Exploring dynamics of nature's raincoat: comparing how nano-scale silk fibers produced by dryland and tropical species of webspinning insects interact with water.

Abstract

Embiopterans are reliant on silk for protection and produce the finest silk fibers known in nature. This report compares silk-water interactions for four species representing two different lifestyles: two tropical arboreal species that feed on lichens on bark and two detritivores from arid regions that typically live in leaf litter and underground. Water droplets placed on spun silk transformed the fibrous top layer to a film. Arboreal embiopterans spun a denser silk covering than did the detritivores. The films that formed after exposure to water were also denser for the arboreal species. A possible underlying cause for the difference between the two lifestyles is because detritivores stitch together dried leaves and other detritus to create cover, they may rely more on substrate than on silk alone for protection. In contrast, arboreal embiopterans exposed on the surface of bark rely on thick silk coverings. Contact angles of water droplets on silk revealed that the silks tended to be more hydrophilic than a hydrophobic control, perhaps explaining why silks exposed to water become transformed by water-protein interactions. Results suggest that interesting variability in silk-water interactions exists for this little-known group insects, that also produce silk proteins of high crystallinity and with variable amino acids, one species to the next.