Dragonfly larvae capture their prey with a strongly modified -extensible-mouthpart using 9 a biomechanically unique but not yet understood mechanism. The current opinion of hydraulic 10 pressure being the driving force of the predatory strike can be refuted by our manipulation 11 experiments and reinterpretation of former studies. On this fact, we present evidence for a 12 synchronized dual-catapult system powered by two spring-loaded catapults. The power output of the 13 system exceeds generally the maximum power achievable by musculature. Energy for the movement 14 is stored by straining a resilin-containing structure at each joint and possibly the surrounding cuticle 15 which is preloaded by muscle contraction. To achieve the precise timing required to catch fast-moving 16 prey, accessory structures are used to lock and actively trigger the system, ensuring the 17 synchronisation of both catapults. As a proof of concept, we developed a bio-inspired robotic arm 18 resembling the morphology and functional principle of the extensible mouthpart. Our study elucidates 19 the predatory strike of dragonfly larvae by proposing a novel mechanism, where two synchronized 20 catapults power the ballistic movement of prey capturing in dragonfly larvaea so-called 21 synchronized dual-catapult system. Understanding this complex biomechanical system may further 22 our understanding in related fields of bio inspired robotics and biomimetics. 24One Sentence Summary: The synchronized dual-catapult, a biomechanically novel 25 mechanism for the ballistic movement of prey capturing in dragonfly larvae 26 27 Keywords: biomechanics; functional morphology; catapult system; ballistic movement; 28 power modulation; robotic arm 29 42 Cicadomorpha; 4, 6). Here a catapult-like elastic mechanism is used to perform one of the fastest 43 jumps known by using chitinised cuticle as a spring (3). The elastic protein resilin rapidly returns the 44 leg to its original shape after a jump (using the jumps energy) and allows for repeated jumping (6). 45Resilin represents an essential element of high resilience, low fatigue, and damping mechanisms in 46 arthropods (12) due to its viscoelastic properties (13). In the specific case of a catapult system, the 47 near-perfect resilience (92-97%) and a fatigue limit of over 300 million cycles (14) in combination 48 with the ability to stretch to over three times its original length and recoil to its initial state without 49 plastic deformation (15,16) become important. 51Our example here, is the predatory strike Odonata (dragonflies and damselflies) larvae use to capture 52 preythey evolved a strongly modified, extensible mouthpart called prehensile labial mask ( Fig. 1A; 53 17,18). These larvae are key predators in their freshwater habitats, hunting invertebrates as well as 54 small vertebrates like tadpoles or fish from an ambush (19). These insects can project their specialised 55 mouthpart towards the prey, enabling the larvae to hunt effectively (see supplementary movie S1; 18). 56Previous investigati...

Most fast-moving aquatic predators face the challenge of bow wave formation. Water in front of 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 the compensatory suction feeding. This might be an interesting concept for technical application in small scale grasping devices, e.g. for simple sampling mechanisms in small-sized autonomous underwater vehicles (μAUVs).

The larvae of Odonata are limnic predators capable of catching their prey using a highly modified mouthpart – the labium. Driven by a unique dual catapult mechanism, the apparatus can reach peak accelerations of up to 114.5m/s2. Yet little is known about the kinematics of the predatory strike in an ecological context. Here we show how different ambient temperatures affect the predatory strike and the avoidance reaction of prey items of Odonata larvae. We found that the extension velocity of the labial mask decreases significantly with the ambient temperature both in dragonflies and damselflies. However, temperature has lesser impact on the predatory strike itself than on directly muscle driven movements in both the predator and prey items. This contradicts the previous assumption that catapult mechanisms in insects are unaffected by temperature. Our results indicate that the prehensile labial mask is driven by a series-elastic catapult; a mechanism similar to the temperature dependent jump of frogs, where muscle and spring action are tightly linked. Our study provides novel insights into the predatory strike of Odonata larvae and offers a new ecological perspective on catapult mechanisms in arthropods in general.