July is lightning bug month.
Whatever you call them—lightning bugs or fireflies—many of us have memories of going out in the early evening to catch them in a jar. Lightning bugs and fireflies are neither bugs nor flies, but a beetle from the insect family Lampridae, which in Greek aptly means “to shine.”
There are more than 2,000 different fireflies in the world and about 150 in North America. The most regularly seen species in Connecticut is the Common Eastern Firefly or Big Dipper Firefly (Photinus pyralis), so named for the dipping, J-curved flight pattern of the males.
Why do they blink? Scientists think this has to do with courtship and mating. In most species, it’s the males who fly and flash, and look for females. Females don’t fly, but hang out in trees, shrubs, and grasses, and flash in response.
But all is not wine and roses in this courtship ritual. There’s another species, Photuris versicolor, whose females imitate the flashing signals of Photinus pyralis females. These females lure in Photinus males and eat them to get the chemical that makes these males taste bad to predators like wood thrushes.
Imagine planning your vacation around the remarkable display of fireflies that flash all at the same time. That’s what visitors to the Great Smoky Mountains do every year. They enter a lottery for a chance to view Synchronous Firefly (Photinus carolinus). For the lucky ones, it’s an amazing experience.
Here in Connecticut, you can see fireflies flashing from the last week of June through most of July. Typically, adults live only three to four weeks. The time spent as both an egg and pupa (resting stage) is also not long, about three weeks. That’s a relatively short time compared to how long it will spend as a larva, which is one to two years, or 95% of its life cycle! Fireflies undergo complete metamorphosis: egg–larva–pupa–adult.
Larvae also release light and so are nicknamed glow worms. It is thought that this glowing warns potential predators that they taste bad. Although some species of adult fireflies are predatory, many feed on plant nectar and pollen. It’s the larvae who are carnivores, living in the soil or leaf layer eating snails, slugs, and other invertebrates, which makes them great to have around the garden.
How do fireflies produce light? A chemical reaction inside their bodies allows them to light up. This kind of light is called bioluminescence. This light is produced when oxygen combines with calcium and a chemical called adenosine triphosphate (ATP), along with the chemical luciferin in the presence of the enzyme luciferase. Luciferase has been very important in medicine, and has been used to track tumor cells, bacterial and viral infections, gene expression, and the response to treatment.
Like many insects, firefly populations are threatened. This is possibly because of habitat loss, the use of pesticides on our lawns and gardens, the overuse of outdoor lighting, and invasive plant species. What can you do to help? Don’t rake leaves to put them on the curb. When you do that, you are raking up firefly larvae and throwing them away. Instead, leave them under shrubs and trees to provide a healthy organic mulch. If you have poor soil, introduce nutrients by adding compost, leaves, and other organic matter. Avoid broad-spectrum pesticides, especially lawn chemicals. Turn off outside lights and advocate for local “Dark Sky” policies to control light pollution, or at the least install security lights on a timer. Plant native shrubs, trees, grasses, and perennials. A cottage garden with thick cover will imitate the field edge that fireflies like. Many fireflies prefer moist areas, so consider putting in a small water feature surrounded by native vegetation. With these proper conservation steps, we can assure that these amazing creatures won’t blink out.