These hydraulic mechanisms are generated by the use of several muscles on both sides of the abdominal diaphragm, thereby generating pressure waves as required. Both the mechanisms are hypothesized to function based on similar hydraulic dynamics. Firstly, the self-propulsion that is achieved by generating jets from the anal valve, and secondly, the labium protraction for capturing the prey.

The process of capturing the prey involves two primary mechanisms. After the prey is captured, it is drawn towards the mouth to be fed on. Once the palpi reach around the prey, they are brought together to form a closed cup shape to grab the prey. Depending on the distance of the prey from the mouthpart, the forward movement was observed to be assisted by the movement of the body. This involves a gradual opening up of the two cup-shaped labial palpi and moving them forward with the help of unfolding prementum and postmentum parts, similar to the extension of human arms with the elbow and shoulder joints. The predatory strike in dragonfly nymphs is performed by using the labium that is modified into a prehensile mask for capturing the fast-moving prey. Earlier studies suggest that prey detection may also be achieved by sensing the underwater currents with the use of mechanoreceptors on the legs of the nymphs of L.depressa. Prey-capturing by a dragonfly nymph involves visually locking onto the prey to be captured and, in certain cases, pressure build-up in the abdomen with water that helps generate quick forward movement using propulsion. They are also the only insects or animals that are known to have a modified underlip that is used as a protractile organ, referred to as a labium. They are proven to be a potential bio-control agent of mosquitoes. Dragonfly nymphs are another example, which are voracious predators that feed on tadpoles, mosquito larvae and other smaller aquatic organisms. An example of such a kind of movements is the predatory strike of a mantis shrimp. Such rapid movements in many animals are expected to be an outcome of evolutionary pressures such as escaping from predators and catching fast prey. Some of these predatory insects use rapid movements to catch the prey. In this group of insects, there is a huge diversity in the broad classification of predators and prey, and some of the top predators have been identified as diving beetles, bugs and dragonfly larvae Aquatic predation presents a complex scenario of mechanics, primarily because of the hydrodynamic drag forces experienced during the motion of the predator and its prey-capturing mechanism. Thus, studying such mechanisms with their sensory capabilities provides a unique opportunity to design and develop bioinspired underwater deployable mechanisms.Īquatic insects are one of the most diverse groups of animals in small water bodies. Such mechanical properties of the mandibles make them hard tools that can cut into the exoskeleton of the prey and also resistant to wear. The Young’s modulus and hardness of the mandibles were estimated to be 9.1 ± 1.9 GPa and 0.85 ± 0.13 GPa, respectively. The time taken for the protraction and retraction of labium during prey capture was estimated to be 187 ± 54 ms, suggesting that these nymphs have a rapid prey mechanism.

The morphological details suggest that the prey-capturing labium is a complex grasping mechanism with additional sensory organs that serve some functionality. To observe and analyze the preying mechanism under water, we used high-speed photography and, electron microscopy. Thus, we examine two main mouthparts of the dragonfly nymph (Libellulidae: Insecta: Odonata) that are used in prey capturing and cutting the prey. Dragonfly nymphs are known to be voracious predators with structures and movements that are yet to be fully understood. Aquatic predatory insects, like the nymphs of a dragonfly, use rapid movements to catch their prey and it presents challenges in terms of movements due to drag forces.

Dragonfly larvae predators