Nature’s fireworks: Fireflies’ bioluminescence

The first firefly of the year appeared in my yard a month ago. As fireworks commemorate Independence Day, I’m reminded of the natural fireworks that go on all summer long.

Fireflies or lightning bugs

First, though, a few words of clarification. Fireflies, or lightning bugs as my dad called them, are neither flies, nor bugs. They are beetles. About 2,000 species belong to the family Lampyridae, insects capable of bioluminescence.

The light that fireflies produce is nothing short of amazing. It is cold light, produced biochemically with little energy lost as heat. Compare that to an incandescent light bulb that gets too hot to touch in just minutes. New compact fluorescent bulbs are more efficient and produce much less heat, but science still longs to produce a source of cold light.

The process

The bioluminescent organs of fireflies are located on their abdomen. In the cells of the light organs, which are richly supplied with air tubes, is a chemical called luciferin.

When luciferin combines with oxygen in the presence of the enzyme luciferase, the chemical reaction releases energy in the form of light. Reflector cells in the light organs magnify the intensity of the light so that’s it’s impossible to miss nature’s light show on a warm summer evening.

Control

Fireflies control their flash patterns by regulating the amount of oxygen that reaches the light organs through the air tubes. Consequently each species flashes a specific pattern that’s used to communicate during the breeding season.

Firefly flash patterns vary in a number of ways from species to species. Color ranges from almost white to yellow and green. The duration of each flash, the interval between flashes, and the number of flashes varies. Finally, different species are active at different times of night, and each has a distinct flight pattern.

This is a very effective means of communicating and would work perfectly if no one cheated. But some fireflies cheat.

Friend or foe?

For example, females of the genus Photuris can mimic the flash patterns of female Photinus fireflies. A male Photinus firefly, flying about the edge of the yard, may see this flash coming from a tuft of grass or a shrub and approach with the idea that he has found a receptive mate. However, when he gets close, the Photuris female, who is double his size, can seize and eat him.

The male Photuris can play a similar game. He can imitate a male Photinus in hopes of attracting a hungry female Photuris. While she flashes to lure in the male “Photinus,” the male Photuris can get close enough to reveal his true identity and mate.

This game of who’s who can be difficult to follow. It’s a level of deception and trickery worthy of a Shakespeare play.

Patterns

It’s easy to study the flash patterns of the fireflies in your backyard. I call it “gee-whiz science.” After identifying the length and rate of the female flash pattern (the one in the grass), mimic it with a flashlight. If your impression is good, males will approach in search of a receptive female. If you can identify several different flash patterns, you will have identified several different species of fireflies. It’s much like recognizing different birds or frogs by their voices.

Fewer fireflies

Unfortunately, people see far fewer fireflies today than they did when they were growing up, and entomologists don’t know why. Some speculate that firefly numbers are down because of our lawn care habits. During the day fireflies rest in the grass and they may succumb to the blades of lawn mowers. Or perhaps our overuse of lawn chemicals is taking a toll.

Light pollution

Another possible problem, especially in urban and suburban areas, may be light pollution. Street lights and backyard security lights may disrupt fireflies’ ability to detect and interpret flash pattern of the opposite sex.

Whatever the problem, scientists at the Boston Museum of Science oversee a citizen science project to assess firefly populations. Though the original intent was to limit the project to Massachusetts, word of the project spread quickly, and after just two years more than 2,000 volunteers participate.

To devote as little as 10 minutes each week to monitor firefly numbers in your backyard, visit www.mos.org/fireflywatch for details.

You can also visit a blog by Shalaway.