Close your eyes and think back to a warm summer night, the smell of a camp fire, roasting marshmallows or eating s’mores; when all of a sudden, a young voice yells out, “There one is” and all the kids run to the blinking lights slowly rising into the moonlit sky. We all can remember the endless summer nights as kids, chasing lighting bugs or fireflies after a long day of picnics, swimming, and family gatherings. Even as parents and grandparents, watching kids run to catch their first lighting bug is magical. My granddaughter named the first one she caught Gloria, kept it in a container with grass only to have it mysteriously escape sometime during the night. So what are these blinking summer beacons of joy?
A rose is a rose is a rose, but a firefly is not a fly but a beetle. Scientifically, fireflies are classified under Lampyridae, a family of insects within the beetle order Coleoptera, or winged beetles. There are several thousand species of fireflies that inhabit the temperate and tropical regions of the world. Fireflies inhabit every continent of the world except Antarctica. In North America there are several hundred species, but none west of the middle of Kansas. Not all fireflies emit light or what is called bioluminescence. In North America most fireflies are divided into five families; however the family Photurinae and sub-family Photinus tend to be the most common. They are about half an inch long, producing yellow-green light, closely followed by the sub family Photuris which is larger, almost an inch long, producing a darker green light. It’s very difficult to distinguish Photinus from their light alone, even for other fireflies; female Photuris often mimic mating flashes from female Photinus fireflies to attract and eat Photinus males. The last sub-family is Pyractomena which produce a yellow-amber flicker that looks a bit like a spark from a campfire.
We all know that a light bulb or any type of light gives off heat and is hot to the touch. So conventional wisdom would expect the light or bioluminescence the firefly produces to give off heat. Once again fireflies are very different. The light they produce comes from a complex chemical reaction. Scientists call this “cold light”. The reaction is so efficient that 100% of the energy is emitted as light; compare that to a light bulb where only 10% is emitted as light and 90% as heat. There are several theories about how the firefly turns on and off its “light”, but one thing is for certain, there is a reason for this behavior. As we have seen time and again in nature with colorful feathers, courtship dances, males fighting for dominance, this phenomenon of bioluminescence serves primarily one purpose for the adult firefly….attracting a mate. Both male and female fireflies use their flashing lights to communicate. Some species synchronize their flashes, sometimes across thousands of insects. All species speak a “language of light”. Researchers also believe that this language of light is used to defend their territory and warn off predators. But wait, this language of light doesn’t stop with the adults; firefly larva also are bioluminescent. All known firefly larvae have photic organs and produce light.
As in colorful caterpillars, secretions in poison dart frogs and toads, and other defensive adaptations, the most generally accepted hypothesis is that firefly larvae use their luminescence as a warning signal (aposematism) that communicates to potential predators that they taste bad because they have defensive chemicals in their bodies. Adults also have a defensive mechanism. Let’s return to our kids….once the shrieks of joy subsides about catching a firefly, the shouts of “Yuck, the firefly pooped on me” soon follows. As a defensive mechanism, fireflies shed drops of blood in a process known as “reflex bleeding.” The blood contains chemicals that taste bitter and can be poisonous to some animals and can cause skin irritation in some cases. . Because of this, many animals learn to avoid eating fireflies but it doesn’t stop most kids!
Fireflies have short life spans. An adult firefly lives only long enough to mate and lay eggs. The jury is out on what they eat or if they need to eat during their adult life stage. The larvae usually live for approximately one year, from mating season to mating season, before becoming adults and giving birth to the next generation. Firefly larvae are primarily carnivorous, usually eating snails and worms. Most firefly larvae are found in rotting wood or other forest litter or on the edges of streams and ponds. Most firefly species have one thing in common: standing water. They live near ponds, streams, marshes, rivers and lakes, but they don’t need a lot of water to get by. Vernal pools …remember them…and small depressions that hold water during firefly mating season can all provide the habitat fireflies need. As any child can tell you fireflies only come out at night. During the day they spend most of their time on the ground trying to keep cool and avoid the hot sun. At night, they crawl to the tops of blades of grass or weeds and fly into tree branches to signal for mates as well as making childhood memories we keep for a lifetime.
Did you know?
Some Asian species of fireflies are fully aquatic (due to the presence of tracheal gills) and live underwater, feeding on aquatic snails.
The Boston Museum of Science is doing a research project on fireflies and encourages people to go to https://www.mos.org/fireflywatch/how_to_participate and help researchers collect data.
Researchers are using the chemical reactions found in fireflies to detect changes in cancer cells and in muscular dystrophy research.