A common British spider, frequently found in garden centers is offering researchers insight into how to strengthen synthetic fibers.
The silk that most spiders produce for their webs is several micrometers thick and sticky. Uloborus plumipes, commonly known as the ‘garden centre spider’ or ‘feather-legged lace weaver’ spins filaments just a few nanometers thick.
Recently a team from Oxford University took a close look at the spider to try to understand how this unusual silk is produced.
Instead of using glue on their threads to capture prey, Uloborus plumps uses dry capture threads made of thousands of nano-scale fibres. The researchers believe that the thin filaments are able to generate an electric charge.
To discover how this is accomplished the researchers collected adult, female Uloborus spiders from Hampshire, UK garden centers. They took photos and videos of the spiders while they created webs and examined the arachnids silk generating organs using three different microscopy techniques.
The researchers were particularly interested in the cribellum which consists of one or two plates densely covered in small silk nozzles. This method of generating silk is thought to predate the more common spinnerets found in most spiders. As of 1991 only 180 types of spiders are known to have cribellum.
“Uloborus 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. The raw material, silk dope, is funnelled 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,” said Dr Katrin Kronenberger of Oxford University’s Department of Zoology.
Kronenberger is, along with Fritz Vollrath, the author of a paper which appears journal Biology Letters.
According to the researchers, the cribellum of Uloborus has thousands of silk producing units. These units include ducts averaging 500 nanometers in length and spigots of about 50 nanometers.
‘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 fibres using specialist hairs on its hind legs. This combing and hackling – violently pulling the thread – charges the fibres 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,’ said Vollrath, also of Oxford’s Department of Zoology.
Synthetic fibers are generally produced by “hot-melt extrusion”. These fibers have a diameter of 10 micrometers or more. Thread diameter has a significant impact on the strength of materials. If researchers can mimic the silk production methods of the Uloborus plumipes it is possible that the nano-scale filaments could lead to much stronger and longer lasting materials.
‘Studying this spider is giving us valuable insights into how it creates nano-scale filaments. If we could reproduce its neat trick of electro-spinning nano-fibres we could pave the way for a highly versatile and efficient new kind of polymer processing technology,’ said Professor Vollrath.