Fireflies in Your Backyard

July 26, 2013


Anyone can be a naturalist. In each issue of Academy Frontiers, our scientists and staff share their knowledge to help you explore the natural world. In this issue, live invertebrate specialist Karen Verderame explains the glow of summer’s most fascinating fliers.

Have you spotted some luminous creatures in your local park or backyard this summer? You may know these insects as lightning bugs or fireflies. Actually a type of beetle, fireflies have leathery front wings with the hind wings (which do all the flying) folded underneath when the insects are at rest. Although several species may live near you, you are most likely to see the common eastern firefly, Photinus pyralis. This firefly is about one-half inch long as an adult. It is adorned with a black head and blackish-brown upper wings that are outlined with a narrow yellow margin, and it has an orangey-red thorax (between the head and the abdomen) that has a black spot in the center.

Fireflies carry the chemicals luciferase and luciferin, and they use their nervous systems to ignite a chemical reaction to “turn on” their recognizable flashes. This mysterious phenomenon, called bioluminescence, is featured in the Academy’s current special exhibit, Glow: Living Lights. Fireflies use their lights primarily to communicate with potential mates. Some species of female fireflies wait on the ground until they spot these flashes, and then they attract mates by answering with their own signals. Various firefly species have distinct signal patterns and different colored flashes.

Fireflies are commonly found in suburban and rural locations. These areas tend to be much darker than cities, which are filled with bright lights that can interfere with fireflies’ signaling systems. Since most fireflies are nocturnal, it’s easy to spot them at night. They linger near streams or standing water, in high grasses of meadows and suburban backyards, and near the edges of forests. You will only see them when it’s hot and humid during the summer.

Fairmount Park in Philadelphia is a great place to find and observe fireflies because it offers plenty of waterways, trees, and uncultivated spaces. Pick an evening to visit, and try to spot fireflies in their natural environment. Track one firefly for several minutes to figure out its pattern of flashes. Bring a flashlight with a beam covered in blue paper so you can mimic the pattern without disturbing the fireflies. 

To attract fireflies to your suburban backyard, you’ll have to do a little planning. Start by mulching your yard with fall leaves to give firefly larvae a place to develop and find snails to eat. You also can ask a family member responsible for grass cutting to leave a small uncut patch or cut all the grass about 2–3 inches high. Plan to turn off any bright outdoor or indoor lights that could distract the fireflies.

Whether you’re searching in a park or at home, bring an adult and a few materials to help you observe the fireflies and record your findings. Fill a glass jar with tall grasses or leaves for the fireflies to perch on, and add a cotton ball soaked in water. Catch several fireflies and place them into the jar. Are any of the fireflies signaling back and forth to each other? What patterns are they flashing? Record your findings in a journal. Then be sure to let the fireflies out of the jar after one hour so they can enjoy their life in the wild!

You will need:

  • Flashlight covered in blue paper
  • Bug spray
  • Medium glass jar with lid
  • Tall grasses and leaf litter
  • Small twig
  • Cotton ball soaked with water
  • Journal
  • Pencil
  • Watch or timer
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