What Do Fireflies Eat? | All About Fireflies

Think back to those warm summer nights you spent in New England when you were a child. If you were anything like me, you devoted at least a few of those evenings to chasing fireflies around your backyard, glass jar in hand. For a lot of people, the blinking lights of fireflies are just as much a part of the classic summer nighttime scene as the chirping of crickets, the calling of katydids, or the buzzing of mosquitoes (as much as we wish that last one wasn’t). Most of us have probably only crossed paths with fireflies during the evening hours, when our lives briefly overlap, but this means that the rest of a firefly’s life, despite it being among the most famous and well-liked insects, is largely shrouded in mystery. So when fireflies aren’t flying around and showing off their luminance, what are they doing? Where do they go during the day? What do fireflies eat? What do they even look like when they’re not a blinking yellow-green light?

Below, you’ll find the enlightening answers to all of these common firefly questions.

What Are Fireflies?

Fireflies (or “lightning bugs”) are a family of beetles known for their ability to produce light. Through the use of specialized organs in their abdomens, they’re able to set off chemical reactions that result in a blinking or glowing light. This process is commonly known as bioluminescence and can be found in anything from fish to fungi.

Some fireflies blink their lights on and off in fancy patterns, others just emit a steady glow, and some can’t do either of those things. In fact, despite their common name, many firefly species are unable to produce any light at all.

Why Do Fireflies Light Up?

The reason why only some fireflies light up all comes down to—like most things in life—attracting a mate. Some species of fireflies evolved to use blinking or glowing lights to find a breeding partner, while others evolved to use invisible chemical signals (pheromones) instead. For the light-up species, the male will fly around and blink his lights in a certain, species-specific pattern—like a love song in Morse code. He’s trying to catch the eye of a female firefly, who he hopes will blink her own light in response from somewhere nearby.

When most people encounter them, fireflies are fully-grown, flying beetles, but they begin life in quite a different state. They start out as eggs in the ground and then quickly grow into larvae (sometimes called glowworms), which can spend up to several years underground. In the spring, the larvae turn into pupae and, subsequently, adult beetles.

Unlike their mature counterparts, all firefly larvae have the ability to glow. However, the larvae’s glowing doesn’t serve the same purpose that it does in adults: in larvae, glowing is instead used as a warning for predators. Hungry animals that eat a firefly larva soon come to regret their meal—a special chemical found in most firefly blood gives off a very foul taste. Predators learn to associate this bad taste with the firefly’s luminance and next time look elsewhere for a quick bite to eat.

What Do Fireflies Eat?

In their larval stage, fireflies are carnivorous. They eat soft-bodied insects that live on or in the ground, like snails, slugs, worms, or other larvae.

As they mature and turn into beetles, they do one of several things, depending on which species of firefly they are. Some fireflies eat the nectar or pollen of flowers, others eat smaller fireflies, and some don’t eat anything at all. This is due to the adult firefly’s relatively short lifespan, which is typically no more than a few months long and is normally spent looking for a mate.

Fireflies of the genus Photuris are especially devious when it comes to feeding. Females will lure in males of other species by mimicking their blinking patterns, so the hapless males fly over to the females in hopes of procreation, but are instead greeted by predation. This behavior has earned these particular lightning bugs the nickname “femme fatale fireflies.”

Where Do Fireflies Go During the Day?

Although most fireflies come out only at night, many species are active exclusively during the day. These species spend the daylight hours breeding and eating, while their nocturnal counterparts rest in fields or wooded areas until after dusk. Due to the brightness of the sun during the day, most diurnal fireflies have abandoned the ability to glow and instead use pheromones to attract their mates.

How Common Are Fireflies?

If you feel like you’ve been seeing fewer and fewer fireflies over the years, you’re not alone. They were once a very common sight throughout New England, but today, they’re more difficult to find. It’s hard to say for sure what has caused this decrease in the firefly population, but experts theorize that it could be due to pesticide use, habitat loss, or light pollution.

Hopefully, your most pressing firefly questions have now been answered. With your new-found appreciation for these glowing insects, you may be interested in signing up for Mass Audubon’s Firefly Watch Citizen Science Project. The program allows you to report your own firefly sightings online, which helps scientists track firefly populations across New England and hopefully determine the cause of their troubling decline.

Did you ever wonder “What do fireflies eat?” or “Why do fireflies glow?” Let us know!

This post was first published in 2016 and has been updated. 

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