinois, the synchronous firefly, Photinus carolinus, is able to synchronize their flashing so that all of the males are flashing in ‘chorus.’ It is this amazing spectacle that draws thousands of visitors to the Smoky Mountains each year in early June. This event has become so popular that the National Park Service holds a lottery each year for the vehicle passes required to attend.
In general, the fireflies that flash while flying are males while stationary insects near the ground or on low vegetation are female. When females recognize the appropriate flash pattern from a male of the same species, they will, after a specifically timed pause, return their own distinct flash, signaling to the male that they are available for mating. The male responds by alighting near the female, where mating takes place. A very common variety in the eastern U.S. is the Eastern Firefly, Photinus pyralis, and easily identified by the lazy “J-shaped” flashes made by the flying males every 4-5 seconds. The horizontal ‘swoosh’ which defines this firefly’s distinctive flash pattern gives it the name Big Dipper. Other varieties fly in either straight lines or meandering lines, or fly close to the ground while others can be seen navigating the tree canopy. Some display a regular series of flashes followed by a pause, while others a regular cadence of flashes. Some emit a greenish light while others emit an amber colored flash that fades like an ember. What becomes apparent to the patient observer is the fact that, in fireflies, nature has devised a sort of visual Morse code. In this case, a specific coded message is assigned to each species, all of which translate to the same romantic invitation.
Sometimes, though, the message is one of deception. Several species, notably those belonging to the genus Photuris, prey on other fireflies. The female Photuris fireflies are able to mimic the flash patterns of other species. When the male flies in, intending to mate, he is instead pounced upon and eaten. While most non-predatory adult fireflies do not eat at all during the 7-14 days they spend as adults, they are all predatory as larvae, feeding on snails, slugs, earthworms and other small creatures to be found under logs and in the leaf litter. As larvae, fireflies are sometimes called glow-worms, since the larvae also possess light-producing organs. Even firefly eggs have been found to glow when stimulated by vibration.
This hallmark of summer evenings doesn’t occur in as many locales as it once did due to changing land-use and landscaping practices. Fireflies need adequate leaf litter, moist soil, darkness, and protection from pesticides to thrive. While droughts and warmer winters brought on by climate change are also affecting their numbers, most species of fireflies are adapted to variable climate – to a degree. Some species, with very specific habitat requirements, are now threatened with extinction. Even the more common species, such as the eastern firefly, the one with the lazy-J flash, are not found in areas where their habitat has been mostly replaced with manicured lawns and illuminated by overhead security lighting.
Similar to many of the sustainable landscaping practices I advocate to provide habitat for local birds, butterflies, bees, etc., fireflies can benefit from the following things:
- Reduce or eliminate pesticide use on your property.
- Maintain naturalized areas with taller, diverse native plants and where leaf litter and old logs can remain to decompose naturally. Low-lying areas that hold water and remain damp for a few days after a rain are especially valuable as naturalized ‘rain gardens.’
- Reduce the amount of lighting on your property by restricting it to downward-projecting patio lights, and put security lights on motion sensors or timers.
- Encourage local public agencies (villages, park districts, etc.) to convert some of their lands to naturalized plantings and support them in these decisions.
As summer’s magical glow fades in the August heat, the fireflies’ fairy lights will have faded as well for another year, appearing in our memory like a mid-summer night’s dream. More than almost anything else, fireflies have the ability to remind us that nature possesses a sublime beauty and mystery that is undiminished by scientific understanding. Although a child would never put it quite that way, most would agree that fireflies are beautiful, mysterious, magical, and pretty cool.
