The majority of spiders spin silk threads several micrometers thick, but the orb spider Uloborus plumipes can spin nano-scale filaments.
The feather-legged lace weaver (Uloborus plumipes). Image credit: Olaf Leillinger / CC BY-SA 2.5.
Instead of using sticky blobs of glue on their threads to capture prey, Uloborus plumipes (also known as the feather-legged lace weaver) spiders use a more ancient technique – dry capture threads made of thousands of nano-scale filaments that it is thought to electrically charge to create these fluffed-up catching ropes.
To discover the secrets of Uloborus plumipes’ nano-fibers, Oxford University scientists Dr Katrin Kronenberger and Prof Fritz Vollrath collected adult female from garden centers in Hampshire, UK. They then took photographs and videos of the spiders’ spinning action and used three different microscopy techniques to examine the spiders’ silk-generating organs.
Of particular interest was the cribellum, an ancient spinning organ not found in many spiders and consisting of one or two plates densely covered in tiny silk outlet nozzles.
“Uloborus plumipes has unique cribellar glands, amongst the smallest silk glands of any spider, and it’s these that yield the ultra-fine catching wool of its prey capture thread,” said Dr Kronenberger, the first author of a paper published in the journal Biology Letters.
“The raw material, silk dope, is funneled through exceptionally narrow and long ducts into tiny spinning nozzles or spigots. Importantly, the silk seems to form only just before it emerges at the uniquely-shaped spigots of this spider.”
The cribellum of Uloborus plumipes is covered with thousands of tiny silk-producing units combining ducts that average 500 nm in length and spigots that narrow to a diameter of around 50 nm.
“The swathe of gossamer, made of thousands of filaments, emerging from these spigots is actively combed out by the spider onto the capture thread’s core fibers using specialist hairs on its hind legs,” Prof Vollrath said.
“This combing and hackling – violently pulling the thread – charges the fibers and the electrostatic interaction of this combination spinning process leads to regularly spaced, wool-like puffs covering the capture threads.”
“The extreme thinness of each filament, in addition to the charges applied during spinning, provides Van der Waals adhesion. And this makes these puffs immensely sticky.”
Conventionally, synthetic polymers fibers are produced by hot-melt extrusion: these typically have diameters of 10 micrometers or above.
But because thread diameter is integral to filament strength, technology that could enable the commercial production of nano-scale filaments would make it possible to manufacture stronger and longer fibers.
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Katrin Kronenberger & Fritz Vollrath. Spiders spinning electrically charged nano-fibres. Biology Letters, published online January 28, 2015; doi: 10.1098/rsbl.2014.0813
