June 26, 1996
Marc A. Branham's report on "Female fireflies prefer rapidly flashing males" appears in the June 27 issue of Nature magazine. British Broadcasting Company has also filmed his research for inclusion in a "Beetlemania" segment for its "Nature" series.
"We know how fireflies flashed, the biomechanics of it, but we didn't know why they flashed," said Branham.
"In almost all the species in the United States, the males fly around while they flash. The females sit on the ground in the high grass and they only flash at certain males. It's pretty obvious, once you start to watch the females, that they don't flash back at just any male that happens along," he noted. "The question I had was if female fireflies actually chose males based on their flash patterns."
To find out, Branham selected a species of firefly, Photinus consimilis, in which the males hover in flight while flashing. "There is one species where the males fly in a `J' pattern but that would be hard to emulate mechanically. I needed one where I could replicate the flashing."
While Kansas has 15 species of fireflies, one of the nearest areas offering a large population of Photinus consimilis is Roaring River State Park, in southwest Missouri. Branham spent the summer of 1993 videotaping firefly signals for analysis and the summer of 1994 conducting research at the park.
Branham analyzed the videotapes to determine the average flash pattern based on different temperatures, since fireflies flash more quickly at warmer temperatures. He also analyzed light intensity and different colors.
Then Branham created an artificial firefly with help from Jonathan E. Mericle, a systems specialist with the KU chemistry department's instrumentation-design laboratory.
The key component to the fake firefly is a light-emitting diode driven by a computer that could adjust for flash speed and light intensity. Mericle helped Branham adapt a software program used to analyze insects' audio patterns to a program that could analyze the flash patterns and create different flash patterns to test the fireflies' response.
However, the only thing that made a real impact on the females was the rate of the male flashes.
"Not only did the females prefer the faster flashing males, they really preferred males who were faster than the average male in the population. Some of the females would flash back to those mediocre males who were just around average but the really slow flashers didn't get the time of day," Branham said.
"In the species I was working on, I found out if a female kind of likes a male, she will give one semi-bright flash. If she really, really likes a male, she will give up to 12 pulses that are really bright. That is like the difference from whispering to yelling `Hey, I'm right here! Come on down and land!' "
Branham explains that after the female flashes back, there is a short flash dialogue between the male and female until the male can get a good fix on her position to land. "If the females don't flash, the males don't even know they are there."
Some males don't play by the rules. "There are male fireflies who will spot a dialogue in progress, and they're better at finding females that are on the ground then the male that is signaling. They'll just beeline on down there and try to cheat."
Branham said he hit on a flash pattern that was guaranteed to attract females. The pattern was much faster than what would occur in nature but "I got very good at it. I could even take the act to Las Vegas."
All of the fieldwork had to be conducted at night with no artificial light, so Branham spent hours nightly with the artificial firefly, out along riverbeds in the state park. He indicated that years of camping and Boy Scout experience helped him handle the difficult research situations.
"I had to contend with floods and tornadoes," Branham said. In fact, right after the BBC crew arrived to film him conducting his research, there was a tornado nearby and then a flood wiped out the fireflies for about two weeks. "They hung in there until they could get the shots they needed."
In addition to field work, Branham would capture female fireflies for controlled experiments that he set up in the cabin where he was staying. He also conducted some experiments setting up his artificial firefly as a female. "The males would come down, but then they seemed to be pretty unhappy when they found out it wasn't a real female firefly."
Branham received a master's degree in entomology from KU in 1995. He has been accepted into a doctoral program this fall at Ohio State University, Columbus, where he plans to continue his firefly research. Michael Greenfield, KU professor of entomology, is the co-author of the article and was Branham's adviser on the research project. Branham's other academic adviser was James S. Ashe, professor of entomology and director of KU's entomology museum.
Grants from the American Museum of Natural History, the KU Museum of Natural History and Sigma Xi, a scientific research society, funded Branham's KU research.
Story by Kay Albright, (785)864-8858