by Marjorie Rachlin
Your backyard or local park is the stage for a magical light show each summer night. It’s firefly time. And I’ve been sitting on my back porch after sunset, watching the lights go on and off.
As it gets darker, the yellow flashes appear up in the trees, over the garden, and just above the grass.
Video from Wikipedia’s fireflies page. Here’s the original on YouTube.
I remember the excitement I felt as a kid when the fireflies came out. I would get a big glass jar, with holes punched in the lid, and run around the yard collecting until I had enough for a personal light show. After an hour or so, I let them free.
Why are they flashing?
Fireflies are not flies – they are beetles. Like all insects, reproduction is the whole purpose of life. They have a short time to mate.
Adult beetle in the family Lampyridae, commonly called firefly or lightning bug. (photo by Bruce Marlin, shared under Creative Commons license)
Males are flashing to attract a female. They are in the air and she is on the ground. She flashes back to announce her presence.
The flash makes all the difference
As a child, I didn’t know that the flashes may come in different patterns and different colors, according to the species in the yard. (Flashes are yellow in our most common species.) Sometimes there are several different species out there, but the firefly must mate with one of its own species in order to produce fertile eggs.
So how do they tell the difference? Wikipedia.com gave me that answer.
Watch carefully. You will notice that some flashes are slow and last longer than others. Some are very quick, some fast, some blink, blink, blink. Each species had its own pattern, to make sure that the right couple get together. (So far, I seem to have only one species, although there are five different ones fairly common in the mid-Atlantic area.)
Where does the light come from?
Fireflies bioluminescence comes from a chemical reaction in their body. They have organs on their abdomen that combine chemicals, oxygen and an enzyme, luciferase (which they manufacture), to produce the light. It is an amazing process which scientists have studied for years. See more below.
These photos show the same firefly, one using the camera’s flash, the other showing the firefly’s natural bioluminescence. (photos by Wikipedia user Emmanuelm, shared under Creative Commons license)
After mating, what next?
After mating, the female firefly lays eggs in the ground or just in top of it. The larvae live underground in the fall and winter, eating slugs and worms. The little firefly grubs glow, because they already have the light-making ability.
Firefly larva (photo by Wikipedia user NEUROtiker, shared under Creative Commons license)
They may stay underground a year or more – we do not know for sure. In spring they pupate and emerge as adults. Most adult firefly species live on nectar and pollen, until it’s time for the big show.
Facts about fireflies
There are 2,000 species of fireflies all over the world. The U.S. has 200 species, almost all of them east of the Missisippi River. There are probably five species common in our area.
Wikipedia.com tells me that scientists have reproduced the chemical luciferase (see above) for use in forensics and also medical uses. Gene coding for the chemical used by fireflies to produce light has been put into several organisms. Chemistry is my weak spot – Wikipedia’s luciferase page explains it well.
Citizen scientists can report firefly sightings to Firefly Watch, a project of the Museum of Science in Boston (mos.org). Volunteers email exact data, location, time of day and which firefly species they have seen. Most of these volunteers are in the eastern U.S., but a few are in Europe. Here’s a map of sightings.
Wait for sunset and see the show
You don’t need to record your observations to enjoy the magic in your backyard or in open areas in the parks. Look around 9 p.m., after sunset, and see a natural marvel.