We can sense the change all around us – Earth’s climate is shifting. Our summers are getting hotter, and precipitation patterns are getting more extreme. But climate change doesn’t just affect human beings. It’s a game-changer for all of Earth’s living things. So maybe you’re wondering – how will fireflies react to such fundamental changes?
Everyone knows Earth’s temperature is rising. You’ve probably noticed that many flowers have now started to bloom earlier. So it’s not surprising that fireflies may also start “flowering” earlier. Like many seasonal creatures, fireflies depend on local soil and air temperatures for cues about when to emerge. With warmer temperatures, firefly eggs and larvae can grow more quickly and so will become breeding adults sooner. This already seems to be happening in at least one firefly species.
Over the past 20 years, naturalist Lynn Faust has kept track of exactly when the synchronous fireflies of the Great Smoky Mountains emerge. (This particular species, Photinus carolinus, happens to be pretty noticeable, and their spectacular light show attracts thousands of tourists each year). And Faust’s records show that their peak display is trending about a week earlier now, despite some year-to-year fluctuations.
The U.S. currently hosts more than 120 different firefly species, with the greatest biodiversity occurring in southeastern states. But Canada has only about 25 firefly species. As global temperatures rise, the geographic range of many firefly species may be shifting farther northwards – good news for firefly lovers in Canada!
Lights across the water
What about changing precipitation patterns (both rain and snow)? Rising global temperature leads to more moisture in Earth’s atmosphere, which means increased precipitation. But, as we know from news reports, this precipitation doesn’t fall evenly back to Earth. During the summer of 2016, rainfall extremes caused widespread drought or flooding in different parts of the U.S.
We know that fireflies thrive best in moist habitats, as I’ve described elsewhere in this blog. In the U.S., juvenile fireflies live in soil or rotting wood, and they can spend up to two years in this larval stage. But because firefly eggs and larvae require moist conditions, they’re quite sensitive to rainfall patterns. As a result, fireflies likely won’t be able to survive in places that suffer from long periods of extensive drought.
Heavy rains, on the other hand, could be beneficial for firefly populations. Wet and warm conditions should increase the growth and survival of juvenile fireflies. Apparently, this is exactly what happened during 2016 in central Texas. After an unusually wet spring, Texans enjoyed a bumper crop of fireflies. Summer also turned out to be atypically wet, which created a second wave of fireflies that blossomed in September, lighting up backyards and parks as late as October!
Such unusually wet and warm weather seems to have act like an incubator for a second firefly generation; these fall-emerging adults were hatched from eggs laid the previous spring, and managed to grow quickly enough to become adults in just a few months.
So how will fireflies react to climate change? From their perspective, there seems to be reason for optimism. But the truth is, we really don’t know. We’re caught in the midst of an Earth-sized experiment. As temperatures rise and rain patterns shift, it will surely be a different world for fireflies, just like for the rest of us.