Fireflies and lightning bugs are neither flies nor bugs, but beetles. Because of the luminous organ at the tip of the abdomen, fireflies are some of the most familiar, and surprisingly well-liked (or should I say less-feared?) insects.  It is a sad childhood, indeed, that does not contain a summer evening or two spent chasing and capturing these charming little fellows. But wait! This species pictured below is a fearful predator of other firefly species, even going so far as to mimic their flashing pattern to lure unsuspecting males to their deaths!

The firefly is capable of producing a "cold light" containing no ultra violet rays, with a wavelength from 0.00051 to 0.00067 millimeters in length, pale yellowish or reddish green in color, with a light efficiency of 96%. The ordinary incandescent light has an efficiency of roughly 10%, most of the energy being wasted as heat.

The light-producing organ is located in the sixth, or the sixth and seventh abdominal segments. Here are stored two compounds known as "luciferin" and "luciferase". A system of fine air tubes, controlled by the nervous system, bring moist air to the luciferin, oxidizing it and activating the lucifrase to produce light reflected through the thin exoskeleton of the abdomen. The firefly turns on its light when flying upward, at intervals of about 5.8 seconds. In the dark periods it coasts downward again. Hundreds of them may synchronize their flashes to appear simultaneously. The females respond about two seconds later, and the males fly toward them.

Bioluminescence is defined as "the process wherein light is produced by a chemical reaction which originates in the organism". Bioluminescence is mostly a phenomenon found at the bottom of the ocean floor, but fireflies also possess this ability. Contrary to what one might think, the glow that the fireflies give off is not used to attract or deter their prey. On the other hand, fireflies use different intermittent signals in order to capture the attention of a possible future mate. Both sexes of fireflies use a specific flash pattern that can range anywhere from a short burst to a long continuous flashing sequence. Within any given population, there are many different species of fireflies and each species has a distinct signal. Males and females locate each other by recognizing their specific sequences. Since mating is essential to survival, attracting a mate can sometime become an aggressive game. It is not unusual in this game for a specific female species of firefly to fake their signals in order to confuse and lure a male from another species for the sole purpose of eliminating him, and males of the species Photuris lucicrescens mimic other species' flashing patterns to lure them as prey .

The light that a firefly creates is the result of a combination of four different ingredients. This light is produced through a chemical reaction involving luciferin, which is a substrate, luciferase, an enzyme, ATP (adenosine tri-phosphate), and oxygen. The light producing section of the body is located in the sixth or seventh abdominal section of the firefly. It is within this cavity that the two compounds luciferin and luciferase are stored. A firefly will draw oxygen in through its complex system of air tubes and expose the oxygen to the luciferin and the luciferin will then oxidize and activate the luciferase. This will generate a light that will shine through the skeleton of the abdomen. It is important to note that scientists disagree about the method that the fireflies use to control the duration of their flashes. One theory, known as the "Oxygen Control Theory", explains that fireflies can control the length and duration of their light by regulating the amount of oxygen that they intake. If little or no oxygen reaches the part of the firefly known as the phonic organ, the chemical reaction will not be extremely strong and the light of the firefly will not shine very brightly or for a lengthy duration. Another theory, known as the "Neural Activation Theory" states that fireflies have neural control over the activity of structures called "tracheal end cells". These structures aid in the initiation of the chemical reaction. Whether or not the fireflies have physical or neural control over their ability to produce light, their method of creating the light that emanates from their bodies is extremely efficient. Very little heat is given off of this light which means that not very much energy is wasted at all.