My new sister-in-law saw her first Firefly last week. They don’t have them in Nevada, but when she met my family her in Missouri, she was amazed. She asked what made them light up, why she didn’t grow up with them, etc. I remember, kind of, that Cecil answered these questions, but I can’t find the article. Any help would be appreciated! Thanks from Missouri!
I don’t know what makes them light up (although I suspect the same phosphorescence that other naturally glowing creatures utilize), but as for why they aren’t in Nevada, that can be answered with an educated guess.
Most insects are fairly sensitive to their environment, and have adapted to a certain average temperature, seasonal highs and lows, humidities, and even altitude.
It may be too dry or hot or too high above sea level in the area of Nevada where she grew up. Fireflies are plentiful here in New York’s Hudson Valley, but my wife, who grew up in Rochester, NY, hadn’t seen them before moving here. And we’re talking a difference of only 350 miles or so. Still, the temperature differences between the two areas may have been enough to cause fireflies to shun certain areas of Western NY. Goodness knows it’s true of termites and other insects.
In general, fireflies have two compounds, called luciferin and luciferase. When these two compunds combine (using the common energy coinage ATP), they produce another compound called luciferyl adenylate-luciferase. This compund, in the presence of molecular oxygen, will produce oxyluciferin, release luciferase and AMP (used energy coinage) and light.
That fireflies have control of their bioluminescence is apparent as you can communicate with them (if you know the language) with a small penlight. In one of David Attenborough’s nature specials, he knew if he waited a certain length of time after a flash appeared, then flashed his penlight for a certain length of time, he could lure male fireflies in to his hand (to their dismay, I’m sure, since Attenborough was imitating a female).
I too grew up where there were no fireflies (Southern California) and was mesmerized when I first saw their beautiful conversations. My sister-in-law said that they used to smear their bodies on their earlobes when kids to get “earrings.” 
howstuffworks has a good description:
How do fireflies light up ?
Reading the topic as Fireflys rather than fireflies, I was expecting a question about the Pontiac Firefly.
Or it could have been our own RTFirefly, although he’s not the sort of person who causes such trouble that someone would need help with him.
He’s really a very nice fellow.
Sadly, fireflies are all but gone from my area near Chicago. Pesticide use has killed them, development has destroyed their habitats and artifical lighting at night confuses an insect that evolved on the assumption it’d be the only thing glowing at night so this would be a good way of finding mates. Used to be a bunch of them when I was young, now 20 years or so later, I’ve seen one all summer. Oh well, enjoy them while you have them and hope you have them for a while
I’m in Chicago. My yard is full of them.
Thanks so much for the help! Using your info., I found a quote from a Purdue professor that said they didn’t exist west of the Great Divide, and that they like it warm and wet. That’s explains the lack of them in Las Vegas, where my sis-in-law lives. Or maybe they just can’t compete with Sigfreid and Roy.
Have a great Labor Day, and thanks again!