May 2010 Featured Paper

"Flight Studies on the Photic Communication by the Firefly Photinus pyralis" by James Case, Marine Science Institute, University of California Santa Barbara, Integrative Comparative Biology, June 2004.
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Synopsis

The priority of this study was to test a flight simulator that studies male communication in Photinus pyralis. The study includes details on male courtship flight, as well as flashing behavior in flying females.

Flight Apparatus

A small piece of balsa wood was glued to the thorax of a firefly. The balsa was then attached to a wire apparatus that could record the direction of flight of the firefly. The firefly could fly in place, with a stream of air passing by the firefly to simulate forward motion. The recorder allowed the firefly to turn in any direction, but it did not allow the firefly to move up or down.

Light-emitting diode (LED) lights were placed on either side of the firefly to simulate a female response to his flashing. In a typical experiment, the firefly flew spontaneously or, with a brief air puff for encouragement, it flew in a steady flight into the wind.

Results

In the study, the firefly's leg and antenna position were identical to those seen in the field. During flight, the firefly raised and pulled its legs toward its body, rarely moving until landing. Holding its body in an upright position, the firefly extended its antennae forward.

While "patrolling" or looking for a female, the male Photinus pyralis typically flashes while flying in an upward swooping flight path, creating a "J" pattern of light. Although the flight apparatus prohibited upward or downward flight, the firefly's wing strokes did change in what was assumed to be the proper position for a firefly changing height.

In another type of flight pattern — "male to male interactions" where the flight normally would be level — the wing strokes did not change.

Flight Orientation of the Male

Before receiving a flash response from a female, a flying male frequently turns his head from side to side. When he spotted a response flash from an LED female, the male's gaze immediately shifted toward the light source, with his abdomen often twisting to face it. The male's second flash was invariably given with his head and body directed toward the light source.

Male-male Interactions

In the wild, males often respond to each other by flashing about 0.4 seconds after the flash of another male. With a number of males interacting with each other, this can produce a crude synchrony of male flashes. This male-male interaction does not involve a turning of the head toward other flashing males. Male-male interactions were readily triggered in the flight apparatus.

Female Flight Behavior

Female fireflies readily flew in the flight chamber. They responded to male LED male flashes with the properly timed two-second return flash. Remarkably, these flying females also emitted an extra flash, about 0.4 seconds after the male flash — thus giving a double flash in response to the male — one after a 0.4 second delay and another after the expected 2 second delay. This early flash has never been seen in wild fireflies.

Photic Noise and the Female Response

While perched or flying, a female tended to aim her flash in the direction of the male's flash. However, the female was easily dissuaded from responding to a male by another flash from a different direction, as long as it wasn't nearly simultaneously timed with the first flash. In nature, we can assume that communication is frequently disrupted between females and males that are not synchronously flashing.

Discussion

Adequacy of the Flight Apparatus

The value of the apparatus data is limited by the lack of a changing background as the firefly flies forward. Also possibly impacting the value of the apparatus is the fact that as the male flies toward a LED, he gets no closer. Still, males were often seen flying towards a fixed light for considerable periods of time.

Visual Searching

Because the firefly's eyes are so large and can receive a signal from many directions, the question arises as to why the male turns his head while searching for a female. With such large eyes, a firefly is assumed to have an area of overlapping vision between the two eyes, suggesting a binocular vision that may help the firefly navigate around vegetation in his approach to the female. However, if this is true, then the question arises as to why male fireflies often have difficulty finding the female once he has landed nearby.


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