Fireflies, also known as lightning bugs, are not actually members of the fly family. They are actually beetles, and only have the ability to fly during their very short adult phase. As a general rule, genuine members of the fly family have two-part names, while other flying insects have one-word names. House flies and tse-tse flies are indeed flies, while fireflies and dragonflies are not. It's a distinction only an entomologist could love.
These bugs begin their life cycles as fertilized eggs implanted into damp soil. After three weeks, immature larvae emerge and essentially become eating machines. Young fireflies capture small prey, such as snails, worms, and mites, and inject them with a powerful acidic juice, much like spiders. The immature larvae will then suck out the dissolved body tissue. They remain in this immature larval stage for one or two years, building up "mud houses" to protect themselves as they grow into pupa and eventually into the adult lightning bugs we see during summer months.
Adult fireflies emerge from the pupa stage fully formed. For the next three weeks or so, their only missions are to eat, sleep, and make more fireflies. To accomplish their mating mission, they are equipped with special chemicals which create a cold light, known as bioluminescence.
One chemical is called luciferin, which one could think of as the log for a fire. Another chemical, luciferase, is an enzyme which acts as the catalyst for luminescence. You can think of this as the lighter fluid poured on the log. Finally, a chemical called adenosine triphosphate (ATP) ignites the luciferin-luciferase combination in a controlled glow inside the bugs' yellow-green abdomens.
There is a purpose for all of those fireflies blinking during the early evening hours. Females, which are generally wingless, remain on the ground and watch for certain flashing patterns from their male counterparts. This helps them identify members of their own kind.
Once a match has been found, the males land near the females and consummate the mating ritual. The females deposit their fertilized eggs into the ground and the entire life cycle begins anew. Adults rarely live past the late summer months.
Because adult fireflies do not bite or carry diseases, they have always been a source of fascination for people. Many children spend a few hours on warm nights capturing and releasing fireflies. There is a significant amount of scientific interest in them as well. The chemicals used to create their glow are very rare outside of the insect world.
Researchers have been using supplies of luciferin and luciferase to study their effects on diseases like cancer and muscular dystrophy. Because ATP is present in all life forms, scientists can also detect the presence of harmful bacteria by using test strips infused with luciferin and luciferase. If the test strip glows, a living organism is most likely present.
There have long been rumors that some companies routinely pay volunteers to capture fireflies for research purposes. The good news is that sometimes, the rumors are true — there have been companies that indeed purchase fireflies for a number of projects. The bad news is that the pay rate is not especially high, averaging around 1 US cent per specimen. Captured fireflies must be stored and shipped under precise conditions as well. The professional harvesting may have to remain an elusive dream for young entrepreneurs.