Fireflies Illustrated

One of the few positives about hot and humid summer days here in the east is the appearance of fireflies (1). I think I became aware of these little beetles when I first rode the Pirates of the Caribbean ride at Disneyland. Those little faux creatures were probably light emitting diodes hanging from black-colored wires that gave the appearance of small Christmas lights strung out across the bayou - blinking on and off to the plucked stings of a banjo. My next encounter was as a graduate student trying to repeat seed energetics experiments using a liquid scintillation counter. A carefully measured amount of luciferin-luciferase (2) reagent was injected from a micro-syringe into a cocktail of ground up sugarbeet seeds and chemical buffers in the hope that the resulting amount of light that glowed was proportional to the amount of active adenosine triphosphate (ATP) in the seeds - an indicator of the energy capacity of the sample. The relevance of all this is that the source of the glowing concoction was none other than fireflies that were raised for their abdomens in a controlled environment by a chemical supply company - they gave their all for science. A professor of mine in graduate school, Te May Ching, refined this technology for studying the vigor of seeds.

For those poor little ones - there was no justice.

Jump ahead 25 years, it was early June 2006 and my wife was making final preparations for her move East to join me. On my way West to join up, attend our youngest's high school graduation, watch the movers pack up our house and turn our keys over to the new owners, see our second grandson born, then fly back to Maryland, and three days later deliver our son to the Naval Academy - I went south to Georgia to do location visits at two of my agency's laboratories, and speak at a conservation society meeting in the mountains north of Atlanta. After arriving at Watkinsville, one of my friends at the laboratory invited me to join him and his wife for dinner at their home - Southern hospitality. After sitting out on their back deck - perched over a steep grade that dropped down through the woods to a creek - and having an enjoyable dinner and conversation, my host offered to show me the front yard. We went through the house and out the front door where to my amazement was a stunning display of twinkling lights covering the shrubs and trees. When I asked Harry how he had set out all of those twinkle lights, he just laughed and said: "Those aren't twinkle lights, those are lightning bugs!" - it may as well have been a Southerner taking a city-raised Yankee out for a snipe hunt (3). Even this past week, three years later, he mentioned that he had told someone that story about me.

The bug's revenge - there is justice in the world.

Regardless of how hot and humid the day, I know that the pleasure of fireflies' company will be the summer's treat - I can count on it. Whether taking a walk down the street in the neighborhood, or sitting in the backyard with the patio light off.... the silent, cool flashes of these floating wonders against a dark background will be there - an evening display well worth the wait (4).

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(1) Lampyridae is a family of insects in the beetle order Coleoptera. They are winged beetles, and commonly called fireflies or lightning bugs for their conspicuous crepuscular use of bioluminescence to attract mates or prey. Fireflies are capable of producing a "cold light", containing no ultraviolet or infrared rays. This chemically-produced light, emitted from the lower abdomen, may be yellow, green, or pale red in color, and has a wavelength from 510 to 670 nanometers.

There are more than 2,000 species of firefly found in temperate and tropical environments around the world. Many species can be found in marshes or in wet, wooded areas where their larvae have abundant sources of food. These larvae can also emit light and are often called "glowworms", particularly in Eurasia. In the Americas, "glow worm" also refers to the related Phengodidae.

(2) In luminescent reactions, light is produced by the oxidation of a luciferin (a pigment):

luciferin + O2 → oxyluciferin + light

The most common luminescent reactions release CO2 as a product. The rates of this reaction between luciferin and oxygen are extremely slow until they are catalyzed by luciferase, sometimes mediated by the presence of cofactors such as calcium ions or ATP. The reaction catalyzed by firefly luciferase takes place in two steps:

luciferin + ATP → luciferyl adenylate + PPi

luciferyl adenylate + O2 → oxyluciferin + AMP + light

The reaction is very energetically efficient: nearly all of the energy input into the reaction is transformed into light. As a comparison, the incandescent light bulb loses about 90% of its energy to heat.

(3) A snipe hunt, a type of practical joke that involves experienced people making fun of newcomers by giving them an impossible or imaginary task. The origin of the term is a practical joke where inexperienced campers are told about a bird or animal called the snipe as well as a usually ridiculous method of catching it, such as running around the woods carrying a bag or making strange noises. Incidentally, the snipe (a family of shorebirds) is difficult to catch for experienced hunters, so much so that the word "sniper" is derived from it to refer to anyone skilled enough to shoot one.

(4) The numbers of fireflies where we live are not at all as great, so the displays here are not as spectacular as the one I saw in Georgia. But here the advantage is I can watch and concentrate on only one or a few at a time - following each one's path, either slowly flying on a calm night or invisibly catapulted by a breeze between flashes to the next sighting. The pleasure of studying one here is inversely proportional to the attention to each in a great crowd, but together they provide the same collective pleasure as watching one alone.