Scanning electron micrograph (SEM) of Northern black widow spider (Latrodectus variolus) egg case, multi-stranded silk. Cribellar glands produce multi-stranded, slightly sticky silk through many pores which are combed with special hairs on the hind legs of black widow spiders. It emerges to form fluffy woolly silk. Multi strands of spider silk are laid in the web or egg cases to withstand adverse conditions and impact created by fast moving prey. Black widow spider silk is as strong as orb weaver spider silk (tensile strength approx.1000 MPa). The tensile strength of spider silk is comparable to that of steel wire of the same thickness. Since the density of steel is about six times that of silk, spider silk is stronger than steel wire of the same weight. Magnification: x295 when shortest axis printed at 25 millimetres.
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