Bending-activated biotensegrity structure enables female Megarhyssa to cross the barrier of Euler's critical force.

Abstract

The parasitic female Megarhyssa has a hair-like ovipositor capable of withstanding a penetration force 10 times greater than Euler's critical force, using a reciprocating penetration method. Understanding and replicating this penetration mechanism may notably broaden the application scenarios of artificial slender elements. Here, we show that the Megarhyssa's stretched intersegmental membrane and precurved abdomen activate the multipart ovipositor as a biotensegrity structure. The ovipositor's first and second valvulae alternately retract and protract, with each retracted valvula forming a tension network to support the other under compression, resulting in an exponentially increased critical force. We validated this mechanism in a multipart flexible microneedle that withstood a penetration force of 2.5× Euler's critical force and in a lightweight industrial robot that achieved intrinsic safety through its ideal dual-stiffness characteristic. This finding could potentially elucidate the high efficiency of insect probes and inspire more efficient and safer engineering designs.