Based on their observations, the team figured out that the bugs wander randomly.
If roaches stumble into darkness, they take a break. If a few other cockroaches are nearby under this shelter, they rest longer.
Following these rules, most of the cockroaches eventually assemble under a single shelter, even if another identical shelter is available.
If one shelter casts darker shade than another, the insects gather in the darkest one most of the time.
Initially the researchers had the robots follow these observed rules, so that the bots and the bugs both wound up under the darkest shade in most cases.
For the final round of tests, the team released groups of 12 cockroaches and four robots into an arena with two shades, one darker than the other.
But this time the team programmed the machines to pause beneath the brighter of the two shelters.
Under the influence of the robots, the cockroaches gathered under the brighter shelter more than twice as often as they did when the robots followed regular cockroach rules.
"It's an interesting piece of work," said Ronald Arkin, who studies robot swarms at the Georgia Institute of Technology in Atlanta.
"They have influenced gregarious animals to change their behavior in ways consistent with the [robot] designers' intent."
Halloy and his group will next try to get hatchling chicks to accept a robot as their leader by taking advantage of their inclination to bond with moving objects.
If that works, the researchers will watch to see how the relationship between animal and machine develops.
Halloy noted that has no plans to design robots to interact with humans.
"I must confess that we are not interested in human behavior," he said.
But other experts are, and they say that experiments like Halloy's raise the question of whether robots could be designed to alter the ways humans interact.
Once humans begin interacting with robots more, they may influence us in ways we're not aware of, said Georgia Tech's Arkin, who also co-chairs an international committee that is encouraging discussion about robot ethics.
(Related news: "Robot Code of Ethics to Prevent Android Abuse, Protect Humans" [March 16, 2007].)
"We have to think about those issues especially when dealing with human involvement," Arkin said.
"Cockroaches I'm much less concerned about."
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