Security Lights Threaten Fireflies

As a kid, many a June twilight was spent trailing the beacons of fireflies in the deepening dusk to try and catch them in my hands. I was endlessly enthralled. Endlessly until Mom called to clean up for bed, at least. It pleases me that my own two children went through this phase, presenting me with Mason jars of flashing green magic before they released “their” fireflies outdoors.

For the longest time, I remained enchanted by those shimmering, summer-night faerie lights. These days I’m charmed only by the memory of such. They’re nearly gone from our farm now, a paltry few flashing in a meadow that once hosted a Milky Way of moving lights.

With 2,000 known species, fireflies are native to both the Americas and Eurasia. In the larval stage, they’re carnivorous, and eat many insects we consider pests. You may see young fireflies, grub-like “glowworms,” in the lawn or flower bed. Larvae also feed on worms, slugs and snails before wriggling down into the soil or other protected space to overwinter. After a short pupal stage, they emerge to mate. Adults mainly subsist on pollen and nectar, though a few don’t eat at all in their brief grown-up phase.

Among the reasons fireflies have been well-studied is that they produce the most efficient light in the world, with 100% of the energy in the chemical reaction used for illumination. When the enzyme luciferase hits luciferin in the presence of magnesium, oxygen, and ATP, it results in light devoid of any heat (that comes later when they find a mate).

Flash patterns and colors vary from one species to another, and among the sexes. It is more common for females to stay put and send out their Morse code while the guys work up the nerve to approach a mate.

Occasionally, flashes among disparate sexes and species will synchronize temporarily, something for which there is no explanation as yet, other than to flummox biologists. I have to say it’s “pretty cool,” technically speaking. The most common color of light is yellow, although it can be green, or even red, depending on species. In certain light conditions, some shades of green can be perceived as blue.

Although the orgy of glitzy flashes in late spring and early summer is mainly to signal for a hookup, there are other reasons fireflies light up their butts. Both larvae and adults contain a bitter toxin which is closely related to the stuff toads make. Just as nothing eats toads – or at least not twice – due to their toxicity, predators don’t knowingly eat fireflies.

It is believed that juvenile light-shows are to advertise that they’re unpleasant to eat, thus avoiding predation. Biologists call overt markers such as this and the bright colors of poisonous frogs “honest signals.” At least one type of cannibalistic firefly mimics the flash pattern of another species, luring those males in with the promise of sex only to eat them. I’m guessing this would be a “dishonest signal.”

Fireflies’ light-emitting chemicals are used in medicine to detect blood clots, tuberculosis, diabetes, and some cancers. For most applications the chemicals are now synthesized, but a small percentage is still harvested from fireflies, a practice which must soon be halted.

I highly recommend the superb and heartbreaking 1988 Anime film Grave of the Fireflies, which is based on a true story. For the younger of the two child-protagonists, fireflies bring joy. Her older brother, though, sees in fireflies the souls of the war-dead rising to heaven, as well as the daily barrage of firebombs which has left them homeless orphans.

While not as poignant as children suffering the effects of war, the story of today’s fireflies is sad nonetheless. The eerily glowing beetles are at risk worldwide, and according to entomologists, many firefly species may soon be extinguished altogether.

A year-long Tuft University study, published in February 2000 in the journal BioScience, surveyed firefly populations in North America, Central America, Europe, South Asia, East Asia, and Southeast Asia. It found that in every region, fireflies are in trouble.

But it’s not only fireflies. Insect populations are in freefall everywhere: Between 1996 and 2016, Ohio lost a third of its butterfly population. German scientists have documented a 75% drop in the number of flying insects in nature preserves in just the past 27 years. Not surprisingly, this has contributed to the loss of insect-eating songbirds. The causes of this alarming insect decline are complex, but pesticide use, climate change, and habitat loss are driving this die-off to a large extent.

Where fireflies are concerned, though, it turns out that exterior lighting is the second-most important factor in their decline, right after habitat loss. Most of us can’t individually make a dent in global warming, put a stop to urban sprawl, or curb the use of agricultural chemicals in the next 24 hours. But we can, literally, help fireflies overnight – by turning off exterior lights. Motion-triggered security lights can replace floodlights that run constantly. We can use lower wattage bulbs, and do away with outdoor lights which are used for aesthetic purposes only.

Being mindful of how we illuminate the outdoors is a small bother compared to losing fireflies. Perhaps if we can work to reduce light pollution in our communities, we’ll one day see thousands of shimmering Tinkerbells on summer evenings again. Maybe our kids and grandkids will have the privilege of catching magic in Mason jars, and watching the procession of lights heavenward when they let the fireflies go.

For more information, see the report “A Global Perspective on Firefly Extinction Threats.”

Photo of firefly courtesy Wikimedia user Bruce Marlin.