Multifunctional Adhesives on the Eggs of the Leaf Insect Phyllium philippinicum (Phasmatodea: Phylliidae): Solvent Influence and Biomimetic Implications

Leaf insects (Phylliidae) are well-camouflaged terrestrial herbivores. They imitate leaves of plants almost perfectly and even their eggs resemble seeds—visually and regarding to dispersal mechanisms. The eggs of the leaf insect Phyllium philippinicum utilize an adhesive system with a combination of glue, which can be reversibly activated through water contact and a water-responding framework of reinforcing fibers that facilitates their adjustment to substrate asperities and real contact area enhancement. So far, the chemical composition of this glue remains unknown. To evaluate functional aspects of the glue–solvent interaction, we tested the effects of a broad array of chemical solvents on the glue activation and measured corresponding adhesive forces. Based on these experiments, our results let us assume a proteinaceous nature of the glue with different functional chemical subunits, which enable bonding of the glue to both the surface of the egg and the unpredictable substrate. Some chemicals inhibited adhesion, but the deactivation was always reversible by water-contact and in some cases yielded even higher adhesive forces. The combination of glue and fibers also enables retaining the adhesive on the egg, even if detached from the egg’s surface. The gained insights into this versatile bioadhesive system could hereafter inspire further biomimetic adhesives.