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Here are two words to make your blood run cold: robot cockroach. Most people want to destroy cockroaches, but scientists want to understand them. Some researchers specifically wanted to find out more about how these creatures make group decisions. So they sent in the robo-roaches.

NPR's Nell Greenfieldboyce has the story.

NELL GREENFIELDBOYCE: Cockroaches like to be with other cockroaches.

Dr. JOSE HALLOY (Universite Libre de Bruxelles, Belgium): Cockroaches are gregarious insects so they live in groups, and they don't have such sophisticated societies as ants or bees.

GREENFIELDBOYCE: Jose Halloy is a scientist in Belgium who studies group decision-making in animals. He says cockroaches do make simple choices. They like to rest together. Put them in a habitat that has two identical little shelters, shadowed places where they can hang out, and here's what happens.

Dr. HALLOY: They all gather together in the same shadow, below the same shelter. So there is a mechanism that makes the system choose one of the shelters.

GREENFIELDBOYCE: That mechanism isn't one cockroach king decreeing this is our shelter. Instead, the group decision emerges from every individual following some simple rules. Halloy and his colleagues suspected the rules were this. Wander around randomly, but spend more time in a place. If you sense that it is, A, dark, and B, has other cockroaches.

To test this theory, they built a robot cockroach.

Dr. HALLOY: It doesn't look at all like a cockroach. It looks like an electronic matchbox because, in fact, it has to look like a cockroach from a cockroach's perspective.

GREENFIELDBOYCE: Which means it has to smell like a cockroach. When the scientists coded the boxy robot with a chemical - a cockroach smell - the real roaches didn't run away.

Dr. HALLOY: The cockroaches are not at all stressed by the robot because they are perceived as cockroaches. So the cockroach is just accepting that kind of strange buddy. And that's the start of the game.

GREENFIELDBOYCE: The first part of the game was this. Make the robots follow those simple rules, look for dark, look for buddies. The robots had wheels plus a light sensor and an infrared sensor to see nearby roaches. Before long, the robots and the cockroaches were huddled together under the same roof.

Dr. HALLOY: The robots and the cockroaches behave as a group.

GREENFIELDBOYCE: So then Halloy and his colleagues said, okay, let's change one of the rules that the robots follow.

Dr. HALLOY: It's their preference for darkness. We change the preference for darkness. We make the robots prefer lighter places than darker ones.

GREENFIELDBOYCE: And they let the roaches and robots choose between two different shelters: one dark, one filled with light. When they did that, most of the time, they'd find the whole group in the brighter place, even though, normally, roaches would go for the darker one. Basically, the whole group made a bad cockroach decision, because just a few of its members were following a different program.

Halloy and his colleagues have published their experiment in the journal Science. He says don't hold your breath for a robot roach that might lure your kitchen pests into a trap.

Dr. HALLOY: The robot technology is very, very, very low compared to what the insects can do.

GREENFIELDBOYCE: The robots can't climb up walls or wander through pipes. Still, even if it's not good pest control, other researchers say it's good science.

Dr. IAIN COUZIN (Mathematical Biologist, Princeton University): I think it's a really fascinating idea to integrate robots within animal groups. In actual fact, I really feel that this is the future of doing this type of research.

GREENFIELDBOYCE: Iain Couzin is a Princeton University professor who studies group decisions. He says scientists have simulated animal behavior with computer programs. Simple rules can produce virtual schools of fish or flocks of birds. But how do you know these made-up rules are really the ones that the animals use?

Dr. COUZIN: There's a danger in that, you know, you create these rules and you get what appears to be the right phenomena, but there's no real way of testing that.

GREENFIELDBOYCE: He says interactive robots could let scientists do those tests. Couzin wants to go to robots that would swim with the fishes. And Jose Halloy says he'd like to branch out from his work on cockroaches and create a robot chicken.

Nell Greenfieldboyce, NPR News.

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