This spider’s silk is over 10 times tougher than Kevlar

In the rainforests of Madagascar, Darwin’s bark spider (Caerostris darwini) does something almost no other spider on Earth can do: it spins a single silk bridge across an open river, then builds a giant web on top of it. What makes the feat possible is not just patience but the silk itself, which scientists have identified as the toughest biological material ever studied, combining exceptional strength with remarkable elasticity.

The spider was discovered in Madagascar in 2009, and unlike most orb-weavers that build between nearby branches, it stretches a single bridge line across open water before constructing the rest of the web. According to Keio University, that anchor thread can span up to 25 metres, while the sticky orb itself can cover as much as 2.8 square metres, making it the largest known web built by a single spider. Researchers are still uncertain exactly how the spider manages to establish that first bridge across such a vast gap; the leading hypothesis is that it releases silk into the wind until the thread catches vegetation on the far bank, then reinforces the line before weaving the rest of the web.

Research led by Dr Ingi Agnarsson of the University of Puerto Rico and Dr Matjaž Kuntner of the Scientific Research Centre of the Slovenian Academy of Sciences and Arts found that the spider’s dragline silk has an average toughness of around 350 megajoules per cubic metre, with some samples reaching 520 MJ/m³. That makes it more than twice as tough as previously studied spider silks and over 10 times tougher than Kevlar of comparable size, the synthetic fibre widely used in body armour.

A 2021 review published on PubMed explains why this matters: spider silk is remarkable because it combines high tensile strength with exceptional extensibility, giving it outstanding toughness and the ability to absorb energy before breaking. Unlike most synthetic materials, which tend to be either strong or flexible but rarely both, spider silk achieves both properties at once.

A study led by Markus J. Buehler at the Massachusetts Institute of Technology, alongside Steven Cranford, Anna Tarakanova and Nicola Pugno, found that the silk behaves in a highly sophisticated, nonlinear way under stress. Under light loads such as wind, the web stays stable and holds its shape; under stronger local impacts, such as a large insect striking it or falling debris, the silk temporarily softens before stiffening again, confining the damage to a small area rather than letting the whole web collapse.

More than a decade after its discovery, Darwin’s bark spider continues to interest engineers and materials scientists, who hope that understanding how it produces such resilient silk could eventually inspire lighter protective equipment, stronger medical sutures and advanced textiles.

Wikimedia Commons/by Agnarsson, Kuntner & Blackledge