What's in Flight
As twilight descends each evening, the park starts to glitter with little pulses and flashes of light. It’s firefly season. And as Dr. Sara Lewis, a firefly specialist and biologist at Tufts University remarked: ‘Fireflies can transform our landscape into something ethereal and magical.’
Fireflies and Black-eyed Susan
One of the most famous eastern fireflies (Photinus pyralis) is also the most common in our park. It is also known as ‘the Big Dipper’ because the courting males do a J-shaped dance while flashing their lanterns. Female fireflies sit on low vegetation and watch. If one is interested, she flashes back a come hither signal. This silent love song is repeated several times. Once a pair of fireflies have established compatibility, they hook up tail-to-tail for hours. During this time, the male passes along his sperm and ‘a nuptial gift’ in the form of proteins that will help nourish the eggs.
Firefly, clover and full moon
There are over 2,000 species of firefly in the world and to date 36 species have been documented in New York State according to Candace Fallon, a senior conservation biologist at the Xerces Society. ‘The flashing species of firefly uses different colors and patterns to signal their presence. The ones we see at dusk often flash more yellow.Those after dusk flash more green. Some lanterns appear amber, or blue like the ‘Blue Ghost’ firefly in North Carolina. Some fireflies flash at lower heights like the Big Dipper and others prefer the tops of trees. And some species don’t flash at all. Fireflies that are active during the day communicate via chemical signals called pheromones.’
Yellow flashing fireflies
Signaling female firefly
Not all firefly courtships end well. There is a vampire firefly in our park (of the Photuris genus). She mimics the flashes of the Photinus females, so she can prey on their males, sucking their blood and devouring them. Dr Sara Lewis explains: ‘Most fireflies manufacture protective chemicals that are toxic to birds and other insects. But we think these femme fatales have lost the ability to make toxins, so they drink other fireflies blood to ingest these chemicals.’
Blue Ghost fireflies float lowdown and have a dim longlasting glow
Peak period for spotting fireflies is between the end of June and the end of July. They are only in flight for a couple of weeks. It is the culmination of a long uneventful life. They spend up to two years in a larval stage, grubbing about in moist soil, leaf litter and rotting wood. As such, they are a precious part of the park’s ecosystem, helping decompose organic matter and voraciously eating earthworms, slugs and snails.
Photuris firefly with green lantern
When tracking fireflies, do note that you won’t see many flashing their lanterns on the park’s boardwalk along the river. ‘Fireflies don’t like bright lights. Light pollution is one of several reasons for their decline,’ says Candace Fallon. The fireflies are flashing out a signal in hopes of finding a mate. And if they can’t see each other’s lanterns, then they cannot reproduce. Like courting lovers, fireflies prefer the darker recesses in the park – especially the lawns, walkways and bushes between 86th and 89th street around Gracie Mansion.
Green flashing fireflies
Firefly on a wood anemone
These little bioluminescent flying beetles are not only enchanting, they also contain a spark which is kindling scientific breakthroughs. As Candace Fallon explains, the enzyme luciferase, which makes firefly lanterns glow, is already being used to help detection of HIV transmission and blood clots in humans. And in the future it may also help detect cancers. And there is something else. Firefly lanterns may hold the key to more efficient forms of illumination. 100 percent of the energy in their lantern is converted into light, which makes them the most energy efficient light source on the planet.
Firefly on a thistle
Words: Lucie Young
Why firefly populations are declining
How we can help the fireflies
Dr Sara Lewis’s TED talk on fireflies