Computational fluid dynamics provide evidence for a compensatory suction feeding like effect in the predatory strike of dragonfly larvae
Most fast-moving aquatic predators face the challenge of bow wave formation. Water in front of the predator alarms or even displaces the prey. To mitigate the formation of such a bow wave, a strategy aiming at pressure reduction via suction has evolved convergently in several animal groups: compensatory suction feeding. The aquatic larvae of dragonflies and damselflies (Insecta: Odonata) are likely to face this challenge as well. They capture prey underwater using a fast-moving raptorial appendage, the so-called prehensile labial mask. Within dragonflies (Odonata: Anisoptera) two basic shapes of the prehensile labial mask have evolved, with an either flat and slender or concave distal segment. While the former is a pure grasping device, the latter is also capable of scooping up smaller prey and retaining it inside the cavity by arrays of bristle-like structures. The hydrodynamics of the prehensile labial mask was previously unknown. We used computational fluid dynamic (CFD) simulations of the distal segment of the mask, to investigate for the first time how different shapes of the mask impact their function. Our results suggest that both shapes are highly streamlined and generate a low-pressure area, likely leading to an effect analogous to compensatory suction feeding. This presents a vivid example of how convergent evolution enables very different animal groups to successfully deal with the challenges of their environment. It may also be an interesting concept for technical application in small scale grasping devices; e.g. for simple sampling mechanisms in small-sized autonomous underwater vehicles (AUVs).