Depending on your persuasion, images of spiders lifting prey seemingly far superior in size to them will either impress or terrify you (anyone remember huntsman vs possum?). Spider silk is famously strong, but even armed with a nylon rope most of us would struggle to pull a bison up onto a ledge, so how do little spiders do it?
New research published in the Journal of the Royal Society Interface has solved this puzzle after studying the hoisting power of five different spiders from two species of the Theridiidae spider: Steatoda paykulliana and Steatodatriangulosa. By watching the web slingers in action, they realized that these tiny engineers were able to lift prey to an inescapable height by creating a pulley system made up of many threads called a tangle web.
Co-authors Gabriele Greco and Nicola M. Pugno placed a spider and a cockroach (Blaptica dubia) in a plastic box-come-Thunderdome and recorded the ensuing drama. The box was lined with black paper to make it easier for the camera to pick up what was happening with the spiders’ light silk strings. The researchers say this is the first time the lifting mechanism of spiders has been studied in this way, and the novel approach revealed some pretty fascinating silk-spinning techniques.
The first step was to immobilize the prey Shelob-style by wrapping them in silk and envenomating them so they wouldn’t wriggle about as the arduous lifting process was completed. The spiders then released a slightly different type of silk that came from the major ampullate gland and, like an elastic band, could be used as it was or stretched. The recordings revealed that as the spiders began to build the tangle web, stretching from prey to a higher spot near the spider’s den, they only used this special silk, which was pre-stretched to attach to the prey.
Next came the heave, which saw the spiders running up and down the tangle web connecting more and more pre-stretched threads as it went. As these built in number, the elastic potential of the pre-stretched threads were able to achieve lift in the same way an elastic band snaps back to its smallest size when released. The mechanism is similar to that seen in old school elevator pulleys and made it easier for the spider to lift its prey with each additional thread. The battle was considered over once the cockroach had made it to the upper-most point of the tangle web close to the spider’s den.
“The spiders of Theridiidae's family display a peculiar behaviour when they hunt extremely large prey,” wrote the study authors. “They lift the quarry, making it unable to escape, by attaching pre-tensioned silk threads to it.” Understanding the mechanics of silk use is a vital avenue of research both for the innovation of novel technologies and materials, but also as a means of better understanding the evolution of silk spinners in general. The researchers state that their findings provide “further evidence for the strong role of silk in spiders' evolution, especially how spiders can stretch and use it as an external tool to overcome their muscles’ limits and capture prey with large mass, e.g. 50 times the spider's mass.”
The skillful manipulation of silk displayed by these tiny spiders demonstrates the transformative power of working smarter, not harder. If only the protagonists of The Gigantic Turnip had known.