Lightning Bugs – Nature’s Flash Dancers
Performing one of nature’s most enchanting spectacles, fireflies (or lightning bugs) are the stars of the insect world.
Despite what their common names suggest, fireflies are neither flies nor bugs, but beetles from the family Lampyridae. There are over 2,000 described species of these nocturnal wonders.
Unlike ground-dwelling, luminescent glowworms, adult fireflies are winged. They flit around all continents bar Antarctica, preferring warm and wet wooded habitats. In Australia, fireflies inhabit the forests and mangroves along the coast of New South Wales, Queensland and the Northern Territory.
Bioluminescence – How these glitterbugs get their gleam
What gives these insects their trademark glow? Fireflies are masters of bioluminescence. Bioluminescence is the production of light in a living organism by the chemical reaction chemiluminescence.
Fireflies have light-producing organs called lanterns under their abdomen. Lanterns contain photocytes, specialised cells that convert chemical energy into light. Oxygen reacts with the pigment luciferin within the photocytes. The chemical reaction, catalyzed by the enzyme luciferase (a protein that speeds up the rate of the reaction), produces a flash of light.
Fireflies produce patterns of light flashes, rather than a steady shine. Intermittent release of nitric oxide allows oxygen to cyclically build up in the photocytes, fueling bursts of reactions. The light stops once the oxygen is used up, only flashing again after more oxygen has accumulated.
Fireflies are remarkably efficient, producing a ‘cold light’. All the energy in the reaction is used to create light, rather than wasted as heat. These luminaries also vary in their glow, from yellow-green to orange, depending on the arrangement of luciferin molecules. In North America, fireflies active during the dark emit green bioluminescence, while species active during dusk emit a yellow light to ensure they’re seen amongst the greenery.
Bioluminescence is not to be confused with fluorescence, which doesn’t involve chemical reactions. An object that fluoresces absorbs and re-emits an external stimulating light (like a torch or moonlight). Without the stimulating light, there is no glow.
“The fireflies, twinkling among leaves, make the stars wonder.”
Rabindranath Tagore (1861-1941)
For these love-bugs, it really does start with a spark. Males fly around forests and open meadows in the night, flashing to attract a mate. A female charmed by a males display will glow in his direction, guiding his way to her on the ground
Timing is everything for the firefly. The rate and speed of a male’s flash dance governs his appeal, and is distinctive to each species. For some species, faster or longer flash patterns are most appealing to a female, while for others, slow or short flashes get the girl.
Some species of firefly synchronize their flashy displays, called simultaneous bioluminescence. Males congregate in groups known as leks to parade their skills, flashing their lanterns at the same time to attract females.
It’s not only the adult lightning bugs, glowing for courtship. All stages of the lifecycle, from egg to beetle, are luminescent. The light acts as a chemical and visual defence, warning predators that they are toxic to taste.
Femme fatales: mimicry and murder
Some feisty females exploit this unique mating ritual. Females of the genus Photuris use ‘aggressive mimicry’ to secure a feed. When males of another genus flash, the female responds with the flash pattern. She lures the male in, and once close enough, she eats him.
This deviant behaviour comes down to defence. Unlike other species, adult females of the genus Photuris don’t produce chemical defences. This leaves them as easy pickings for predators. By eating the males, his chemical defences are transferred to the female, providing her with protection until she mates. But the males have clued in, learning to spot the phonies to avoid being duped.
Lights out for the firefly?
The glow of the fireflies is dimming. Around the world, urban sprawl, development and light pollution are driving their decline. As forests are cleared, and open meadows are paved, fireflies are losing their habitat. Fireflies also need the dark. Light from cars, street lamps and houses interrupts their flashing patterns, disrupting their luminescent messages. If they can’t communicate, these glitterbugs will disappear.
Fireflies are remarkable creatures. With their whimsical twinkling displays, fireflies truly are the stars of the night.
See Tsuneaki Hiramatsu’s beautiful photographs of fireflies
More information on the wonders of bioluminescence
Check out these other amazing bioluminescent creatures