3 - 5
15 min - 1 hr
If you’re lucky enough to live where fireflies flash at night, then you have surely seen their magical illuminations on warm summer evenings. But did you know that by observing fireflies while they are flashing, you can learn to communicate with them? If you haven’t already, watch the Science Friday Video “In a Flash: Firefly Communication” for a little background on how fireflies use light to communicate:
By watching and comparing fireflies all across the country, scientists have been able to map out the unique flash patterns of male and female fireflies of different species. Dr. John E. Lloyd, an entomologist at the University of Florida, featured in the video above, was one of the first to do this extensively for North American species of firefly in the genus Photinus.
Using just a penlight and this photinus firefly flash signal cheat sheet based on Dr. Lloyd’s observations, you’ll be on your way towards speaking in a genuine firefly dialect (though your accent may need extra work).
Key: (1) Photinus consimilis (slow pulse), (2) Photinus brimleyi, (3) Photinus consimilis (fast pulse) and Photinus carolinus (4) Photinus collustrans, (5) Photinus marginellus, (6) Photinus consanguineous, (7) Photinus ignites, (8) Photinus pyralis, and (9) Photinus granulatus
Materials and Preparation
- Pen light, small key ring LED light, or other small light source
- Some electrical tape or opaque tape
- Photinus Firefly Flash Signal Cheat Sheet
Use a piece of the electrical tape to cover the edges of the flashlight so that only a sliver of light (2-3-millimeters) shows when you turn it on.
Male Firefly Flash Patterns
Male flash patterns are longer and much more elaborate than females’, and they are usually the first ones observed on a summer evening. Go outside just before dusk to an area where you have seen fireflies display before, and bring your modified penlight. Using your light, try to recreate each of the male firefly flash patterns described below. Pay attention to the length of each flash and the amount of time between each flash. You can approximate the proper timing of your own flashes by counting seconds as you go. Periodically stop and observe the bushes and grass around you, where female fireflies might be located. If your flashes match the flash patterns of nearby females of the same species, they will respond to you with a brief response flash.
North American Male Photinus Flash Patterns
(From Lloyd 1966, modified for clarity and used with permission, illustrations by A. Zych):
- Photinus pyralis
The flight path of P. pyralis is vertically looping, with a single long flash on the forward and upward portion of each loop, resulting in a “J” pattern.
- Photinus macdermotti
Males fly straight, level, and slowly, 1-5 meters above the ground. They emit two slow flashes every 1-2 meters or every 2 seconds, flying upward on the second flash.
- Photinus consanguineous
Males fly straight and slowly, bobbing up every 0.5 meters or so. They emit short (0.7 seconds) flashes at the start and end of each jump in their flight path.
- Photinus marginellus
The flight path for P. marginellus entails hopping up and down low in the brush, with a short, 0.5-second flash at the end of each “hop.” Flashes are about 3 seconds apart.
- Photinus brimleyi
Photinus brimleyi fly rapidly in straight or loosely meandering paths at a constant height. While flying forward, they begin to flash, and then during light emission, they stop suddenly and hover for a moment before extinguishing their light and rushing forward again. This creates the appearance of a jagged flight path.
- Photinus collustrans
Males alternate between flying straight and flying in a lateral arch or in a sideways loop (as though dodging an obstacle). They flash during each lateral deviation from their straight path for about 0.4 seconds per flash.
- Photinus granulatus
This species flies about 1 meter off of the ground, flashing every other second while jerking back and forth to create zigzag patterns.
- Photinus ignitus
Males fly straight, level, and slowly, about 1-2 meters above the ground, emitting brief (0.2 seconds) flashes without changing speed. Flashes occur every 5.1 seconds.
- Photinus consimilis
These males flash late into the evening. They fly slowly, emitting 4-9 quick flashes every 10 seconds, sometimes stopping and hovering on the last flash. They may also produce 2-3 slow flashes, emitted during level flight every 2-6 seconds.
- Photinus carolinus
The flashes of this species are very similar to the flashes of P. consimilis, with a slightly longer interval between sets of flashes of about 13 seconds.
Decode Female Firefly Flash Responses
In Science Friday’s interview with Dr. Mark Branham, the University of Florida entomologist shared a fun little trick for mimicking females:
If you watch long enough, you can see females in the grass respond to a flying male, and then you can see firsthand what the appropriate timing parameters are of that female flash pattern and how long after the male flash they are responding. If you just mimic that, you can call in lots of fireflies, and they’ll come right to you—and they’ll even land in your hand.
As you observe the flashes of male fireflies, also look for female flash responses. How long do they wait to respond, and how many flashes do they respond with? Try mimicking this wait-flash behavior, and see how many males you can attract. How do the intensity, rate, and height at which you flash your penlight affect how many males you attract? Is there any evidence that there is more than one species of firefly flashing around you? How can you tell?
Make It a Game
Got a group of campers and some flashlights? Take turns mimicking the flash signals of species of Photinus firefly while other campers try to guess which species they are mimicking using the Photinus signal cheat sheet. Have campers buddy-up to create their own unique flash code to signal their identity to one another, and have others try to crack the code by observing them.