Electric thread-spinning spiders

While they may be one of the most hated and feared animals on the planet, there’s no denying that spiders are brilliant architects, capable of spinning some amazingly intricate and sometimes seemingly impossible webs. Some spiders even spin electrically charged silk filaments on the nano-scale, but how precisely they achieve this has eluded scientists.

Now, scientists have finally managed to detail some of the mechanisms that such spiders employ to produce these remarkable webs. Alongside furthering our knowledge of this fascinating process, scientists are hopeful that the discovery could help with the development of technologies that would allow the commercial production of nano-scale fibers. The study can be found in the journal Biology Letters.

Not all spiders spin webs, but those that do have evolved two very different mechanisms to capture and hold onto their prey with them. Some use a more ancient technique which involves spinning dry threads composed of thousands of electrically charged, nano-thin filaments, whereas others adorn their webs with sticky globs of glue. Since the majority of spider threads are on the micrometer scale, the ability to produce nano-scale fibers has long intrigued scientists, and now we are finally beginning to understand how they do it.

For the latest study, researchers from the University of Oxford studied the cribellate orb spider Uloborus plumipes, also known as the feather-legged lace weaver. Their name derives from the fact that they possess an ancient silk-spinning organ called the cribellum. These organs consist of one or more plates peppered with hundreds, sometimes thousands of long, narrow ducts known as spigots which average just 50 nanometers in diameter.

To unravel the spiders’ spinning secrets, the team started off by taking photographs and videos of the animals in action. Next, they used three different microscopic techniques, including two types of electron microscopy, to examine each specimen’s cribellum. Uloborus spiders possess some of the world’s smallest silk glands so far documented, measuring a mere 60 micrometers. “It’s these that yield the ultra-fine ‘catching wool’ of its prey capture thread,” first author Katrin Kronenberger explained in a news release.

Interestingly, they found that the cribellate silk remains liquid until the very last minute and only solidifies into the nano-thin filaments when the spider begins to yank the raw material out of the ducts. As the spiders violently pull out the silk, it becomes ‘frozen’ into shape in a matter of milliseconds. Then, to give these fibers an electrostatic charge, the spider combs the threads over tiny hairs located on the hind legs. It is this charge that is responsible for the wool-like appearance of the threads and, in combination with the extreme thinness of the fibers, provides Van der Waals forces that help capture and hold onto prey.

Alongside providing scientists with novel insights into how these spiders produce these nano-thin filaments, the researchers are hopeful that understanding the process will eventually enable scientists to reproduce it. If this is possible, it would allow the production of nano-scale filaments which could help scientists develop stronger, more versatile fibers.