The flashes of fireflies on a warm summer night remind many of us of our carefree childhood sense of wonder. With firefly season almost upon us, their enchanting light displays will soon spark our curiosity and capture our imaginations.
Perhaps because we are so familiar with them, either from growing up chasing them or seeing them portrayed in art, film and books, we may think that we know all about these simple insects. Yet our flashy friends have a dark side that includes little-known tales of deception, poisoning and death. As summer approaches, here are 11 cool things about fireflies that you might not know.
Fireflies are beetles. Whether you call them fireflies or lightning bugs, these insects are neither flies nor true bugs. Instead they are beetles, just like ladybugs and rhinoceros beetles. Like other beetles, fireflies have a pair of hardened wing cases, called elytra, that the wings fold underneath. The elytra open for liftoff like gull-wing doors on a car, freeing the wings for flight.
There are more than 2,000 species of firefly worldwide. Fireflies are found all over the world, on every continent except Antarctica—and they are incredibly diverse. There can be many species sharing just one habitat. In fact, you are probably looking at multiple species when you are watching them in your own yard.
Flashes are the firefly language of love. Fireflies use flashes as mating signals. The flashes that you see in your yard are generally from males looking for females. They flash a specific pattern while they fly, hoping for a female reply. If a female waiting in the grass or bushes likes what she sees, she responds back with a flash of her own. They will engage in this twinkling “conversation” until the male locates the female and they mate. Each species has its own pattern—a code that lets individuals identify appropriate mates of the same species.
Not all fireflies flash. While all fireflies light up in their larval forms, there are many species of fireflies that do not use light as an adult mating signal. Instead, these “dark” fireflies use airborne smells, such as pheromones, to communicate.
Fireflies spend most of their life in the larval stage. While not all adults emit light, all fireflies have glowing larval stages. The armored, grub-like larvae are vicious predators, tracking down and consuming slugs, snails and earthworms. They can spend up to two years in this larval stage before metamorphosing into adults. Adults may live only a couple of weeks, and most do not eat during this time—they just mate, lay eggs and die. This means that the fireflies you see in your backyard this summer are the result of successful matings from 2017 and they will be the parents of fireflies that you will not see flashing until 2021.
Firefly femme fatales lure unsuspecting males of other species to their deaths. The females of one group of fireflies, called Photuris, have earned the nickname femme fatales. Unlike most species, these fireflies eat as adults. By mimicking the flash patterns of other firefly species, the female lures unsuspecting males in closer. Thus duped, a male will serve as the main entree for her dinner. Preying on the males of other species allows Photuris females to acquire their toxins, called lucibufagins, which the females then deposit into their eggs as a chemical defense.
Femme fatales sneak onto spider webs to steal prey. Predatory femme fatales have been caught stealing wrapped fireflies from spider’s webs, a behavior called kleptoparasitism. How they identify their incapacitated prey and emerge from the web unscathed remain unanswered questions.
The biggest fireflies are huge. Females of the Lamprigera firefly can grow to be the size of your palm. They are much larger than their male counterparts and lack wings. Two large light organs on their abdomen produce their characteristic glow.
There are winter fireflies. While fireflies are largely seen as a staple of summer, there is one North American species that is active in the winter. Adults of these winter fireflies do not emit light and hide in the bark of trees, so they largely go unnoticed. Emerging to find overwintering sites in September and huddling in the furrowed bark of large trees through the winter, they find each other with pheromone signals in April and May, mate, lay eggs and are gone before their summer counterparts arrive.
Some fireflies flash in unison. Some species of firefly have a unique way of performing their mating signals: they synchronize their flashes. Truly synchronous fireflies are found in Southeast Asia. They congregate in colony trees and blink in unison. Other species synchronize their flashes over a few-second period, appearing as waves of light and dark that ripple through the forest. These can be found on the East Coast of the U.S. from Georgia to northern Pennsylvania. Every year, thousands make pilgrimages to witness the “light show” of synchronizing Photinus carolinus at Elkmont in Great Smoky Mountains National Park and the Pennsylvania Firefly Festival in Allegheny National Forest.
Firefly populations are threatened by light pollution. Outdoor lights prevent fireflies from seeing each other’s flashes. Thus, they have a hard time finding mates. Other potential threats include habitat loss, pesticide use and climate change. Turn off your lights at night during firefly season to ensure you have a beautiful display for years to come.