Fireflies: Nature’s Luminaries

Jennifer NicholsField Notes

When I decided to write about fireflies, I thought I would write a short, inspiring, little article about how these magical insects light up summer nights.  But like many subjects in environmental landscaping, it didn’t turn out to be that simple, so I would like to share what I have learned about these fascinating creatures.

Fireflies in Pennsylvania

I was inspired to discover that the lightning bug is the state insect of Pennsylvania. And we have a group of students from Highland Park Elementary School in Upper Darby to thank for that!  In 1974, these students discovered that there was a specific species of firefly called Photuris pennsylvanica.  No other state had named a firefly as its state insect, so the students started a campaign which included letter writing, petitions, and bumper stickers.  Eventually, their bill was signed into law, and now Photuris pennsylvanica is the Pennsylvania State Insect.  Way to go Highland Park Elementary!

Photurus pennsylvanica

Firefly Life Cycle

I also found out some other interesting information about fireflies.  Fireflies can glow in every phase of life; egg, larva, pupa, and adult. In our area, the life cycle of a firefly is one to three years.  A few days after mating, the female firefly lays her eggs on the ground, which hatch in several weeks.  The lightning bug larvae, sometimes called glowworms, then overwinter in the soil, or hidden in leaf litter.  Firefly larvae are predatory, meaning they eat other larvae, worms, and snails.  This is important because predatory insects keep other insect populations in check.  Sometime in late spring, the larvae pupate, and then emerge into adults. Adults live for several weeks, enchanting us by lighting up our summer nights.

Lighting Up

The lighting displays of fireflies are amazing!  Lightning bugs light for communication.  They light to warn off predators and to defend territory, but mostly they light to find a mate.  In Pennsylvania, males fly around at night and light up, while females wait in trees, shrubs, and long grasses.  When they find an attractive mate, females light up in response.  Studies show that females are attracted to males that can flash the fastest.  Different species of fireflies light up in different patterns, and in different colors, such as green, yellow, and orange.

Firefly Tricks

The female Pennsylvania Firefly (Photuris pennsylvanica) uses this to her advantage, in what we call animal mimicry.  She will often mimic the pattern of a different species, specifically the Photinus, or Common Eastern Firefly.  When a male Eastern Firefly lands to mate, she captures him and turns him into a quick meal.  Not to be outdone, the male Pennsylvania Firefly often mimics the Eastern Firefly male, hoping that a hungry female Pennsylvania Firefly will try to lure him into a trap.  When he lands near a female, he then convinces her that he is a mate, not a snack.

Fireflies in Decline?

One thing that complicated my writing was that populations of fireflies, or lightning bugs, seem to be in decline.  Although there is strong anecdotal evidence for this decline, there is little scientific evidence about firefly populations.  It appears that we have been taking them for granted.  To gather more information about firefly populations, the Museum of Science in Boson, Tufts University, and Fitchburg State University have teamed up on a 10-year study called Firefly Watch.  Volunteer citizens can collect backyard data and submit it for further study.  Sign up at Firefly Watch.

Why the Decline?

The two main reasons for the decline in firefly populations are habitat destruction and light pollution.  Fireflies spend most of their lives among moist leaves on the ground, often near fields, ponds, and marshes, and will mate and lay eggs in the area they were born. Development and poor land care destroy this habitat.

Light pollution is the presence of artificial light in the night environment. It often lights up whole neighborhoods at night, disrupting the ability of fireflies to communicate.  Light pollution can also affect populations of other nocturnal animals such as moths and owls. To learn more read about responsible, Tasteful Outdoor Lighting.

What You Can Do

Even though we are not certain what is causing the decline in firefly populations, it makes sense to use good land management practices to ensure that these magical insects continue to light up our summer nights.  Here is a list of what you can do:

  • Let leaves accumulate – Since firefly larvae live in leaf litter, leaving the leaves on the ground is an important step in protecting their habitat.  Remove leaves from turf areas only, and let the rest of the leaves be.  If you want a more refined look, chop leaves, and place them in beds as a natural mulch.  The less turf you have on your property, the more habitat will be available for a variety of creatures.
  • Fallen logs are great habitat –If you must take down a tree on your property, consider leaving the trunk as a fallen log.  It can be a focal point or a place to sit, and many insects, birds, and animals will use fallen logs for food and shelter.
  • Reduce pesticides – Pesticides can not only harm fireflies, they can wipe out other insects on which fireflies feed.
  • Let grass grow – Higher grass is better than low grass for fireflies. Designate some of your property areas that get mowed only once a year, or better yet, install a wildflower meadow!
  • Turn off the lights – Light pollution disrupts the ability of fireflies to communicate, find each other, and mate.  It also makes it harder for us to see them.  So turn off the lights, and appreciate these magical creatures and delight in the darkness of a summer night.

If you would like to learn more about fireflies, there is terrific information at Firefly Conservation & Research. And if you would like help in making your property firefly friendly, you can always ask GreenWeaver!