September 2009 Featured Paper

"Flashes of Photuris Fireflies: Their Value and Use in Recognition" by Dr. James Lloyd, Department of Entomology and Nematology, University of Florida, Gainesville, 1969
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Synopsis

This paper presents Dr. Lloyd's observations that have a bearing on using firefly flashes to recognize firefly species in the genus Photuris. Unlike Photinus fireflies, which seldom flash except for mating, have distinct flashing behavior, and will flash in captivity, Photuris flashing proves rather difficult to measure. The paper discusses some limitations in using Photuris mating signals for species identification, and why it is difficult to both recognize a Photuris mating signal and identify which part of the flash is important in species recognition.

The mating flashes and behavior of Photuris fireflies are difficult to recognize and analyze for the following reasons:

It is difficult to recognize their mating signals.

  1. Flashes are emitted for reasons other than mating.

    Some female Photuris can mimic a number of other fireflies in the genus Photuris, Photinus, and Pyractomena. These flashes can be very different than their mating flash, and in the face of imitating Photinus, the females lure the males over in order to eat them.

    When landing, walking, or before takeoff, both Photuris males and females use their flashes for illumination to help them see predators, vegetation or puddles. It is doubtful that these flashes are used in mating since they do not attract other fireflies.

    Photuris fireflies may flash when handled, knocked to the ground, or confined.

  2. Signals change in flying males.
    In one species studied by Dr. Lloyd, males displayed three different flash patterns. Their flash lengths gradually decreased over the course of the evening, resulting in three different observations. Without adequate scrutiny, one might view this as three different species of fireflies.

It is difficult to identify and experimentally determine the elements of Photuris mating signals that convey species information.

  1. Signals are structurally complex.
    Because of the complexity of some male Photuris flashes, the functional unit of the flash that females respond to is difficult for researchers to recognize. The flash in the signal of some males may consist of multiple flashes or components of different brightness that may occur too rapidly for the eye to detect, and they can also vary according to air temperature or the firefly's speed.
  2. Captive females are not responsive to male flash imitation.
    The female response to a male's flash is an integral part of the flash code of a firefly. This is often determined using captive females responding to a male flash or an artificial flash. However, female Photuris fireflies don't respond in captivity.
  3. Fireflies mate in inaccessible places.
    Many species of Photuris fireflies live in the canopy of trees and flash and mate near the tips of the branches. It is almost impossible to study the flash patterns of these fireflies as one would the fireflies that live on or near the ground.

As a guide to identifying firefly species, mating flashes have their limitations in the genus Photuris. It cannot be assumed that two Photuris fireflies that live in different geographical areas and have the same flash pattern are the same species. Also, since fireflies have a two-year life cycle, it cannot be assumed that adult Photuris fireflies seen in consecutive years are the same species. In each case, the fireflies and their flashes must be analyzed to make identification certain, and one must not rely on the flash patterns alone.


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