Each year, early in the summer, the flashing lights of the season’s first fireflies lure thousands of children from their houses. Running this way and that, the children try to capture the twinkling insects in an empty jar. Its a ritual that has gone on for generations.
As you probably already know, only the male firefly can fly, and he is the one you see darting back and forth across your lawn, flashing his courtship message to the wingless female who waits in the grass or shrubs below. What you may not know is that there are several different species of firefly, each with its own flash pattern that may differ in color, intensity, or timing of the light. In fact, individual species can differ even in the time of night and altitude at which they flash. In the mating game of fireflies, the male s flash must be exactly right in every way or the female will not respond.
One of the most common fireflies is Photinus pyralis (there are no common names for the different firefly species), and early each summer evening you can find this insect flashing its light above the open fields and lawns of eastern North America. The signal of this firefly is recognizable because it always rises upward as it flashes its bright, yellow light. This rising pattern is formed because Photinus pyralis always flies in an undulating manner and flashes only while it is ascending. At sunset, this firefly flashes low to the ground, but as the evening wears on, it will soar somewhat higher, continuing to emit its identifying J-shaped flashes.
The actual flash code of Photinus pyralis is quite simple and is based on the time that elapses between the male’s burst of light and the female's response. While flying, the male gives off a series of flashes about six seconds apart. The female, who is located down in the grass, will then flash a response about two seconds after the male’s signal. When the male sees this, he flies toward the female, and the two continue this sequence of flashes until they are together.
You can join this "romantic" conversation and lure a male Photinus Pyralis to your hand by imitating the luminous response of a female. All you need to do is take a small flashlight and go to a place where you see the J-shaped flashes of this firefly. As soon as you spot one of the flashes, start counting off two seconds (one Mississippi... two Mississippi), and then, holding the flashlight close to the ground, turn it on for about one second. Almost immediately, the male will turn and head toward your light. When he flashes again, give him another quick flash of your light after waiting the proper two seconds. Continue this responsive flashing, and the firefly will keep moving closer. As it nears you, its flashes will become much weaker. Keep flashing your light and in no time at all, the male will land directly on your hand or nearby and walk to your light.
If you have only a large flashlight, you can still Perform this trick by keeping the lens of the light almost flat on the ground. When you see the male flashing, tilt your light up a little on the side that faces him and give it a flash. He will come in.
I have brought in male Photinus pyralis from over 40 feet away, and it can quickly become a neighborhood fad. However, make sure you remind everyone that the flashlights should be put away when they finish using them. More than once I have found my light in the grass as I left for work in the morning.
(Excerpted from Talking to Fireflies, Shrinking the Moon. Fulcrum Publishing, 1997.)
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