Nothing says summer has arrived like the twinkle of fireflies.  

As the weather starts to warm, I keep an eye on the woods as the sun sets, searching for that neon glow.  I have fond memories of chasing fireflies as a child, and something about them still seems magical to me.

I was absolutely thrilled to move from a place where the fireflies had seemed to have disappeared (more on that later) to somewhere where they grace the landscape every summer evening.

What Are Fireflies?

A firefly resting on a leaf.  Its light-producing lantern can be seen.

Despite their name, they aren’t actually flies at all: they’re beetles.  

Like other beetles, they undergo metamorphosis as they progress through the four stages of their life cycle:  egg, larva, pupa, and beetle—all of which may be capable of glowing.

Where Are They Found?

Fireflies are found on every continent but Antarctica.

There are about 2000 different species worldwide, with more than 170 species found in North America alone.  

In general, they prefer warm, humid areas. Because they need a moist environment to survive, they can be found in forests and fields, especially near lakes, rivers, ponds, and streams.  

Why Do Fireflies Flash?

Fireflies flashing at dusk

The primary reason for the flash is to attract a mate.  It is typically the male of a species that flies through the air, flashing a species-specific pattern.  Females watch the males’ displays, and when they see a suitable pattern, they respond with a flash of their own.  

Other carnivorous fireflies, nicknamed “femme fatales”, attract males by mimicking the flash of receptive females.  When males arrive to mate, they are eaten instead.

The flash is also thought to discourage predators.  Their blood contains chemicals with a bitter taste. Predators learn to associate the familiar flash with an unpleasant taste and steer clear of the insects.

How Do They Flash?

Each firefly has a specialized organ, the lantern, dedicated to producing light in a process known as bioluminescence. Special cells called photocytes line the lantern, and it is within these cells that the chemical reactions necessary to produce light occur.  Light is produced when the enzyme luciferase and the compound luciferin react in the presence of energy (ATP) and oxygen. Current models suggest that the insect controls its flash patterns by controlling oxygen levels in its lantern.

The light produced in a flash is remarkably efficient.  While a standard incandescent light bulb loses 90% of its energy as heat, firefly light is considered “cold light” since 100% of the energy produced is emitted as light.

What Happens to Them During the Winter?

Adults live chiefly to mate and produce eggs and only live 3-4 weeks.  At the end of summer, females lay approximately 100 eggs in the soil before dying. Worm-like larvae hatch throughout the fall and are carnivorous, feasting on small insects, snails, and slugs.The larvae spend the cold winter below ground,  In late spring, adults emerge from pupa and the cycle repeats again.

Are Fireflies Disappearing?

Yes, fireflies are disappearing, and several factors are to blame.

Studies have shown that human light pollution disrupts light patterns.  Lights from houses, cars, buildings, and street lights make it difficult for fireflies to signal to one another during mating season.  As mating decreases, so too does the number of offspring produced each season.

Additionally, as more land is developed for housing and industry, fewer regions hospitable remain.  Because fireflies and mosquitoes share the same affinity for warm, moist regions, they frequently inhabit the same areas. Unfortunately, pesticides used to control mosquitoes also kill fireflies.  When I was a child in Florida, firefly shows were a nightly occurrence each summer. When the county began regular pesticide spraying to control mosquitoes, the fireflies disappeared as well. Coincidence? Perhaps, but I doubt it.

Steps You Can Take to Protect These Fascinating Creatures

  • Avoid using pesticides, especially on your lawn.  
  • Limit the number of outdoor lights you leave on during the summer months.
  • If you (or your children) catch fireflies in a jar to observe them more closely, be sure to release them.
  • Consider letting a part of your yard stay “wild”.  Let the grass grow a little longer to give the fireflies a safe place to spend their days.  Likewise, avoid raking leaves in the fall so that the young have a protective cover in which to spend the winter.  

Fireflies are a beautiful, magical, and amazing part of summer. Let’s do our part to ensure they stick around.

Further Information

Learn all you’d ever want to know at Firefly.org.

Firefly Fact Sheet

10 Fascinating Facts About Fireflies

How These Mysterious Fireflies Synchronize Their Dazzling Light Shows

Firefly Life Cycle

How and Why do Fireflies Light Up?

Why do Fireflies Glow?

Molecule of the Month: Luciferase

Have you spotted fireflies yet this season? Fireflies (or lightning bugs) have always brought out the kid in me. The science behind their glow is fascinating, and has actually puzzled scientists for more than 60 years. What are fireflies? Where are they found? Why and how do they flash? What happens to them over the winter? Are fireflies disappearing? What can be done to protect fireflies?


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