Dragonfly larva's unique ventilation strategy: directed jetting through a controllable tri-leaflet valve

Abstract

Aquatic Anisopteran dragonfly larva possesses a modified hindgut pump that enables jet propelled locomotion and respiration. In supporting these functions, the associated flows are modulated by a tri-leaflet anal valve. Previous studies on this valve have been limited to showing larva's ability to modulate the aperture size through concurrent movement of the three leaflets. However, we have newly observed that the dragonfly nymph's anal valve is capable of more sophisticated movements via independent control of the leaflets. The impact of this unique feature on the two functions of the pump was investigated through simultaneous visualization of the dragonfly's anal valve kinematics and the corresponding anal jets. Our results indicate that by controlling the individual anal valve leaflets, the larva jets its propulsion jet straight by the symmetric nozzle opening, while diagonally deflecting its respiratory jet by the asymmetric nozzle opening. The straight jet during the propulsion appears to reduce the thrust loss due to a side-thrust generation. The deflected respiratory jet appears to induce a secondary entrainment flow in a favorable direction for a clean and efficient breathing.

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