Spiders use pre-stretched silk to lift prey from the ground

A pair of researchers from the University of Trento have found that some spiders use pre-stretched silk to lift prey from the ground. In their article published in Royal Society Interface Journal, Gabriele Greco and Nicola Pugno describe experiments with two species of spiders, Steatoda paykulliana and Steatodatriangulosa.

Previous research has shown that many types of spiders are capable of capturing prey that is much larger than they are – in some cases, 50 times as massive. But how they do it has not been well studied. In this new effort, the researchers conducted experiments in which they captured videos of spiders in boxes to uncover their secrets.

The boxes were just large enough for the spiders to use as a stand for building websites. Each of the spiders in the experiments had time to build their web, then the researchers placed a large South American variety of cockroach in the box where it quickly became entangled in the lower part of the spider web. And that’s where the action started. The researchers found that the spiders repeatedly spun a length of silk, stretched it slightly, and then affixed one end to the cockroach’s body and the other to an upper part of the web. The spider used its own body weight to stretch the silk like a rubber band. As the spider attached more strands to the cockroach, it was eventually lifted entirely off the ground, making it impossible to escape. The spider then tied the cockroach in place, injected it with venom, and then waited for it to die so it could consume its meal.

Looking closely at the spider as it went about its business, the researchers found that the spiders pulled the strands of silk at just the right amount of tension – too much, and they would lose their elasticity, too little would mean wasted effort.

Researchers say this is the first time that spiders have been observed capturing much larger prey – and it also demonstrates another way that spiders use webs to overcome their relatively small and light bodies to capture large prey.

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