Avian predators avoid attacking fly-mimicking beetles: A field experiment on evasive mimicry using artificial prey

AbstractMany Neotropical beetles present coloration patterns mimicking red-eyed flies, which are presumably evasive mimicry models. However, the role of predators in selecting for evasive mimics in nature remains untested. In a field experiment, we used nontoxic plasticine replicas of a specialized fly-mimicking beetle species, which we placed on the host plants of the beetles. We show that replicas painted with reddish patches simulating the eyes of flesh flies experienced a much lower predation rate than control replicas. We found that beak marks were the most frequent signs of attack on plasticine replicas, underlining the potential selective pressure exerted by birds. Replicas that matched the size of the beetles suffered higher predation than smaller or larger replicas. The predation rate was also higher for beetle replicas exposed during the warm and wet season, when adult beetles occur. Our results support predator-mediated selection of mimic beetles, highlighting that reddish spots resembling flies' eyes comprise an important trait in reducing attack by avian predators.