Abstract: The cuticle of a maggot goes through a mechanical transition when it dries, increasing in stiffness by about an order of magnitude (e.g. from 0.5 GPa to 5 GPa) as the water content drops from about 1 g/g (weight of water perunit dry weight ) to 0.4 g/g. Thus stiffness represents the loss of freezable water and is more or less diagnostic of a material stabilized by hydrogen bonds. Further loss in water results in a smaller increase in stiffness. In natural systems the water content is controlled by the addition of phenolic residues, resulting in tanning or sclerotisation, which drives the matrix components towards cooperative in teraction and makes the material permanently waterproof.

Key words: water content, hydrogen bonding, mechanical transition, beta proteins, tanning, cuticle