GAINESVILLE, Fla. — Butterflies may seem like the quietest of creatures, but a University of Florida researcher has uncovered new evidence that many of the colorful insects actually spend much of their time “talking” to each other.
UF researcher Mirian Hay-Roe found that blue-and-white longwing butterflies emit a barely audible series of clicks when they come into contact with other butterflies. The finding adds to a small but growing number of studies suggesting that some butterfly species use sound to communicate.
“It’s one of those accidental discoveries that sometimes happen in science,” said Hay-Roe, an entomologist at UF’s Institute of Food and Agricultural Sciences. “I wasn’t looking for communication in butterflies. I just noticed that these butterflies were making noise.”
Hay-Roe says she isn’t sure how the butterflies make the clicks. The blue-and-white longwing appears to have no specialized structure for making sound, she said. Future researchers are more likely to be interested in finding the insect’s “ears,” which butterfly experts say could be used as models for miniature microphones or improved hearing aids.
The blue-and-white longwing, also known by the scientific name Heliconius cydno, is a butterfly found in South and Central America. Adults of the species spend their days eating pollen from tropical flowers, and they congregate by the hundreds at night in trees.
Several years ago, Hay-Roe was working with a different species, and sharing greenhouse space with a researcher who was working with blue-and-white longwings, when she said she noticed something peculiar. The blue-and-white longwings seemed to be bullying her butterflies.
“They were chasing my butterflies all around the greenhouse,” she said.
Soon she noticed another odd thing: The longwings seemed to be making a faint clicking sound as they chased the rivals out of their territory. Further observation revealed the butterflies often made the sound when they encountered members of their own species. Longwings often clicked at each other during flight, when two of the butterflies were so close they almost touched. They also clicked at each other while roosting at night.
“When I told my fellow researchers that these butterflies were making noises, I think they thought I was going crazy,” Hay-Roe said. “The sound they make is very faint, but if you listen very closely you can hear it.”
Armed with a simple tape recorder and lots of patience, Hay-Roe captured some of the butterfly sounds on tape. She and co-author Richard Mankin, an entomologist with the U.S. Department of Agriculture, analyzed the sounds, publishing their results earlier this year in the Journal of Insect Behavior.
Hay-Roe said it will take further research to prove the sounds are a form of communication. But based on the context in which the sounds are made, she said, it is likely the butterflies are using the noise to shoo others out of their territory.
Butterfly talk has been an object of scientific speculation since Charles Darwin’s day. In 1874, the great biologist proposed that butterflies of another genus, Hamadryas, used clicking sounds to attract potential mates. Hamadryas species emit easily heard clicks, and they are often referred to as “cracker” butterflies.
Because Hamadryas butterflies make their sound when disturbed by other animals, some butterfly experts believe the noise is made simply to frighten predators. But a growing body of research in recent decades indicates the Hamadryas butterflies have ear-like organs that can detect clicks from other butterflies, strengthening the position that the sounds are a form of communication.
“No one has established beyond doubt that butterflies use sound to communicate, but we know that they can both make and hear the sounds, and that’s pretty good evidence for communication,” said Jayne Yack, an assistant professor of biology at Carleton University in Ottawa, Ontario. A specialist in insect neuroethology, Yack has done research on Hamadryas hearing systems.
The butterflies in Hay-Roe’s study may also have some sort of hearing mechanism. Hay-Roe cites a 1967 paper in which researchers found ear-like structures on the wings of Heliconius butterflies. The author of that paper proposed that longwings might use sound to communicate, but until Hay-Roe’s study, no one had recorded any sound from the butterfly.
Hay-Roe thinks she knows why: After a month in captivity the butterflies in her study went silent. Their offspring, born in a greenhouse, apparently never talked at all.
“One problem with greenhouses is that they’re often cooled with fans, which can make a lot of noise,” she said. “It’s possible that the butterflies simply couldn’t hear each other because of the fans and stopped making the noises. That might also explain why no one seems to have recorded this sound before.”
One of Hay-Roe’s butterfly recordings can be heard online at: http://cmave.usda.ufl.edu/~rmankin/soundlibrary.html#Heliconid. Click on “Heliconius cydno alithea” under the heading “Wing vibration sounds recorded in insect communication studies.”