As a kid, I remember the magic of seeing clouds of fireflies on a warm summer night. Nowadays, I get excited if I see one or two floating around our yard. Also called lightning bugs, these special little insects are an important indicator of environmental health. And they’re also good for our gardens. So, how does a gardener support them? What do lightning bugs eat? What’s the difference between lightning bugs and fireflies? What about glow-worms? (Are those even a thing?!) It’s easy to find confusing or conflicting information about these bioluminescent marvels online. In this article, I’m going to share some tips on what these special creatures need to survive, how we can help sustain them, and why we should make the effort.
Meet the lightning bug—a.k.a. the firefly
Earth has more than 2,000 species of fireflies in all. You’ll find them nearly everywhere—except for the Antarctic. Commonly known as lightning bugs or fireflies, these insects in the Lampyridae family use flashes of light as mating signals. Fireflies in the genus Photuris and those in Photinus are two common types.
Of course, there are many more kinds of fireflies ranging in size and featuring different flash colors and configurations. Despite their differences, they do have something in common—namely the mechanism behind their ability to light themselves up. It’s a little complicated, but here are the basics. Essentially, a chemical reaction takes place within specialized light organs within each insect’s abdomen. Among the chief chemicals involved is a molecule known as luciferin, an enzyme called luciferase, oxygen, and adenosine triphosphate (ATP). When combined, this complex stew creates the lightning bug’s signature glow.
Where can you find lightning bugs?
There are fireflies throughout Canada, the U.S., and much of the rest of the world, but firefly species and their concentrations do vary widely. For example, if you live in the eastern U.S. you are more likely to encounter overtly flashing lightning bugs—especially during the more humid months of June and July. However, western states are more likely to have less conspicuous or non-flashing species.
Fireflies’ life cycle
To answer the question what do lightning bugs eat, it helps to understand how their life cycles work. Every firefly starts out as a tiny egg. After a few weeks, eggs hatch and firefly larvae emerge. Depending on the firefly species and area conditions, larval stages can take one or two years to complete. In time, the larvae develop into pupae—the last stop before adulthood. Pupal fireflies can take anywhere from one week to three to finish developing wings and other essential parts. Once this transformation is complete, adult fireflies emerge and live for just three or four weeks in all.
It’s during that lengthy larval stage that fireflies do most of their eating. (Incidentally, parts of the wormlike larvae do glow. As a result, some people refer to larval stage fireflies as glow-worms.)
What do lightning bugs eat as larvae?
Larval stage lightning bugs prey on all sorts of soft-bodied insects, as well as worms, slugs, and snails, among other things. Some lightning bug species spend most of their larval stages burrowed beneath the soil. Many others stay just above ground, hidden amongst the leaf litter on the soil’s surface.
What do lightning bugs eat as adults?
And what do lightning bugs eat as adults? That’s a trickier question. Technically, most adult lightning bugs don’t have to eat. During this life stage, both male fireflies and females are focused on mating—not eating. Nevertheless, some adult lightning bug species have been observed taking in nectar from common milkweed plants.
Now for the tricky part. Lightning bugs from the Photuris genus—specifically Photuris females—are femme fatales. These female fireflies respond to the mating flashes of males from other lightning bug species. Once lured in, the males are attacked and eaten by the females. As a result, the successful female picks up protective chemicals, which she initially lacked, from her unlucky-in-love male meal. These chemicals help to make her and her future offspring toxic to many—but not all—would-be predators. (A select few birds, toads, and certain lizards, for instance, seem to be able to eat lightning bugs with no lasting ill effects.)
Why fireflies are great for the garden
So, what do lightning bugs eat? In all, it’s a respectable list of potential garden pests, including aphids, cutworms, cabbage worms, grubs, slugs, and many others. Recall that, during their rather lengthy larval stage, lightning bugs are voracious eaters. Primarily, they focus on soft-bodied insects, as well as slugs and snails.
Because some adult fireflies also have been known to interact with nectar and pollen, they may also contribute some pollination services. (To bring more lightning bugs and other beneficial insects to your garden, check out Jess’ book Attracting Beneficial Bugs to Your Garden.)
How to help protect lightning bugs
If you’re over the age of, say, 45, you might’ve noticed there aren’t as many fireflies around as there once were. As Fireflies, Glow-worms, and Lightning Bugs author Lynn Frierson Faust notes, “I have witnessed one after another distinct and impressive firefly population disappear due to road widening, to subdivision development, to high school lights that we can see from our farm over a mile away, to homeowners who burn floodlights all night long, to overzealous lawn warriors with their arsenals of poisons… [Multiple] factors have combined to make it harder for fireflies to live, thrive, and find a mate in today’s world.”
Want to help these beleaguered beetles? Here’s how:
- Forego pesticides: Pesticide use is a non-starter since larval lightning bugs spend a year or more in the soil before finally emerging as adult fireflies.
- Go dark: Reduce light pollution in the area by eliminating all superfluous nighttime lighting. (Adding blackout curtains inside your home also can help keep your indoor artificial lighting from leaking out into the night.)
- Make beetle habitats: Combat habitat loss by allowing some leaf litter to build up, planting a wider variety of native flowering plants, and building in some soggy patches where female fireflies can lay eggs.
- Let them fly: Keeping fireflies captive in a jar topped with a hole-punched lid may be tempting, but, these days, it’s best to admire fireflies from a distance.
- Become a citizen scientist: Whether you do (or don’t!) see fireflies in your area, report your observations to Firefly Atlas. The citizen science project collects data researchers can use to monitor different firefly species’ population numbers, changes in their geographic ranges, their reactions to climate change, and more.