Firefly Fancy

Firefly Fancy
shared by Melissa Donahue, Naturalist 
melissa.donahue@nashville.gov
Late May 2020

The light is fading behind the hackberry tree in the backyard.  I am sitting on my back porch with a soft head on my shoulder.  Whispering quietly, we are settling down for one of my favorite early summer activities with some of my favorite people.  The day has been warm, but the night is pleasant and not muggy.  We peer into the night with great anticipation.  We, my husband and two grandchildren and I, are looking for the first firefly of the evening. 

There are 25 species of fireflies in Tennessee with Photinus pyralsis being the most familiar.  At least 19 of these species are found in the Great Smoky Mountains.  Our plan was to be camping in the Great Smoky Mountains this year.  The main attraction this time of year is the synchronized fireflies near the Elkmont campground.  This species, Photinus carolinus, is the only species in America whose individuals can synchronize their flashing light patterns. 

Check out this video of the Smoky's synchronized fireflies

Fireflies (or lightning bugs) are not flies or true bugs, but a beetle in the family Lampyridae.  They take from one to two years to mature from larvae. A few days after mating the female lays her eggs on or just under the soil.  In 4 weeks, the larvae will emerge. In this larval stage, this insect lives underground for one to two winters and feeds on snails and smaller insects. They are avid hunters, injecting their prey with a paralytic substance before consuming it.  Most fireflies pupate underground or in rotting logs, although some attach to tree trunks and emerge in early spring or summer when the temperature and rainfall are just right. 

An adult firefly is about 2 cm long.  Different species eat different things: some eat nectar, other insects or nothing at all. Some species of fireflies feed on other fireflies—most notable is the genus Photuris, which mimics female flashes of Photinus, a closely related species, to attract and devour the males of that species.

Each species of firefly has a characteristic flash pattern. Called bioluminescence, it occurs when oxygen and the organic compound luciferin react together in the presence of the enzyme luciferase. This creates a “cold light” that uses 100% of the energy to produce light, and therefore no heat is produced.  This light is usually greenish-yellow but can be other colors, including one species that produces a bluish light. This allows the insects to flash.  The flashes help the male and female communicate, mark territory and warn away predators.  The males flash about every 5 seconds and the females flash about every two.  In most species, the female waits in the grass or on trees and shrubs while the male flies and flashes. When an attractive male appears, she will signal with a flash of her own.

photo credit Cosmos magazine

Just as the final light fades, we see our first flash.  Awed, we sit in a hushed quiet while flashes of lights rise up from the grass and bushes.  Then we grab our jars with holes in the lids and, laughing, head into the yard to catch our night lights.  We carefully observe the beetles, and then let them fly away and head to bed.