Marc Branham, an assistant professor in the department of entomology and nematology at the University of Florida, explains.
Fireflies produce a chemical reaction inside their bodies that allows them to light up. This type of light production is called bioluminescence. The method by which fireflies produce light is perhaps the best known example of bioluminescence. When oxygen combines with calcium, adenosine triphosphate (ATP) and the chemical luciferin in the presence of luciferase, a bioluminescent enzyme, light is produced. Unlike a light bulb, which produces a lot of heat in addition to light, a firefly's light is ¿cold light,¿ without a lot of energy being lost as heat. This is necessary because if a firefly's light-producing organ got as hot as a light bulb, the firefly would not survive the experience.
A firefly controls the beginning and end of the chemical reaction, and thus the start and stop of its light emission, by adding oxygen to the other chemicals needed to produce light. This happens in the insect's light organ. When oxygen is available, the light organ lights up, and when it is not available, the light goes out. Insects do not have lungs, but instead transport oxygen from outside the body to the interior cells within through a complex series of successively smaller tubes known as tracheoles. For a long time it was a mystery as to how some firefly species manage such a high flash rate, considering the relatively slow speed of the muscles that control oxygen transport. Researchers fairly recently learned that nitric oxide gas (the same gas that is produced by taking the drug Viagra) plays a critical role in firefly flash control. In short, when the firefly light is ¿off," no nitric oxide is being produced. In this situation, oxygen that enters the light organ is bound to the surface of the cell's energy-producing organelles, called the mitrochondria, and is thereby not available for transport further within the light organ. The presence of nitric oxide, which binds to the mitochondria, allows oxygen to flow into the light organ where it combines with the other chemicals needed to produce the bioluminescent reaction. Because nitric oxide breaks down very quickly, as soon as the chemical is no longer being produced, the oxygen molecules are again trapped by the mitochondria and are not available for the production of light.
Fireflies appear to light up for a variety of reasons. The larvae produce short glows and are primarily active at night, even though many species are subterranean or semi-aquatic. Fireflies produce defensive steroids in their bodies that make them unpalatable to predators. Larvae use their glows as warning displays to communicate their distastefulness. As adults, many fireflies have flash patterns unique to their species and use them to identify other members of their species as well as to discriminate between members of the opposite sex. Several studies have shown that female fireflies choose mates depending upon specific male flash pattern characteristics. Higher male flash rates, as well as increased flash intensity, have been shown to be more attractive to females in two different firefly species.
The adult fireflies of some species are not luminous at all, however, and instead use pheromones to locate mates. The use of pheromones as sexual signals appears to be the ancestral condition in fireflies with the use of luminous sexual signals as being a more recent development. There are species that employ both pheromonal and luminous components in their mating systems. These species appear to be evolutionarily intermediate between the pheromone-only fireflies and flash-only fireflies.
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5 Comments
Add CommentI understand the mechanics as to how the firefly lights, but still don't understand why it luminesis only when rising?
Reply | Report Abuse | Link to thisMarc, Well stated. This leads me to wonder how some of the lowest organisms in the ocean produce their luminescence, when they respond to induced stress, as they do when jostled by breaking waves in the surf, so they appear to light up the waves on a dark night, irrespective of whether there is a moon or shore lights present to contribute to their luminescence. I have seen a laboratory jar of these organisms in a dark room produce enough light upon being shaken mildly, to read by, easily. This was demonstrated to me by scientists at a National Lab who wanted to use my spectrographic analyzer to determine the wavelengths of the light produced, so as to define which organisms were most prevalent, during the fluctuation of organisms caused by pollution, and by the natural progression of species caused by predation up the chain from smallest to larger. As a species population decreased, the prevalence of that species' light intensity decreased and another, usually larger species became more prominent in population and subsequent light intensity. It was being tested to determine whether there was enough difference in the wavelengths characteristic for each species to tell which species was predominent at any given sample time, and to profile the population distribution within the body of water. This was to be used to determine the effects of pollution on the 'health' of the body of seawater, and to measure its progress during a cleanup. Since this fluctuation of populations is also a natural predation result, it is necessary to get a 'background' cycling of the populations by natural events, such as eating of smaller organisms by larger ones. As I understood, this could be used to evaluate what event had caused a population shift, and specifically what organisms had been affected.
Reply | Report Abuse | Link to thisOn the evening of June 17th, following a summer lightening and rainstorm in Blue Earth, Mn, we noticed an unprecedented number of fireflies in my back yard, near the Blue Earth River, in the floodplain. We estimate there were as many as 100,000 or more! The light emissions were so spectacular as to exceed the 4th of July fireworks display. Never in all of sixty five years have I witnessed such a display. Why the numbers, and why tonight?
Reply | Report Abuse | Link to thisWe had a similar experience last night - they sky was alight with hundreds of flashing fireflies, and only in the back yeard; not in the front yard...there was a full moon and it has been very hot, unusually so for June. I hear there is an eclipse early tomorrow morning.
Reply | Report Abuse | Link to thisGreat information. Thank you!
Reply | Report Abuse | Link to thisMicah Wood
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