THE COMBS OF HONEYBEES AS COMPOSITE MATERIALS

Abstract

Mechanical changes in the combs of the African honeybee, A. m. scutellata, in relation to maturation and temperature were measured. Combs ranged in colour from white to brown and varied in silk content from 0 to 34 % . New brood comb proceeds from a single-phase material, pure wax, to a fibre-reinforced composite. Fibroin, a crystalline and hygroscopic protein, is spun randomly on the cell walls making them planar isotropic. This silk fraction is mechanically constant between 25 °C and 45 °C. Comb wax is an isotropic plastic having no unique mechanical constants. The stiffness, strength and fracture energy of comb wax decreased with increasing temperature. When silk is present in comb cell walls, making them a two-phase material, comb strength and stiffness are greatly enhanced. Fibroin thus greatly contributes to the mechanical integrity of combs. Mature brood combs are a compromise between the very different materials, wax and silk, which when combined produce a structure with new properties that differ from its individual constituents.