Adhesive latching and legless leaping in small, worm-like insect larvae

Abstract

ABSTRACT Jumping is often achieved using propulsive legs, yet legless leaping has evolved multiple times. We examined the kinematics, energetics and morphology of long-distance jumps produced by the legless larvae of gall midges (Asphondylia sp.). They store elastic energy by forming their body into a loop and pressurizing part of their body to form a transient ‘leg’. They prevent movement during elastic loading by placing two regions covered with microstructures against each other, which likely serve as a newly described adhesive latch. Once the latch releases, the transient ‘leg’ launches the body into the air. Their average takeoff speeds (mean: 0.85 m s−1; range: 0.39–1.27 m s−1) and horizontal travel distances (up to 36 times body length or 121 mm) rival those of legged insect jumpers and their mass-specific power density (mean: 910 W kg−1; range: 150–2420 W kg−1) indicates the use of elastic energy storage to launch the jump. Based on the forces reported for other microscale adhesive structures, the adhesive latching surfaces are sufficient to oppose the loading forces prior to jumping. Energetic comparisons of insect larval crawling versus jumping indicate that these jumps are orders of magnitude more efficient than would be possible if the animals had crawled an equivalent distance. These discoveries integrate three vibrant areas in engineering and biology – soft robotics, small, high-acceleration systems, and adhesive systems – and point toward a rich, and as-yet untapped area of biological diversity of worm-like, small, legless jumpers.