Ants acknowledge information to control its rate of transfer

Signals whose function is solely to coordinate communication are so far known only in human conversations1 and telecommunication networks2. Utterances like "mm-hmm"3, gestures such as the nodding of ones head, or "ACK" packets used in Internet protocols to confirm the reception of a message4 all coordinate communication. Rather than carrying domain-specific information5-7, these signals are generic acknowledgements used by receivers to control the flow of sender information when the rate of information transfer could possibly be overwhelming. Here, we show the first evidence of the use of acknowledgements to control information transfer rates outside human society. Quantitative comparison of information flows between sender-receiver pairs demonstrates that acknowledgements are used by pairs of ants during tandem running8,9--a social behaviour where the sender facilitates the receivers intake of navigational information--but not by pairs of termites that also tandem run10,11 to maintain cohesion but not to share large amounts of information. Our analysis provides a quantitative framework for identifying in other animal taxa hidden patterns of information flow with implications for uncovering cryptic signals within complex communication behaviours that are still poorly understood12,13.