There are a few different ways to determine the sex of a firefly. The simplest way is to observe whether they are flashing while flying or while resting on vegetation. Typically, the males flash in flight while they are patrolling an area for females. The females observe from their perch and, if interested, they return the males' flashes.
Although looking for flashes from fireflies on a perch or in flight is a good general rule for identifying the sex of a firefly, it is not totally reliable. Males often begin the evening by flashing from a perch before taking flight after sunset, and when they later land to find a female, they continue to flash. In addition, Photuris females often flash while in flight.
A more reliable method is to look at the light organs of the firefly. To do this, examine the firefly closely and carefully. If it is in flight, then you must catch it. Fireflies can be easily damaged by rough handling – learn more about how to handle a firefly.
For Photinus and Pyractomena fireflies, it is easy to determine their gender by examining their light organs. A male Photinus can be identified by the last two light sections on his abdomen, while a female has her light organ on the second-to-last segment.
In Pyractomena, the male's light organ is similar to that of Photinus, but in the female, the last two segments have two small light organs, one on each side of the segment.
Identifying male and female Photuris fireflies is more difficult since both have light organs on the last two body segments. However, on the female, the area that produces light does not cover the entire segment and is bordered by a translucent margin. With some practice, you can pick out this subtle difference.
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