It is amazing how complex social organisations simply self assemble, but this is exactly what ant nests do. Sticking to their simple functions, neighbouring foragers, nurses and maintenance workers interact and contribute to build the community's sophisticated structure. By ant standards, Temnothorax albipennis live in relatively small fragile colonies and each time a colony is destroyed, the residents use their powers of self-organization to select a new nest site from possible alternatives before emigrating. However, it occurred to Nathalie Stroeymeyt and Nigel Franks from the University of Bristol, UK, and Martin Giurfa from the University of Toulouse, France, that most studies investigating ant emigration have focused on naïve insects that had been transported to an unfamiliar location. However, in reality, ants usually relocate to a nearby crevice with which they may already be familiar. The team wondered whether knowledgeable scouts and foragers that had stumbled across attractive alternative locations when the nest was secure could use this information to direct the nest's collective decision and guide the emigrating colony quickly to a new home after a disaster (p. 3046).

Stroeymeyt collected T. albipennis nests from their coastal homes in the southern UK and relocated them to the lab. Providing each community with a comfortable artificial nest in a wellsupplied and spacious arena, Stroeymeyt placed an alternative nest site some distance from the ants' home and recorded the insects' movements as they familiarised themselves with the surroundings. Then, a week later, Stroeymeyt carefully destroyed their home – after placing a second unfamiliar nest site on the opposite side of the arena – and recorded the entire emigration as the ants worked frantically to relocate. But which nest site would the ants occupy? Would they follow scouts that had learned about the attractive alternative site during earlier exploration, or would they search randomly, relying only on their powers of self-organisation in the hope of stumbling across a desirable location?

After months of painstaking analysis by Stroeymeyt, the team realised that the ants eventually followed the informed scouts to the familiar alternative nest that had been in the enclosure all along. Initially some of the insects went scampering off in all directions, but a few of the ants – which had discovered the location of the alternative site while scouting – ran straight to it. Having decided that the familiar site would make a good new home, they returned quickly to the devastated nest to recruit more colleagues, repeating the process and enlisting more followers until enough of the community had assembled at the new site and the decision made to relocate the entire population.

Stroeymeyt also tested whether the informed ants relied on pheromone trails to direct them swiftly to their new home or navigated using visual memories of their surroundings and found that the ants were guided by their visual memories. According to Stroeymeyt, any member of the colony in most ant species can usually follow pheromone trails, while memories are only accessible to their owner. This led her to conclude that instead of following publicly available trails, relocating nestmates are being actively led by guides with access to privileged knowledge about the new nest site.

So, even though complex ant nest societies naturally self assemble thanks to the inhabitants' simple behaviour patterns, it appears that some well-informed ants shape the collective decision-making process by leading from the front.

N. R.
Knowledgeable individuals lead collective decisions in ants
J. Exp. Biol.