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They decide by committee

Sure, the world may end in fire. Or perhaps in ice.

But for those who think the world will end in cockroaches, there may ne new cause for concern. Scientists in Belgium have discovered that the insects are good at collective decision-making

The purpose of the study, by Jean-Marc Ame and Jose Halloy of the Free University of Brussels and colleagues, was not to research the potential ascendancy of cockroaches. Rather, they were trying to understand how gregarious animals, as many apartment dwellers can attest, which cockroaches certainly are, make group decisions.

Cockroaches gather in sheltered locations, or resting places, so the question was how they go about forming groups that maximize protection but minimize overcrowding.

"Resting places are a nice experimental setup to test collective decision-making," Halloy said.

The researchers used larvae of the German cockroach, Battella germanica, placing quantities of them in a Petri dish outfitted with two or more "shelters" - small plastic caps.

No matter the size of the shelters or the number of larvae, the researchers found that the cockroaches would seek a nonrandom, optimal solution. The findings were reported in The Proceedings of the National Academy of Sciences.

For instance, if each of two shelters could fit more then half of the cockroaches, the number in each would be about the same.

But if the shelters were each large enough to handle the whole population, all the larva would gather under one, leaving the other empty.

The behavior is based on very simple interactions among indivigual cockroaches, Halloy said. Through chemical cues, the larvae can detect whether there are other larvae present. And if a shelter gets too crowded, the larvae, who prefer dim locations, can tell that they are out in the light.

"It's a simple way of taking the decision collectively," he said. "It doesn't require any leadership or the exchange of a lot of information."

Such simple decision-making models may apply to other gregarious species like sheep or fish, Halloy said.

"There's nothing intrinsic to cockroaches here," he said. "There's no reason it should be different."

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