Spider fangs reveal surprises

When we think of spiders, the first thing that comes to mind is their ability to weave intricate and robust webs. But their ability to cut their own silk – the toughest natural material – and strong or tough synthetic fibres such as carbon or Kevlar®, is much less known. A research group coordinated by the University of Trento tried to understand how this is possible. The results of the study have just been published in Advanced Science.

Scientists have long believed that the secret to this effective and precise cutting ability was chemistry or, in other words, the spiders' ability to produce an enzyme capable of dissolving silk fibers. However, this mechanism alone is not sufficient to explain the speed with which spiders perform this operation, for example in a dangerous situation.

"The study – explain Nicola Pugno, Professor of  Solids and Structural Mechanics at UniTrento and corresponding author, and Gabriele Greco, researcher at the Swedish University of Agricultural Sciences and at the University of Trento, corresponding and first author of the study – originates from the curiosity to understand how spiders interact with materials that are not their own. We have created a spider's web using synthetic threads of the same size," i.e. carbon or Kevlar® threads. "But we also wanted to understand how spiders manage to cut their silk, a very strong and extremely tough material, in addition to artificial strands."

Once they have established that chemistry cannot be the only explanation, the team focused on the mechanical action, and observed spiders under a scanning electron microscope. It turned out that the secret to such a precise and effective cut lies in the morphology of the fangs. There is in fact a functionally graded spacing between subsequent serrations, and the spacing increases from the apex of the fang. The fiber to be cut slides inwards until it gets locked in a serrated edge of a comparable size. With this peculiar contact point geometry, the force required to cut the fibers is minimal and the cutting efficiency is maximized.

The results of this study provide valuable information to understand how spiders are able to cut high toughness and strength materials, with interesting prospects for application in other areas. "The new theory – concludes Pugno – could help develop sharper and more performing tools, inspired by spider fangs. For example, for cutting wood, metal, stone, food or hair."

The paper has been published in Advanced Science and can be found at https://doi.org/10.1002/advs.202406079. The data are available in Open Access.

The authors of the study are Gabriele Greco (Swedish University of Agricultural Sciences and University of Trento), Diego Misseroni (University of Trento), Filippo Castellucci (University of Bologna and University of Copenhagen), Nicolò G. Di Novo (University of Trento) and Nicola Pugno (University of Trento).