The prey-capture glues produced by orb-weaving spiders and their evolutionary descendents, cobweb-weaving spiders, respond differently to humidity because of different ‘tackifiers’ used in the two types of glue. These findings, published in Scientific Reports, could help future efforts to make smart materials that are resistant or sensitive to certain stimuli.
Orb-weaving spiders and cobweb-weaving spiders capture prey using adhesive silk threads coated in glue but although the two types of glue are produced in homologous glands, they differ greatly. Viscid glue, produced by orb-weaving spiders, is adapted for capturing flying insects and is humidity-sensitive, its adhesion maximized at intermediate humidity. The gumfoot glue produced by cobweb-weaving spiders is adapted for catching walking insects and is mainly resistant to humidity, maintaining its stickiness at extreme humidity levels.
Ali Dhinojwala and colleagues examined individual droplets of glue produced by the two spider lineages. Despite their close evolutionary homology, the two bio-adhesives proved to be remarkably different, particularly with respect to their interactions with water. Cobweb weavers use a cocktail of short peptides and long adhesive polymers (probably glycoproteins), which means the glue is resistant to variations in humidity. Viscid glue, on the other hand, is highly responsive to water thanks to the hygroscopic salts it contains, and the glue is stickiest at intermediate humidity.
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