J Flash Guide

Looking for J-shaped Flashes

Can't see the video?

Watch an excerpt from Dr. Demary's Firefly Day 2010 presentation in which she explains this part of her research.

Firefly Watch began as a project focused on firefly activity in New England, but here's an opportunity for those of you in other areas, particularly in the mid-Atlantic states, to tell us more about what you're seeing.

You might have noticed a new question under "Focused Firefly Reporting" that asks whether the fireflies you saw were flashing while flying in a "J" shape. Your ability to identify fireflies by this distinctive flash pattern can help firefly researcher Kristian Demary in her studies on the effects of ambient light on fireflies.

Identifying this species — called Photinus pyralis — will aid Dr. Demary in determining whether dusk-active fireflies are coming out during the dark-active period, when street light simulates natural light of the dusk hour.

j-shaped flash pattern of P. pyralis

Photinus pyralis is very common in and around the mid-Atlantic region and is active primarily around dusk. Here's what to look for:


  • The male P. pyralis flies in an "S"-shaped path, flashing while in an upward turn to form a "J."
  • The male makes this flash about every 6 seconds.
  • From the ground, the female responds with a flash every 2 - 2.5 seconds.


We've made our full data set available online, and you're invited to interpret it.
:: Learn More
Observing fireflies is a great summer activity. Join our network of volunteers and track your sightings throughout the season.
:: Sign Up
Pick a location, observe it weekly, and use our online tools to follow your progress.
:: Read More


Fireflies can't see blue light, so you can safely observe them using a blue flashlight.

- Get More Tips