SCIENCE

Spiders use silk pulleys to pull prey 50 times larger

The researchers discovered how spiders make pulleys out of silk to pull large prey like lizards or small mammals from the ground below.

Previously, researchers did not know exactly how spiders capture large prey. This is the first time they have analyzed the construction and fabrication techniques of spider silk to trap and lift heavy animals. In fact, spiders often actively adjust the texture after catching prey, attaching pre-stretched strands to the pulley to maximize lift and lift prey much heavier than themselves. They published the research results on February 3 in the journal Royal Society Interface.

Spider silk is a very good energy dissipation material. When an insect is caught in a web, the energy from its struggling motion is absorbed and dissipated through the interconnected web of fibers. Spider silk is also elastic allowing for energy storage and magnification, like bowstring. In the study, scientists wonder how the web spun spider takes advantage of the elastic properties of the silk to lift heavy objects.

There are more than 2,200 species of spider webs described in the family Theridiidae. They live all over the world and are famous for thick, asymmetrical webs. In the study, the experts worked with two web spiders, Steatoda paykulliana and Steatoda triangulosa. They let them pull the orange-spotted cockroaches (Blaptica dubia) alive. The spider weighs 0.22 g and the heaviest cockroach is almost twice as large (0.56 g).

The team observed the spiders as they spread their webs, placing special sticky fibers to capture prey, and signaling when an object is attached. If the unlucky victim is a small insect, a single strand of silk is enough to lift it, says team leader Gabriele Greco, a postdoctoral fellow at the University of Trento in Italy. But if the prey is too large, the trap changes.

No longer a passive observer, the spider begins to create super-stretch strands, which can attach one end to the web and the other to its prey. When relaxed, the filament releases stored energy to gradually pull up its prey. The spider repeats until it has pulled its prey to the desired height. At the end of the experiment, the spider is able to raise cockroaches 8 cm above the ground. Their fastest lifting speed is about 0.01 cm per second. Through this mechanism, Greco et al. Estimated that web spiders could pull prey up to 50 times heavier than them.

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