If you’ve been paying some attention, you probably already know that here in North America, we’ve got several different kinds of lightningbug fireflies. Those in the genera Photinus and Photuris are common and relatively well-studied. But the Pyractomena lightningbugs – also pretty common – are a black box. We know so little about them! And more’s the pity because Pyractomena have a pretty bizarre lifestyle, making them quite a bit different from our other fireflies.
So here’s the first taste of Pyractomena strangeness: these amphibious larvae are snail-eaters!
During their juvenile, or larval, stage, all fireflies are voracious predators. The young of other North American fireflies hunt their prey in soil or leaf litter. But Pyractomena adults often live in marshy places, so that’s where the females lay their eggs and where young Pyractomena grow up.
Pyractomena larvae are amphibious, and stalk their prey both under and above water. Climbing around on emergent plants, these larvae search for snails and other aquatic creatures – their diet also includes leeches, damselfly nymphs, and limpets. Once the larva captures a snail, it drags its prey out of the water by walking backwards. Sticking its pointy head inside the shell, the larva begins tearing into the snail with its sharp jaws. Their remarkably extensible heads let them to reach the inner recesses of the snail’s shell – good to the last drop!
When tested, some Pyractomena larvae survived for up to 31 days completely submerged underwater! Although Pyractomena larvae don’t have gills (as the fully aquatic larvae of some Asian fireflies do), they apparently can absorb oxygen right through their skin.
As it eats and grows, the Pyractomena larva molts through several larval instars. Once it has grown big enough, it will need a safe place to pupate. And of course its Pyractomena strangeness continues, so stay tuned for the next episode of Stranger Things – The Firefly Version!
(For more details on these strange larval habits, check out this study by Larry Buschman, Biology of the firefly Pyractomena lucifera, published in 1984 in Florida Entomologist.)