Some spiders take on prey that is much larger than them, including lizards. To prevent their prey from running away, they use their nets as pulleys to lift the doomed animals off the ground.
Gabriele Greco and Nicola Pugno of the University of Trento, Italy, used high-speed video to observe five captive spiders from the Theridiidae family – the most common type of spider in human homes – that catch cockroaches up to 50 times as massively as they do themselves. They found that the spiders appeared to be using their body weight to stretch the silk threads to keep them taut before they were attached to the cockroaches. The spiders then attached more and more threads to their prey until it was lifted into the air.
“In the end, all of these threads create enough tension to lift the prey, and then the spider wins,” says Greco. “Then the prey cannot escape because it cannot grip the surface underneath.” Once the prey is off the ground and unable to run away, the spider can take its time to kill and devour it.
The researchers found that the silk did not stretch much when it was lifted, possibly because the spiders had already stretched it out before attaching it to their prey. This allowed the threads to recover when the cockroaches fought, rather than sagging permanently. “This silk that was used to lift the prey is very strong, like steel, but it’s just as elastic as the normal silk you would use to make clothes,” says Greco.
This is interesting because you couldn’t expect such a relatively simple animal to know how to use tools to capture its prey in such ingenious ways, he says. It can allow spiders to have an oversized impact on their ecosystems by eating all kinds of small animals rather than just insects.
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