Autumn happens to be quite an exciting time for fireflies. I get it – you probably can’t imagine fireflies beyond summer. And that is when adult get all reproductive and stuff. But there’s cryptic chapter in the firefly’s life story, and it’s starting right now.
Once mated, the female firefly will produce 30-100 eggs, laying them one-by-one in some moist dirt or moss. After a few weeks, these eggs hatch out into tiny larvae that immediately burrow down underground. Though adult fireflies only live a few weeks, their progeny will spend up to two years hanging out underground.
Baby fireflies happen to be voracious predators. They’re constantly on the hunt for earthworms, snails, and any other soft-bodied prey. They attack creatures that are much bigger than themselves. How do they manage this? First, they use their sharp, sickle-shaped jaws to inject the prey with paralyzing neurotoxins. Next, they secrete digestive enzymes to liquify their prey, then they slurp it up. Earthworm smoothie, anyone?
When they’re disturbed, larval fireflies glow from two tiny lanterns located at the tip of their abdomen. All firefly larvae can light up, across 2000+ species, even when the corresponding adults cannot. So we think fireflies’ light-producing talent first evolved because it gave these juveniles some advantage.
But … what’s the point of these juveniles being so conspicuous?
We know that fireflies contain nasty-tasting chemicals that help them avoid getting eaten (see earlier post). Lots of poisonous creatures use bright coloration to warn off potential predators. Yet firefly larvae are mainly active at night or underground, where having bright colors would be futile. But a flash in the darkness would certainly do the trick – like a neon sign, it blazes out “I’m toxic – stay away!”
So get ready to watch for firefly larvae crawling along roadsides and wooded paths, glowing dimly. Often overlooked, these juveniles should rightly be celebrated as the original inventors of fireflies’ magical lights.