October 2014 Featured Paper

"Variation in the Flash Pattern of the Firefly Photuris versicolor quadrifulgens" by T. G. Forrest and Micky D. Eubanks. Journal of Insect Behavior, Volume 8, No. 1, 1995.
Read the Original Paper

Firefly flashes serve as mating signals. Male fireflies flash while flying over their territory, and interested females respond with a flash of their own. Each species of firefly has a precisely timed flash that distinguishes it from the flash of other species. In both Photinus and Pyractomena fireflies, the males produce only one pattern of flashes unique to their species, so their flash pattern can be used as a species identification tool. Identifying Photuris fireflies in this way is more problematic because they often utilize multiple flash patterns. The males may flash in a number of patterns when seeking a mate, or they may mimic the pattern of another firefly species altogether in order to elicit a response from a female Photuris that is hunting for firefly prey by imitating a female of this other species.

When seeking a mate, male Photuris versicolor quadrifulgens use five different flash patterns: a pattern of 2 to 5 pulses and a flicker. Little is known about these multiple signals and how they relate to finding a mate. This study intends to determine if the ratio of the patterns produced by the males changes:

  1. as the evening progresses,
  2. as the season progresses.

A study grid was set up in the field to monitor fireflies as they flew into the grid. The pattern of their second and third set of flashes while in the grid was recorded and graphed.

Results

The resulting percentage of occurrence of each flash pattern was as follows:


Flash Pattern: Rate of Occurrence:
3 pulses 66% of the time
4 pulses 26% of the time
2 pulses 6% of the time
Flickers 2% of the time
5 pulses less than 1% of the time

No significant change was detected in the percentage of pattern occurrence as the season progressed.

The percentage of pattern occurrence did change significantly throughout the night. As the night progressed, the number of flashes increased as follows:

  • Two-pulse patterns were produced within the first 20 minutes of activity
  • Three-pulse patterns were the most prevalent after 20 minutes, but dropped off rapidly towards the end of the evening
  • Four-pulse patterns were not produced until 35 minutes after activity began and increased throughout the rest of the evening.
  • All five-pulse flashes were produced during the last half of the activity period.
  • The flicker pattern was seen late in the evening and only during the early part of the season.

Twelve percent of the fireflies changed their pattern between the second and third set of flashes, changing equally between a higher pulse and lower pulse pattern.

It is not known if all male use multiple flash patterns. Possibly some use only a 3-pulse pattern, which was the most common pattern observed. To determine this, individual fireflies would need to be followed throughout the night.

DISCUSSION

One possible explanation for the males’ multiple flash patterns may be to conserve their energy. A two-pulse pattern presumably uses less energy than a pattern with more pulses. Early in the evening there may be fewer active females, and the effective range of the male’s flash is reduced by the ambient light of dusk. Expending more energy later in the evening when there is a better chance of finding a mate may therefore be to the male’s advantage.

Predation risk may be another factor in explaining these multiple flash patterns. Early in the evening when males in flight are more clearly visible, their flashing may attract predators. Fewer flashes decrease the chance of drawing a predator than would many flashes.

This study describes the variation in the flash patterns of P. v. quadrifulgens, but whether and how the female uses these signals is not yet known.


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