London: Male fireflies that try to attract mates with a flash of light also seduce the females with a gift -- a spermatophore package or a capsule containing sperm and nourishment for the female.
Researchers from Tufts University in Boston, US, found that females preferred males that had the largest, most nourishing gift, BBC reported. The team presented their findings at the First Joint Congress on Evolutionary Biology in Ottawa, Canada.
Sara Lewis, who has been studying fireflies for 20 years, and Adam South used LED lights to mimic the flashes of "amorous" male fireflies, the report said.
The scientists showed one group of females the artificial male flashes in patterns and durations that had been proven attractive in previous studies.
Another group of females saw "unattractive" flashes.
In the wild, females are very "picky" about which males they reveal themselves to during the courtship. Females only "flash back" to males they are attracted to.
In the experimental set-up, after several minutes of the courtship flashing, males and females were paired together in miniature chambers.
The scientists filmed the incident under infrared illumination to see what was happening when the lights went out.
The video footage revealed that females were more likely to mate with males that had larger nuptial gifts to offer.
Once the males and females were together, the quality of the flashes did not seem to affect the outcome of their meeting.
However, since the spermatophore is transferred internally, it was not clear how the female uses the size of this gift to decide whether to mate with a male.
South said "attractive flashes only seem to benefit males during the early stages of firefly courtship".
"Initially, flashes are important. But once males make physical contact, females switch to the alternative cue," he said.
"If we had stopped studying the mating habits of fireflies after the flashing stopped, we would have missed this amazingly complex and incredible story," he said.
Other insects that accept gifts are female Paratrechalea ornata spiders that receive food parcels wrapped in perfumed silk from suitors, while the male fruit-fly or Drosophila subobscura regurgitates a nutritional soup for its female.