A novel passive selective cutting mechanism inspired by the ovipositors of sawflies

The female sawfly (Insecta: Hymenoptera, Symphyta) uses a double blade reciprocating saw-like ovipositor to cut into plant tissue and lay its eggs within the cut. Whereas extensive study was carried out for wood-boring ovipositors, little is known about how sawflies achieve such controlled cutting in soft substrates. This suggests a mechanism that balances effective cutting with minimal tissue disruption. This article reports a novel passive selective cutting mechanism in which the saw discriminates between material properties of the plant tissue without active sensing or external control, something rarely achieved in human-made systems. Scaled-up biomimetic blades replicating key ovipositor features were tested on synthetic substrates (agar and ballistic gelatine) across a range of stiffnesses. Experimental results reveal a force-dependent threshold above which the saw is displaced rather than cutting. This threshold depends on the interaction between the shape of the saw teeth and the substrate properties and is consistent across multiple sawfly species. These findings reveal a previously undescribed bioinspired cutting principle with potential for surgical tools that avoid damaging sensitive tissues, and broader applications where passive, material-specific selectivity is required without the complexity of sensors or active feedback control.