Spider spins electrically charged silk
In their quest to make ultrastrong yet ultrasmall fibers, the polymer industry may soon take a lesson from Uloborus spiders. Uloborids (pictured) are cribellate spiders, meaning that instead of spinning wet, sticky webs to catch their prey, they produce a fluffy, charged, wool-like silk. A paper published online today in Biology Letters details the process for the first time. It all starts with the silk-producing cribellar gland. At 60 micrometers, it is among the smallest silk glands ever observed and is covered in microscopic spigots that produce a low-viscosity liquid silk. In contrast with other spiders, whose silk comes out of the gland intact, scientists were surprised to discover that uloborids’ silk is in a liquid state when it surfaces. As the spider yanks the silk from the duct, it solidifies into nanoscale filaments. This “violent hackling” has the effect of stretching and freezing the fibers into shape. It may even be responsible for increasing their strength, because filaments on the nanoscale become stronger as they are stretched. In order to endow the fibers with an electrostatic charge, the spider pulls them over a comblike plate located on its hind legs. (This also gives the thread its wool-like appearance.) The technique is not unlike the so-called hackling of flax stems over a metal brush in order to soften and prepare them for thread-spinning, but in the spider’s case it also gives them a charge. The electrostatic fibers are thought to attract prey to the web in the same way a towel pulled from the dryer is able to attract stray socks. Next, researchers plan to test the silk for strength, as natural silks offer advantages over synthetics in terms of toughness, processing efficiency, and environmental issues.