From Joanne, in Wisconsin –

About 15 years ago we held a family reunion near a small lake in the Blue Ridge Mountains, near Saluda, NC.  It was around July 4th, so around the lake lots of people were setting off fireworks.  We were gathered by the lake near a wide grassy area that led right up to the base of the mountain. That night the fireflies appeared around dusk, just when the fireworks started. Although the fireworks were going off much higher up, we realized that down below the fireflies’ flashing was gradually getting synched up with the fireworks. As it got darker, the coordination seemed to increase so that every time a firework went off, the fireflies would light up, all pretty much at the same time.

It was a magical scene – a constellation of yellow-green flashes lighting up down near the ground, triggered by the dramatic firework explosions in the sky. And the fireflies earned much bigger “ooooohs!” than the fireworks! Only later did I learn that what we were seeing were probably the romantic signals of male Photinus carolinus fireflies, flashing together like one big mega-male to try to win the favor of their females.