The intermittent yellow lights flashing in my backyard have reminded me of one of my favorite beneficial insects, the lightningbug (or firefly). Did you know it was also selected as Indiana’s state insect in 2018?
Say’s Firefly, Pyractomena angulata, became Indiana’s state insect when legislation proclaiming it as such was signed by Gov. Eric Holcomb on March 23, 2018. Thomas Say, who lived from 1787-1834, was an eminent naturalist who worked in New Harmony, Indiana in Posey County, and is considered the Father of American Entomology.
Lightningbugs, also known as fireflies, have fascinated young and old alike on warm summer days. I used to take my young son and daughter into the yard for some "catch and release" fun with lightningbugs. I think the exercise helped my children become less fearful of insects, as many young children tend to be. We would put them in a glass jar to watch them alternately produce their bright, yellow light, and then let them go. That’s not the traditional meaning of catching lightning in a bottle, but it's as close as we came.
Fireflies are beneficial insects native to Indiana, with a light produced by some fascinating science. Much of what we know about the firefly’s flash chemistry was discovered by Bob Hillingsworth, Larry Murdock, and associates at Purdue in the 1980s.
Retired Purdue entomologist, Tom Turpin, said the fireflies’ light comes from a chemical reaction that takes place in special cells in their abdomen, called “photocytes.” (“Photocytes” means “light cells”). The photocytes contain two chemicals that are essential to making light, luciferone and luciferase. “The chemicals are named after Lucifer, the fallen angel of light,” Turpin said.
When the firefly pushes oxygen into the photocytes, the oxygen, luciferin, and luciferase combine with two other chemicals, magnesium and ATP. (“ATP” is short for “adenosine triphosphate.”) Turpin said that ATP is a compound that all living plants and animals use as energy in their cells; your body turns most of the food you eat into ATP.
When luciferin is combined with ATP, or the fuel, and oxygen, which adds even more fuel, the luciferin is transformed into a very-high-energy chemical. It is unstable in its high-energy form, however, and as it reverts to its normal state it gives off energy in the form of light. Turpin said scientists call this process “bioluminescence,” because it's the production of light (luminescence) by a biological process.
“The chemical reaction is controlled by the amount of oxygen the firefly lets into its abdomen,” Turpin said. “That's why if you smash a firefly, or if one gets smashed on the windshield of your car, it glows very brightly for a short time. Suddenly the luciferin is exposed to the unlimited oxygen supply in the air. It's like using a bellows on a fire.”
Fireflies use the light to find each other in their mating rituals, to warn each other of danger, and to tell birds and other insects that fireflies aren’t a good meal. (The latter doesn’t always work).
Retired Purdue entomologist Arwin Provonsha indicated that bioluminescence has been adapted for other uses. “The chemicals can now be synthesized and are used in common glow sticks,” he said. “They also have several medical applications.” For example, because chemical luciferin reacts in such a noticeable way to ATP, Turpin noted that some scientists use it to detect bacteria, which also use ATP.
Indiana Department of Natural Resources (DNR) said on its website that the Say’s Firefly is one of the earliest emerging fireflies in Indiana. It may be seen from early May through mid-July. There are about 43 species of fireflies in Indiana. Of those species, 31 are lightningbug fireflies (those that flash). The others are called dark fireflies because they do not flash. More than 170 species of fireflies are found in the U.S.
The immature larvae are called “glowworms.” As their name implies, they glow, and unlike the adults, their lights stay on. Glowworms feed on soft-bodied insects, slugs, and snails. They are commonly found in damp areas, such as near ponds and streams. Speaking of firefly larvae, Xerces Society states, “Because of their large appetites and preference for snails and slugs, fireflies can be highly beneficial in gardens and agricultural settings.”
Incidentally, the reason we run the words “firefly” and “lightningbug” together (instead of each being two separate words) is that this insect is a beetle, neither a fly nor a bug. Turpin explained: “A scientifically correct common name would be ‘fire beetle’ or ‘lightning beetle,’ written as two words. Because the insect is not a fly – a member of the order Diptera – that common name is correctly written as the single word ‘firefly.’ It is also not a true bug in the order Hemiptera, thus ‘lightningbug’ would be the correct way to spell that name.” According to Turpin, about half of insect enthusiasts use the term firefly, and the other half prefer the term lightningbug.
Find original information from which I have sourced much of the above at Indiana DNR’s webpage, https://www.in.gov/dnr/entomology/resources-and-links/says-firefly/, and from Purdue’s Turpin at https5://www.purdue.edu/uns/html4ever/1998/980626.Turpin.fireflies.html.