Flashing Facts

Why Do Fireflies Flash?

All living creatures that sexually reproduce must attract a mate, and their mating behavior varies widely throughout the animal kingdom. For animals active in the dark, visual signals are not always possible, so they use other cues.
For instance:

  • Crickets sing.
  • Moths use pheromones — a kind of animal perfume.
  • Some spiders stomp their feet while others pluck the web threads. Daddy longlegs use touch.

Fireflies — at least the ones that flash — are unusual in that they have light-producing capabilities, making visual signals in the dark. Male fireflies flash while patrolling an area. If a female is impressed, she answers him by flashing from a perch, either on the ground or at some spot above ground, like a shrub.

It is up to the female to decide if she wants to mate with a particular male; if she doesn't respond to his flash, he cannot find her in the dark.

Playing the Field

How does the female decide which male to choose? During mating, the female firefly receives a "nuptial gift" from the male, which contains sperm to fertilize her eggs and food to help nourish them. Research on some species, including a local Photinus, suggests that the female is swayed by the brightness and duration of a male's flash. The more robust male firefly can produce a brighter flash and offer a larger nuptial gift, thus making him the preferred choice.

The mating ritual can also be a perilous process — learn more

Different Fireflies, Different Flashes

To most people, the flash of one firefly looks the same as another. However, with the possibility of many different species living in a meadow at the same time, each firefly needs a method of picking out his or her own kind.

Each species of firefly has a fairly distinctive flash pattern, which each differ in a number of ways:

  • Color
  • Length
  • Number of flashes
  • Interval of time between flashes
  • Time of night they are active
  • Flight pattern

Flashes can vary for a number of reasons, including temperature, time of night, time of year — and imitation.

Volunteer to share your observations of fireflies in your backyard — no special scientific training required.
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Fireflies can't see blue light, so you can safely observe them using a blue flashlight.

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