Coordinated Architectural and Chemical Reinforcement in the Crushing Mandible of a Soldier Termite

ABSTRACT

Soldier termites of the dampwood species Neotermes castaneus defend their colonies with crushing‐type mandibles that generate bite forces near the upper end of the range for insects of comparable head width, imposing substantial mechanical demand on a non‐mineralized cuticle. Using a combination of microscopy, spectroscopy, and modeling, we demonstrate how this cuticle accommodates the combined contact and bending loads during defensive biting. Finite element models partition the mandible into two mechanical environments: compressive contact stresses at the convex regions of teeth and bending‐induced tensile stresses in the concave regions between the teeth. These regions coincide with distinct load‐bearing regions and higher hardness at the convex marginal teeth, which contain localized domains of preferentially aligned out‐of‐plane α‐chitin within an otherwise Bouligand‐like lamellar architecture; Atomic Force Microscopy ‐ Infrared Spectroscopy (AFM‐IR) and elemental mapping reveal a through‐thickness sclerotization gradient with relative zinc enrichment confined at the crushing interface, providing contact durability. These findings indicate that a predominantly organic mandible achieves crushing performance through regionally coordinated fiber architecture, sclerotization‐driven stiffness gradients, and surface‐localized chemical hardening and thus offers design principles for lightweight organic composites that rely on regional reinforcement rather than uniform bulk stiffening.