Fireflies: The Twinkle in Nature's Eye
(Page 3 of 4)
June/July 2004
By Terry Krautwurst
When a female spies a male winking her kind of wink, she waits a precise interval specific to her species and then answers back in kind. The male then responds, also after a species-discerning interval, and a dialogue ensues. In some types, the conversation is straightforward and always results in mating. In others, the outcome is less certain. Males that flash faster or brighter than the average suitor may get an enthusiastic, superbright come-hither response from the female, while lackluster Lotharios may get a cold shoulder — a ho-hum dim blink — or no more talk at all.
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Meanwhile, throwing a potentially fatal kink in the goings-on are predatory females — members of the genus Photuris" who have learned to imitate the codes of at least seven other species. Hungry for more than love, they lure unsuspecting males in, then gobble them up. Because adult fireflies live for only a few weeks and with the sole purpose of mating, many kinds eat nothing at all, or only pollen or nectar. All firefly larvae, though, are voracious predators, particularly of slugs and snails. This is great news for gardeners; firefly larvae live in and on the soil for up to two full growing seasons before pupating and emerging as adults.
Light Fantastic
Of course, it's the firefly's light production that fascinates humankind most, and rightly so. One of our most prized contrivances, the incandescent light bulb, can't hold a candle to the lightning bug. The bulb: 10 percent efficient; 90 percent of its energy lost as heat. The bug: 95 to 99 percent efficient; 1 to 5 percent of its energy lost as heat.
And this occurs within a space about the size of ... well, the word "of." A firefly's light organ consists of two layers of cells within the insect's abdomen. The upper layer is made of reflector cells that intensify the light, like the chrome behind a car's headlight. The bottom layer contains a compound known as luciferin and a reaction-instigating enzyme called luciferase. Both layers contain an array of air tubes through which oxygen can enter. The other major player in firefly magic is ATP or adenosine triphosphate, a protein found in the cells of all living organisms. It is the basic source of energy for all cell activity. Every blink of an eye, every pulsation of a paramecium, is powered by the universal currency of cell energy, ATP.
So of course ATP is in firefly cells, too. When oxygen and luciferin combine in the presence of luciferase and ATP, a chemical reaction occurs and energy is released in the form of light. Scientists aren't sure how, but it's clear that a firefly can control its flashes. Some entomologists think that an adult firefly's real distinction may be its ability to turn the light off, since immature stages — eggs, larvae (sometimes called "glowworms" ) and pupae — glow constantly. The beauty of the chemistry here, other than the lovely light produced, is that it can be used in laboratories to test for the presence of otherwise invisible life such as bacteria. Because luciferin and luciferase produce light only in combination with ATP, which exists only in living cells, tests that utilize firefly chemicals can quickly measure bacteria levels in meat and dairy products and municipal water supplies — no glow, no problem. Likewise, physicians can use such tests to detect bacterial infections.
