

Some worker ants are more equal than others.

As with other social insects, it was once thought that workers were essentially equivalent in ant colony hierarchies. But it appears that a few well-informed individuals shape group decisions by leading nestmates to new homes.

The findings could add a new dimension to ant-derived models of self-organization.

"Although self-organized systems appear very effective under the assumption that all individuals follow the same simple set of rules, the presence of key, well-informed individuals altering their behavior according to their prior experience might generally enhance performance even further," wrote biologists from the University of Bristol and the University of Toulouse in an Aug. 24 Journal of Experimental Biology paper.

To study nest-hunting, Nathalie Stroeymeyt and colleagues Nigel Franks and Martin Giurfa collected "house-hunting" ants, or Temnothorax albipennis, from the southern coast of the United Kingdom. These small, light-brown ants make simple sand-enclosed nests in the cracks of rocks.

Moving the ants into the lab, Stroeymeyt gave them a well-supplied artificial nest. She then placed an identical empty nest site at the opposite end of the ants' territory. Each ant's back was painted with individually-identifiable colored spots. Webcams and motion-detection software allowed the researchers to keep track of the movements of specific ants.

One week later Stroeymeyt placed a second unfamiliar nest site in the territory and destroyed their original home. Though some ants began to run around randomly in all directions, a few ants who had already explored the alternate nest site headed directly to it.

Those ants then quickly returned to the destroyed nest to recruit followers. They repeated the process until enough had gathered at the new nest site to relocate the entire colony.

Most studies of how ants find new nest sites use colonies unfamiliar with a new territory, and assume that all workers follow the same rules. But that's not realistic, and as a model for self-organization and distributed decision-making – ants have inspired various forms of traffic coordination, from cars to data – it might not be optimally efficient.

"This begins to change how we think about self-organization," said Nicola Plowes, a behavioral ecologist and ant specialist at Arizona State University, who was not involved in the research. "Informed individuals making those decisions actually result in a process that is more efficient than a simple homogeneous self-organized system."

The findings will be exciting for technologists and mathematicians who use insect-based algorithms, Plowes believes.

"Sky Harbor International Airport, for example, uses ant-based algorithms for its baggage carriers," she said. "Knowing that we can incorporate informed individuals, you can actually make it work better and faster."

Image: 1) s.alt/Flickr. 2) April Nobile, copyright 2007/AntWeb.org.* *

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Citation: "Knowledgeable individuals lead collective decisions in ants." By Nathalie Stroeymeyt, Nigel R. Franks and Martin Giurfa. Journal of Experimental Biology. August 24, 2011.