From passive defense to multimodal deterrence: novel antipredator behavior in the javelin sand boa Eryx jaculus Linnaeus, 1758 (Squamata: Boidae)

Dorsolateral flattening is a defensive behavior observed in several snake taxa, typically involving lateral expansion of the body to increase apparent size and deter predators. Although this behavior has been documented in other snake families, its occurrence in boid snakes remains poorly understood. Here, we present the first confirmed field observations of full-body dorsolateral flattening in Eryx jaculus, a boid species native to southeastern Europe. The behavior was recorded under natural conditions during close approach, attempted capture, or brief handling and involved coordinated lateral expansion along the entire body trunk. In several cases, flattening was accompanied by mock strikes, mainly expressed during attempted capture. These observations indicate a multi-modal defensive strategy that combines visual and behavioral deterrents. This expands the known behavioral repertoire of Boidae and supports the hypothesis that full-body flattening may represent a convergent trait evolved independently across phylogenetically distant lineages. We discuss the anatomical basis, ecological context, and potential adaptive significance of these behaviors, contributing new insights into snake defensive strategies within European species assemblages. More broadly, this study provides new insight into the defensive ecology of a poorly documented European boid and highlights the importance of opportunistic field observations for detecting rare or context-dependent antipredator behaviors.