Silent Sparks

Pyractomena Strangeness #3


“Tis strange – but true; for truth is always strange. Stranger than fiction.”

                               – Lord Byron, Don Juan (1823)

The previous episode left our Pyractomena larva hanging  – literally – doing some aerial pupation, very unusual behavior for a firefly! Forsaking the amphibious wanderings of its snail-eating childhood, the pupa now hangs quietly. But inside, a maelstrom of cellular reorganization and growth is transforming its larval body. In just a few weeks, it will emerge as an adult firefly. At this next stage, our Pyractomena will have only one thing on its mind: sex. And yup – you guessed it: Pyractomena fireflies have strange sexual habits, too!

Most male lightningbugs fly & flash to win females. But after racing to emerge early, Pyractomena borealis males forcibly mate with their child brides!

Males guard female pupae, then quickly mate with females as they emerge (photo from Faust 2012)

In late winter, when these larvae begin climbing trees to find good pupation sites, males begin to climb earlier than females. So males generally emerge into adulthood before females (a pattern known as protandry). But once these males emerge, they don’t fly off immediately in search of mates. Instead these day-active males crawl around the tree trunk, searching for female pupae. Lynn Faust discovered that males stand guard over these females-to-be, waiting patiently for up to 2 weeks. When the adult female emerges, the male mates with her  – completely bypassing courtship, without ever flying or flashing!

Yet these early-emerging males face fierce  competition. Up to half a dozen males may guard a single female pupa, piling on top of one another and fighting for position. Meanwhile, most Pyractomena females become child brides as soon as they emerge, while their wing covers are still soft and white.

Adult males and female have different lantern shapes (photo from Faust 2012)

It’s not until later in the season that Pyractomena borealis fireflies display like typical lightningbugs. When night-time temperatures warm up, males finally take flight. In early spring, you can see them flying high in the leafless treetops, giving quick yellowish flashes repeated every 2-3 seconds.

The first lightningbugs of the season have arrived! And they’re such a welcome sight, we can easily forgive all their strange behaviors.


Interested in Pyractomena‘s strange sexual habits? Check out these studies:
Erin Gentry, 2003. On sexual selection in Florida’s Pyractomena borealis. Florida Entomologist, Volume 86(2), pages 114-12.
Lynn Faust, 2012. Fireflies in the snow: Observations on two early-season arboreal fireflies. Lampyrid Volume 2, pages 48-71. (pdf available on ResearchGate)