How effective are insect aposematism and Batesian mimicry in deterring a wild avian predator?

Batesian mimicry manifests in amazing forms, yet empirical studies quantifying its efficiency in nature are virtually absent. Lepidopterans include striking mimics of aposematic hymenopterans. Imitations may include not only visual components, but also acoustic and chemical signaling. We evaluated whether hymenopteran-mimicking clearwing moths (Lepidoptera: Sesiidae) and diurnal hawkmoths (Lepidoptera: Sphingidae) complement visual anti-predator signaling with acoustical mimicry. Through field-based experiments, we then compared the response of an avian predator, the European robin (Erithacus rubecula), to hymenopteran models and their lepidopteran mimics. Our work contradicts the assumption that aposematism and Batesian mimicry provide generalized protection to insects, paving the way for comparative studies involving a broader range of predators. We verified two predictions: (1) robins discriminate among different models based on their perceived risk, with avoidance behavior occurring in response to more harmful stimuli; (2) predators respond similarly within each studied pair of model and mimic. We demonstrated a clear distinction in the reaction of robins to the hornet Vespa crabro and its mimic, the hornet clearwing Sesia apiformis, in comparison to all other tested species, strongly indicating that the presence of the hornet and hornet mimic deterred the birds.