The Fizz on Fireflies
In the pantheon of summer pleasures, fireflies are right up there with watermelon, corn on the cob, a full sail on a broad reach, and a dive off the dock into a clear, glassy lake. An evening performance of dancing fireflies may be the closest we get, as mortals, to playing among the stars.
Some Background
Also known as lightning bugs, fireflies are actually a kind of beetle. There are 2200 species worldwide, and 165 or so in North America. The mid-Atlantic and southeastern states have the greatest abundance and diversity, but they can also be found here and there west of the Rockies.
The firefly life cycle includes four distinct stages: egg, larva, pupa and adult. Eggs get laid near ponds, streams, marshes, rivers and lakes, or in otherwise moist spots found in soil, moss or leaf litter. The larvae thrive in rotting wood and leaf litter and are voracious predators of snails, slugs and worms. I confess to harboring an image of fireflies as delicate invertebrate wood fairies, so this next bit of info caused some dissonance: the larvae inject their prey with a neurotoxin to paralyze it, then secrete digestive enzymes to liquefy it before gobbling (slurping?) it up. Slug smoothie, anyone?
They spend the next stage, as pupae, underground, in rotting logs, or in the furrows of tree bark. Adults typically emerge in late spring or early summer. In this phase, they focus all their energy on reproduction. They last just long enough to mate and lay eggs, about two weeks.
Shedding Light
It’s of course the bioluminescence that makes fireflies so astonishing. While the ability to create light is apparently somewhat common among sea creatures, it’s rare here on land. Entomologists believe bioluminescence first evolved as a way for fireflies to warn predators, as in, “Move along, nothing to see here but us bitter-tasting, crunchy-coated beetles!” Once they got good at glowing and flashing, though, they put those skills to use in other arenas, such as attracting mates.
It turns out that all firefly larvae are bioluminescent, but only some carry the trait into adulthood. There are in fact three types of fireflies, distinguished by their adult luminescence. Daytime dark ones are diurnal and unlit. Glow-worm types have flightless females who can shine for extended periods. Flashing species, the ones we know and love, produce quick, bright flares in the evening – with each species having its own distinctive pattern. These are more common east of the Mississippi, while the daytime-dark and glow-worm types dominate in the West.
Among the “flashers,” each species has its own distinctive sparkle pattern, color and timing. For example, the big dipper firefly (Photinus pyralis) performs in a J-shaped pattern that looks like…well, the Big Dipper. Also, both males and females light up as part of the mating ritual. The male flies around showing off his shimmer, while the female observes from a perch below. When a particular performance catches her fancy, she’ll swipe right by shining back.
Apparently there are a handful of species – Photinus carolinus among them – that perform synchronous displays, meaning the males coordinate to glow in unison. The original flashdance! Guess I’m not the only one who thinks this would be a treat to see in person. Every year, tens of thousands of “firefly tourists” descend on sites in Tennessee, Pennsylvania and South Carolina to observe the phenomenon.
Sadly, firefly populations are declining. Scientists are scrambling to figure out the scope of the problem. Meanwhile, they’ve identified a dozen or more species – of those they’ve studied – that are at risk of extinction. One of the most endangered is the Bethany Beach firefly (Photuris bethaniensis), which is native to a 20-mile stretch along Delaware’s southern coast. The species thrives only in the freshwater wetlands that form in low spots between sand dunes. Development is overtaking these spots. The main threats to fireflies globally are loss of habitat, pesticide use and light pollution.
What Can I Do?
Protect prime egg-laying spots such as wetlands, streams, ponds, marshes and wet fields.
Leave leaf litter and old logs in your yard and minimize soil disturbances, such as tilling, to provide and protect habitat for larvae and pupae.
Replace some of that turfgrass lawn with native plants that will provide shelter and mating opportunities for adult fireflies, while supporting a broader food web.
Avoid using pesticides, especially neonicotinoids and insecticides targeting adult mosquitoes. Neonicotinoids are broad-spectrum pesticides often found in lawn chemicals. They linger in the environment, harming larvae and their prey. Mosquito sprays will harm fireflies as collateral damage.
Minimize light pollution from outdoor lamps by turning them off, dimming them or replacing them with motion-sensor or yellow “bug light” bulbs. The survival of many firefly species depends on them detecting one another’s flashes in the dark and warning off predators. Artificial light makes flashes less visible to friend and foe alike.
Should you need more inspiration, Old Blue Eyes would surely testify that nothing’s more romantic than a field of stars.
Many thanks to Radim Schrieber of Firefly Experience for permission to share some of his awe-inspiring photographs with you.
Resources
Doreen Cubie, “Nixing Neonics to Protect Pollinators,” The National Wildlife Federation, January 30, 2018.
Adrian Higgins, “Humans Love Fireflies, But We Haven’t Made Life Easy for Them,” The Washington Post, July 6, 2016.
Sara Lewis, “Silent Sparks,” The National Wildlife Federation, April 1, 2022.
Craig Mattson, “The Illustrious Life of the Firefly,” Schlitz Audubon Nature Center, June 21, 2021.
“Firefly Species at Risk,” Xerces Society.