British Spider Spins Unusual Web
(Inside Science) -- A type of spider commonly found in British retail nurseries has a unique way of spinning its web, according to research by a team of arachnid specialists.
The spider, whose formal name is Uloborus plumipes, starts by spinning silk filaments much thinner than those created by other spiders. Then, instead of relying only on the sticky, glue-like substance lining the silk to ensnare its prey, this spider charges the filaments electrostatically by combing them vigorously with its back legs.
The team at Oxford University's Oxford Silk Group that observed the details of the unusual process hopes to use the understanding of the process to develop improved materials.
"If we could reproduce [the spider's] neat trick of electro-spinning nano-fibers we could pave the way for a highly-versatile and efficient new kind of polymer processing technology," said Fritz Vollrath, who heads the group.
Polymers created that way could potentially find use in such tasks as wound healing, tissue engineering and environmental monitoring, he added.
The use of electrostic attraction to complement the glue on spiders' webs, thereby permitting the webs to catch everything from pollen and pollutants to flying insects, is not unusual.
"Generally, silk is an insulator, but specific silks like the 'wet glue silk' of the more modern spider can charge up [electrically]," Vollrath said.
However, the electrostatic effect in Uloborus plumipes is significantly larger than in many other spiders. That stems in part from the fact that the creature creates its web by spinning silk filaments much thinner than those of other spiders. The filaments are about 50 nanometers in diameter, more than 100 times thinner than the several-micrometer diameter of most spiders' silk.
Uloborus, found mainly in the Southeast England, is an example of so-called cribellate spiders. These spiders use an organ called the cribellum, lacking in most types of spider, to create ultrathin, puffy fibers. Prey insects typically become entgangled in the fibers in a web, allowing the spider to bite them at leisure.
For their research project, Vollrath and his colleague Kristin Kronenberger used adult female Uloborus spiders collected in heated, pesticide-free nurseries in Hampshire, a county southwest of London.
In the laboratory, they first took photos and videos of the spiders spinning their silk, to study the nature of the organs responsible for the process and how they carried out their task.
"We studied the functional morphology of the internal silk gland processing system in addition to the actual spinning behavior," Vollrath said.
To zero in on the organs the spiders use to make their filaments, the pair relied on three different types of microscopy, including two types of light-based microscopes, as well as electron microscopes.
"It's like zooming in on Google Earth view," Kronenberger explained.
The studies revealed close-up details of the spider's cribellum. This is an extrusion system that creates long threads of material by squeezing it through a small opening. It consists of a multitude of tiny glands, each of which ends in extremely long, narrow, and uniquely shaped outlets for the silk spun in the organ. The outlets, or spigots, are about 500 nanometers in length and roughly 50 nanometers wide at their exit points.
A nanometer is one-billionth of a meter. A human hair typically has a diameter of 50,000 to 100,000 nanometers. A human fingernail takes about a minute to grow 50 nanometers longer.
"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," Kronenberger said.
Having spun its silk, the observations revealed, the spider sets out to give it the stickiness it needs to capture its prey.
"The swath 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," Vollrath explained. "When it comes to the 'dry' cribellum silk, it appears that Uloborus charges up sections -- the puffs -- of the insulator, the capture thread."
Several parts of the process are unique.
"The spinning system [we] observed has key features not found in other spiders studied so far and clearly presents a challenge that needs to be tackled in detailed follow-up studies," the pair report in Biology Letters, a journal published by the United Kingdom’s Royal Society.
Part of that challenge consists of expanding observations to other types of cribellate spider. The two researchers "only presented detailed images of the silk production system of Uloborus plumipes," said Victor Ortega-Jimenez of the University of California, Berkeley. "Future measurements or modeling of the electrical, viscous, and capillary forces involved during silk production of cribellate spiders are required to understand this curious production process."
The Oxford team, meanwhile, will also focus on practical applications of the fresh understanding that might lead to new materials for human use.
"Conventionally, synthetic polymers fibers are produced by hot-melt extrusion; these typically have diameters of 10 micrometers (10 millionths of a meter) or above," Vollrath said. "But technology that could enable the commercial production of nano-scale filaments would make it possible to manufacture stronger and longer fibers."