Tiny Spiders Use Silk Web as Pulley To Lift Prey 50 Times Their Weight

The silk-spinning engineers use a mechanism similar to those in old-school elevator pulleys.
Derya Ozdemir

It is long known that spider silk is super strong: Tiny spiders can be seen lifting preys that are multiple times their weight; however, exactly how they manage to do that wasn't exactly clear.

Now, a new study published in the Journal of the Royal Society Interface has provided the answers after studying five different spiders from two species of the Theridiidae spider, Steatoda paykulliana and Steatodatriangulosa, to learn how the 'tangle web' acts as a pulley and the lifting mechanics that come with it.

The silk-spinning engineers

The study, which the researchers say marks the first time the lifting systems of spiders were studied in this particular way, has revealed a fascinating look into the spiders' silk-spinning techniques. The researchers placed a spider and a cockroach in a clear plastic box to capture this unique moment.

What they saw was this: The tiny spiders were able to lift their prey to an inescapable height by making a pulley system out of silk threads called a 'tangle web.'

The spiders first immobilized their prey by covering them in silk and envenomating them. This made sure the prey wouldn't wriggle to escape once they were lifted into the air. Then, they released a slightly different type of silk from their ampullate gland. The difference was that this type of skill could be used as it was or stretched like an elastic band. 

The researchers found that as the spiders began to build the tangle web, they only used this special silk which was pre-stretched to stick to the prey. Then, the spiders would run up and down the tangle web to connect more and more pre-stretched threads. After one point, the pre-stretched threads would become so elastic that they could achieve lift just like elastic bands, making it easier for the spiders to lift their prey. The researchers say that this mechanism is very similar to those seen in old-school elevator pulleys.

You can watch the spider-on-cockroach action below — or perhaps pass this one if you have arachnophobia

These findings, per the study,  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."

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