Call it the ant version of Facebook. A new study finds that, whereas most red harvester ants share information with a small number of nestmates, a few convey news to a wide network of others. The results help explain how ant colonies quickly respond to predators and natural disasters. Red harvester ants (Pogonomyrmex barbatus) are native to the deserts in the American Southwest and live in large colonies of several thousand individuals. Most social interactions occur in the colony's entrance chamber. At first light, patroller ants emerge from the colony to ensure that the surrounding area is free from predators and natural hazards. If most of the patroller ants return, they signal forager ants that it's safe to gather seeds, their primary food.
Like all ants, red harvester ants use chemical signals to send information. The ants secrete small molecules on their exoskeletons, and their nestmates rub the exoskeletons with their antennae—the ant equivalent of “Hi, how are you?”—to read these signals. The particular combination of chemicals on an ant's exoskeleton can provide information on what task an ant performs (patroller versus forager), where it has been, and what food it has found. Researchers at Stanford University in Palo Alto, California, measured information exchange in red harvester ants by counting the number of antennae meet and greets each ant experienced in a mock entrance chamber in the lab. The scientists videotaped the entire scene and then used a sophisticated computer program to identify each ant and count how many interactions it had during the experiment (see video). The researchers measured 4628 interactions during a trial with red harvester ants from each of two different colonies.