Evolution and Systematics
Silk of the Darwin's bark spider is twice as strong as other spider silk due to extreme extensibility combined with high strength.
"Combining high strength and elasticity, spider silks are exceptionally tough, i.e., able to absorb massive kinetic energy before breaking. Spider silk is therefore a model polymer for development of high performance biomimetic fibers…We examined the biomechanical properties of silk produced by the remarkable Malagasy 'Darwin's bark spider' (Caerostris darwini), which we predicted would produce exceptional silk based upon its amazing web. The spider constructs its giant orb web (up to 2.8 m2) suspended above streams, rivers, and lakes. It attaches the web to substrates on each riverbank by anchor threads as long as 25 meters. Dragline silk from both Caerostris webs and forcibly pulled silk, exhibits an extraordinary combination of high tensile strength and elasticity previously unknown for spider silk. The toughness of forcibly silked fibers averages 350 MJ m3, with some samples reaching 520 MJ/m3. Thus, C. darwini silk is more than twice tougher than any previously described silk, and over 10 times better than Kevlar®. Caerostris capture spiral silk is similarly exceptionally tough.
Conclusions: Caerostris darwini produces the toughest known biomaterial. We hypothesize that this extraordinary toughness coevolved with the unusual ecology and web architecture of these spiders, decreasing the likelihood of bridgelines breaking and collapsing the web into the river." (Agnarsson et al. 2010:1)
Learn more about this functional adaptation.
- Agnarsson I; Kuntner M; Blackledge TA. 2010. Bioprospecting finds the toughest biological material: extraordinary silk from a giant riverine orb spider. PLoS ONE [Internet],
List of Caerostris species
- Caerostris corticosa Pocock, 1902
- Caerostris cowani Butler, 1882
- Caerostris darwini Kuntner & Agnarsson, 2010
- Caerostris ecclesiigera Butler, 1882
- Caerostris extrusa Butler, 1882
- Caerostris hirsuta (Simon, 1895)
- Caerostris indica Strand, 1915
- Caerostris mayottensis Grasshoff, 1984
- Caerostris mitralis (Vinson, 1863)
- Caerostris sexcuspidata (Fabricius, 1793)
- Caerostris sumatrana Strand, 1915
- Caerostris vicina (Blackwall, 1866)
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