Northern Woodlands Magazine

are all courting a single female, sometimes one male will slyly give a pseudo-female flash in response to a rival male. Looking just like a female flash, the male’s pseudo-female flash crescendos, then slowly fades out; he also flashes using the female’s typical response delay. Based on my own experience trying to locate females, I know these transsexual flashes can be pretty convincing. It appears these males have figured out a clever way to decoy competitors away from the real females.

Even though they lack overt weaponry, competition among
male fireflies sometimes gets physical. In Photinus pyralis, the
Big Dipper firefly, sometimes as many as 20 rival males will
surround a single female, creating a writhing love knot. Males
vigorously push and shove each other, using their head shields
to dislodge their rivals. Eventually one male wins out and mates
with the female, although what exactly makes a male victorious
in these battles isn’t yet known. Poor losers or ever hopeful,
several of the losing males often pile on top of the happy couple,
stacking themselves up to six deep. Perhaps this is why male
Pteroptyx (“bent-winged”) fireflies from southeast Asia use
their wing covers to tightly clamp around their mate’s abdomen
– it seems a good way to prevent hostile takeovers.

Seen through the lens of sexual selection, we now have an entirely different view of the lovely luminous display out here in this meadow. It stars hundreds of male fireflies flying and flashing their hearts out in a quest for genetic survival. Male fireflies spend night after night flash-competing with scores of rivals to locate scarce females. These nocturnal flights require a lot of energy and are fueled only by whatever the male has managed to store up during his larval feasting. And as we’ve seen, flight isn’t the only courtship expense incurred by males; their search missions are also fraught with dangerous predators. In fireflies, courtship is definitely a big-ticket affair, and the cost rests squarely on the males’ shoulders.

Sara Lewis is a professor in the Department of Biology at Tufts University. This piece was adapted with permission from her book Silent Sparks: The Wondrous World of Fireflies, published by Princeton University Press in 2016.