Photo: Common Eastern Firefly, Judy Gallagher
Cliff Fairweather, Judy Gallagher, and Betsy Martin
Is there a more magical sight than fireflies flashing on a June evening? Who can forget the childhood delight of catching fireflies, cupped gently in hands to peek at the flash close up? It’s no wonder the collective noun for fireflies is a “sparkle.” Read on to learn more about our local fireflies and how to attract them to your yard.
If fireflies are flashing, you can be sure mating is going on, because flashing is all about signaling potential mates. Males often make elaborate flash displays in flight, while receptive females make simpler response flashes from the ground or a low perch.
Photuris species, the femme fatales of fireflies, Judy Gallagher
Some fireflies are deceivers, though, and their flashing is not about mating at all. Adult females of the genus Photuris eat the males of other species, which they lure and capture by imitating the flash pattern of receptive females of that species. These femme fatales obtain a defensive chemical from their victims, a steroid called lucibufagins, that makes the Photuris females and their offspring distasteful.
Fireflies or, if you prefer, lightning bugs, are neither flies nor bugs -- they are beetles in the family Lampyridae. Most are bioluminescent, meaning they produce light in special organs (called lanterns) that use chemical energy to produce light in a process that is nearly 100% efficient, as compared to the 10% or less efficiency of an incandescent light bulb. Not all species produce light in their adult stage, and these darkflies are active in daytime.
According to the Loudoun Wildlife Conservancy, about 20 firefly species are found in Northern Virginia. Adults of three common genera in our region (Photinus, Photuris, and Pyractomena) are distinguishable by the color and timing of their lights: yellowish flashes earlier in the evening for Photinus, greenish for Photuris, and deep yellow to orange later in the evening for Pyractomena.
Pyractomena species firefly larva, Judy Gallagher
All firefly larvae are bioluminescent, but they cannot control their light to create distinct flash patterns like adults. You might see their intermittent glow on the ground in spring or fall. Some firefly pupae and eggs also glow.
Fireflies spend most of their lives in the larval stage, during which they hunt and consume soft-bodied invertebrates, such as earthworms, snails, and slugs. They pupate underground, in rotting logs, or sometimes in the furrows of tree bark, where they spend the winter, emerging the following spring or summer.
Fireflies are more numerous in undisturbed habitats, but by paying attention to their habitat needs, you may bring them to your yard, even in an urban setting.
Most fireflies prefer moist habitats, such as wet meadows and other wetlands, stream sides, and pond edges. Let native vegetation grow up along ponds and creeks to provide cover. Leave areas of leaf litter, rotting logs, and undisturbed soil on your property to provide shelter for all life stages of fireflies: eggs, larvae, pupae, and adults – and for their invertebrate prey. By planting a diversity of native plant species and layers (from low growing herbaceous plants to trees), you will provide sites for courtship, mating, egg laying, hunting, and pupation, and preserve soil moisture, which is essential for fireflies.
Avoid using pesticides, and avoid fertilizers, especially those containing ammonia, which kill the slugs, snails, and worms that firefly larvae eat. Avoid using tree bands to trap pest insects on trees with deeply furrowed bark favored by fireflies (such as oaks and hickories), as these can also trap fireflies.
Fireflies need darkness so their flashes can be seen by potential mates. Outdoor lighting can significantly interfere with firefly courtship. Turn off the lights when possible, and consider following the International Dark Skies Association Principles for Responsible Outdoor Lighting.
And your kids and grandkids may delight in the old pleasure of collecting fireflies in a jar—just be sure to let them go right away so they can get on with making new fireflies!
Fireflies are one of several dozen Sanctuary Species at the heart of the Wildlife Sanctuary program. Learn more about the habitat needs of fireflies and other Sanctuary Species here. If you create habitat that brings 10 Sanctuary Species to your yard, your property can be certified as a Wildlife Sanctuary. Our motto is, “Let the critters decide.”