December 2013 Featured Paper

"Reproductive Ecology of Two Species of Photinus Fireflies" by Sara M. Lewis and Ona T. Wang. Psyche, 98: 293-307 (1991).
Read the Original Paper

The flash mating signals of fireflies have been well documented, but little is known of their mating behavior. This study reports on the mating behavior of two grassland species of Photinus: P. aquilonius and P. marginellus. Both of these species have long-lived females that mate multiple times throughout their adult lives. Both also show a marked seasonal shift in male to female ratio as the season progresses.

The chart below compares many mating aspects of the two fireflies.

Behavior P. aquilonius P. marginellus
Flight time Begins 20 minutes after sunset
For 1 hour
Begins 10 minutes after sunset
For 40 minutes
Flight season (at study site in MA) Late June to late July Early July to late August
Flight path Up to 12 feet above ground Less than 6 feet above ground
Habitat Open fields bordered by woods Mowed grass under grove of trees
Male flash Single flash repeated every 5-7 seconds at 70 deg. Single flash repeated every 3-4 seconds at 70 deg.
Female response 2 second delay at 62 deg. 1 second delay at 62 deg.
Males approach Land within 1.5 feet of female and walk towards her Males took to flight if they couldn’t find females
Female perch Grass or small shrub Mown grass, but moves to tree canopy later in season if unsuccessful
Mating stage 1 with male on top Up to 1 hour Up to 25 minutes
Mating stage 2 with male and female back to back Up to 8 hours Up to 3 hours
Elapsed time to last resighting of marked males 4 days 11 days
Elapsed time to last resighting of marked females 21 days 41 days

Early in the season, males outnumbered the females. Often, multiple males were seen signaling to a single female, but the first to reach her usually succeeded in mating. Other males were observed trying to dislodge this male, but none were successful. As the season progressed, the number of males declined while female numbers remained constant, until by the end of the season, multiple females vied for the attention of the few remaining males.

Two possible reasons are suggested for the extended mating time in both species. Along with sperm, males transfer a protein mass called a nuptial gift to the female. Possibly this transfer takes time. Another explanation may be mate guarding, where the male occupies the female throughout the evening to prevent her from mating with other males.

In both species, males were seen repeatedly inserting their reproductive organ into the female. Several times, a drop of liquid was observed on the tip of the male reproductive organ upon withdrawal from the female. The purpose of this is not understood, although possibly the male is removing sperm from a prior mating.

Since males are active fliers, they are more likely to be caught in spider webs. This may be a factor in male numbers declining throughout the season while female numbers remain fairly constant.

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