So I began this post with a simple observation in my yard tonight. There are fireflies out and it’s raining. It’s not a hard rain, but it’s definitely raining. The fireflies (or lightning bugs) are still going at it, though, especially in the areas around the edges of my yard. They’re really quite persistent (or maybe just desperate for love). As I sat here pondering their search for a mate and the role of weather, I came across some other interesting information about these things. Before I get to the science, though, I have to share some musings on fireflies.
First of all, fireflies (or lightning bugs) are beetles. That makes them insects. And that’s exactly where things get wacky. I know a lot of people (my mother included) who hate insects and would never want one crawling on them, but fireflies (and ladybugs, I guess) seem immune to that kind of criticism. People are generally fascinated by them. Frankly, I have spent several evenings standing in place in my yard watching them. I think my neighbors find me a bit odd (‘That guy is just standing there in the dark again, Mabel.’ ‘Close the door, Frank.’).
It is this sort of fascination that makes people more appreciative of these fun insects and so, here comes the science. There are a number of studies looking at the timing of firefly displays around the world. Partly, this array of studies is driven by people’s excitement of them (and their willingness to travel places to see them. In the Great Smoky Mountains, predicting the firefly season was a project for researchers so that the National Park could give people notice about when the short firefly season there would likely get started.
Faust, L.F. and P.A. Weston. 2009. Degree-day prediction of adult emergence of Photinus carolinus (Coleoptera: Lampyridae). Environmental Entomology 38: 1505-1512.
Even more interesting is the amount of detail we know about some of the species of firefly (yes, there’s more than one species around here) and the amount of affection people have for them. Lynn Faust says in the conclusions for her paper (Faust, L.F. 2010. Natural history and flash repertoire of the synchronous firefly Photinus carolinus (Coleoptera: Lampyridae) in the Great Smoky Mountains National Park. Florida Entomologist 93: 208-217):
“No species can be properly conserved until it can be easily identified and its life history is known. After 18 years of studying Photinus carolinus and a lifetime of appreciating their display as a thing of magic and beauty, I am constantly humbled by how much remains to be learned about this tiny bright creature.”
If that statement doesn’t just encapsulate why some of us love nature and do science, well…it does get it. It’s a beautiful sentiment that really gets to the heart of what drives a field researcher. Nature is always fascinating and beautiful.
But to her other point, why are people worried about firefly conservation? Well, in part it boils down to the effects of humans. It’s not hunting (or even children with jars). This time it likely has to do with light. When people look at the factors that predict firefly activity, ambient light levels are the most important predictor (see studies above). While there is evidence for a circadian rhythm in these animals, that cycle is entrained (which means that it is influenced by factors in the external environment- light!).
Dreisig, H. 1975. Environmental control of the daily onset of luminescent activity in glowworms and fireflies (Coleoptera: Lampyridae). Oecologia 18: 85-99.
In some places, though, especially around human development, ambient levels of light are not dropping as much. Streetlights and neon signage keep light levels pretty high in some places and that turns out to be not-so-good for fireflies. An increase in development leads to a decrease in fireflies. Sigh.
Picchi, M.S., L. Avolio, L. Azzani, O. Brombin, and G. Camerini. 2013. Fireflies and land use in an urban landscape: the case of Luciola italica L. (Coleoptera: Lampyridae) in the city of Turin. Journal of Insect Conservation 17: 797-805.
In the end, I never did find a paper addressing changes in firefly behavior in the rain. There may still be something out there. I went down the typical internet path of (ooh, that’s cool, click on that link…). I did learn that, though they may not be quitters, I’m going to help the fireflies in my yard out by turning off my outside lights. Feel free to join me in the dark.