Bimodal distress signals of Western carpenter ants upturn alarm responses of nestmates

When threatened, many social insects produce alarm signals that alert and recruit nestmates. Ants commonly communicate distress using both pheromonal and vibratory signals. We have previously shown that distressedWestern carpenter ants, Camponotus modoc, emitalarm pheromone that attracts nestmates and that their drumming on substrate generates vibrations that prompt their nestmates to freeze. Here, we tested the hypothesis that pheromonal and vibratory signals in combination elicit the strongest and fastest alarm response from nestmates. To test this hypothesis, we video-recorded the behavior of groups of ants on wood veneer in response to (i) synthetic alarm pheromone, (ii) laser-guided play-back recordings of vibratory signals, or (iii) pheromonal and vibratory signals in combination. The bimodal signals did not enhance attraction of nestmates but they significantly upturned the freezing response of nestmates. Immediate and prolonged freezing is likely adaptive in the context of predator avoidance because ant movement provides a strong visual cue for predators such as insectivorous woodpeckers.