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Individually Marked Ants
Stephen Pratt
Department of Ecology and Evolutionary Biology
Ant colonies show remarkably coordinated behavior, despite lacking any direction from a well-informed central controller. Each worker instead applies simple decision rules to limited knowledge, and exchanges information with her neighbors using rudimentary cues and signals. From this process emerge the construction of complex nests, collective decisions among food sources, the adaptive allocation of labor across tasks, and many other group accomplishments. To identify the underlying decision rules requires a detailed description of the behavior of individually identifiable ants. The ant species Temnothorax curvispinosus is especially useful for this kind of study, because they form small colonies of only a few hundred workers, and they thrive in thin, glass-walled laboratory nests, facilitating detailed video records of their behavior. Most importantly, as shown in these images, workers can be individually marked with tiny drops of paint. Ants are first immobilized with carbon dioxide, and then marked with a distinctive pattern of four drops. They soon emerge unharmed from narcosis, and retain their marks for several months to years. This approach has been particularly useful in showing how emigrating colonies can choose the best among several new homes, even when few individual workers are aware of all the options under consideration.