The scientists observed that two key, indirect interactions governed the nest-building activity.
First, chemistry played a role. Ants tended to lay building materials atop other material left in the same place, as opposed to putting them in another, new spot. What told them to build upon previous work? It turns out, the scientists learned, the ants were adding a pheromone to the building material, leaving behind a chemical signal other ants used to build atop the same spot and, thus, build the individual pillars.
Second, the ants took their cues for the physical size of the pillars by using their own body dimensions. Whenever a pillar grew as high as a typical ant's body length, the little builders knew it was time put a cap on that pillar and begin building laterally the next section.
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The researchers say the lifetime of the pheromone - how quickly it breaks down and loses its "power" over the ants - was dependent upon climate and that different climates resulted in different nest structures.
In drier environments, the pheromone broke down faster, which resulted in fewer pillars being built and, therefore, roomier chambers that could fit more ants, the better to conserve humidity.
But in more humid environments, the team found, the pheromone lasted longer, resulting in more pillars and smaller chambers.
The researchers -- comprised of scientists from CNRS, Université Toulouse III – Paul Sabatier and Université de Nantes -- published its findings in the January 18 issue of PNAS.