Scientists investigate fly swarms

Researchers have found a mechanism to analyze fly swarms, which may provide valuable insight into the structure of animal collectives from bird flocks to human crowds.

Two researchers — one from Yale and the other from the Massachusetts Institute of Technology — joined forces and used their backgrounds in engineering to evaluate the structure of fly swarms. With high-speed cameras, they recorded swarms and analyzed the behavior of individual flies as well as the collective motion of the group. The researchers said they hope their findings, which were published Jan. 15 in the journal Scientific Reports, will lead to greater understanding of other species’ forms of collective motion.

“There’s been a lot of work done on qualitative observations about insect swarms,” said Yale School of Engineering & Applied Science professor Nicholas Ouellette. “What’s been missing is the empirical quantitative research on the swarms.”

Ouellette and Douglas H. Kelley, an engineering postdoctoral associate at MIT, decided to analyze the structure of swarms because they noticed a dearth of information in the field of entomology, the study of insects. Previous research on the subject had focused only on qualitative descriptions of swarms — such as their size — and had not asked detailed questions about individual flies’ behavior within the group.

Ouellette and Kelley used synchronized high-speed cameras to record the fly swarm, and then used a custom computer code to analyze each frame of the film. By studying individual frames, they were able to track the motion of each fly in the swarm. The tools they employed to film the flies are typically used for measuring fluid flows, but they discovered that because their software was designed to understand the motion of small particles, it could be used for insects just as easily as for liquid.

“We had done work with 3-D high-speed tracking, and we realized we had all the experimental tools we needed to track the swarms,” Kelley said.

When analyzing the swarms, they discovered that individual insects tend to fly faster horizontally. Ouellette said they discovered that swarms are highly structured, and comprised of many small groups of flies. The flies tend to move toward the center of the swarm, giving the appearance that there is a force holding them together.

Initially, Ouellette and Kelley encountered challenges in creating sufficiently clear recordings of the swarms. Kelley said the researchers learned that the flies preferred to swarm at dusk, so they had to backlight the film with red lights in order to view the flies clearly.

James Puckett, a mechanical engineering postdoctoral associate at Yale who recently joined Ouellette and Kelley’s project, said research on flies can lead to scientific insights on a wide variety of species.

“From whales to bacteria, many species move collectively,” Puckett said. “Other forms of collective animal behavior can benefit from our study of interactions between individuals.”

Entomology researcher Rebecca Delventhal GRD ’15 said the public does not always place sufficient emphasis on the value of studies in her field.

“I think sometimes the public does not always understand the value of insect research,” Delventhal said in an email to the News. “Insects are incredibly useful as models for biological phenomena that are more difficult to study in more complex organisms.”

Ouellette, Kelley and Puckett plan to continue their research on swarms, hoping to understand what rules guide each individual fly’s behavior in a swarm. Puckett said they have improved the technology used in the research. While they previously used three cameras that would often run out of memory, they now use four and stream the recordings directly to the computer — allowing them to record the swarm continuously from beginning to end.

The research on swarms was funded by the Army Research Office and began in July 2011.

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