Video captures the cunning way spiders catch massive prey
Spiders "use their silks as external tools to overcome muscle limits."
From Spiderman's villain-catching webs to Shelob's terrifying cocoon, spider silk has long been a fixture of pop culture. Its strength captures our imagination, like a bug in a cobweb.
New research suggests these exaggerated pop culture depictions aren't so far from reality. Using their webs and a technique known as "lifting hunting," spiders really can trap foes up to 50 times heavier than themselves.
A new study published in the Journal of the Royal Society Interface describes spiders in the Theridiidae family. These critters use a unique "pulley" system of numerous silk threads — known as a tangle web — to lift their prey up to a height difficult to escape.
This research is yet "another example of how spiders use their silks as external tools to overcome muscle limits," co-author Gabriele Greco tells Inverse. Greco is a researcher in the engineering department at the University of Trento in Italy.
A spider capturing a large cockroach using a "pulley" system.
How they did it — Greco and co-author Nicola M. Pugno studied five different spiders from two species in the Theridiidae family: Steatoda paykulliana and Steatodatriangulosa.
The researchers placed each spider specimen in a plastic box at room temperature covered in black paper. Black paper was used so they could better see the spider's light silk strands.
For prey, the researchers selected a cockroach (Blaptica dubia) from South and Central America. This foe was chosen for its weight and size. Once released into the box, the scientists pressed record, and observed the ensuing battle.
A figure from the study explaining how the spider lifts large prey.
What's new — The purpose of the lifting hunt mechanism is to keep prey from escaping. What matters most is the "vertical component of the motion of the prey," the scientists write.
This became obvious in the evaluation of the recorded spiders.
Each prey capture involved wrapping a cockroach in spider silk. Then, the successful spider would attach additional "pre-stretched" silk threads to the cockroach in order to trap and lift it. These silk threads are produced by the major ampullate gland in the spider's body.
"Every time that the spider attaches a thread to the prey, it pre-stretches it," Greco says. He likens the mechanism to stretching an elastic band, which can be stretched a lot — or not a lot at all. The silk threads come pre-stretched and ready-made to ensnare the large prey.
It's not a quick catch. To perform the "deadlift," spiders travel up and down several times to add additional threads. This eventually creates a pulley mechanism allowing the spider to lift the cockroach higher and higher, not unlike an old-fashioned elevator pulley.
Only by applying a certain number of additional silk threads could the spider capture and lift. the cockroach. The spider also uses its venom to immobilize the prey, making the lifting process easier.
The scientists considered the prey "captured" if the spider managed to lift it close to the height of the main portion of the tangle web, located near the spider's den.
A figure from the study showing the physics of the spider's "pulley" mechanism.
Why it matters — This is the first time researchers observed spiders capturing such large prey in a controlled laboratory setting.
It was previously assumed spiders capture smaller prey using the elastic energy in "gumfoot threads," spring-loaded traps that suspend insects in the air.
But this mechanism doesn't work on larger prey like mice or snakes. Spiders lack the muscles to naturally lift prey much larger than themselves.
Think about it this way: Even a trained athlete who weighs 220 pounds can only bench press 380 pounds.
Spiders use the tangle web's pulley system to get over this hurdle. It enables them to get the most out of the elastic strength of the silk and capture massive prey using a multi-step method.
What's next — This study is a unique look into spider evolution. The ability to use a tool to overcome muscle limits is a novel one — and allows these spiders to dine on large, nutrient-packed meals.
However, research on this topic is limited, Greco says. To really understand the role these hunters play in our ecosystem, more studies are necessary. In the meantime, we can be glad we're too big even for a powerlifting spider.
Abstract: The spiders of Theridiidae’s family display a peculiar behaviour when they hunt extremely large prey. They lift the quarry, making it unable to escape, by attaching pre-tensioned silk threads to it. In this work, we analysed forthe first time in the laboratory the lifting hunting mechanism and, in order to quantify the phenomenon, we applied the lifting mechanics theory. The comparison between the experiments and the theory suggests that, during the process, spider does not stretch the silk too much by keeping it in the linear elastic regime. We thus report here 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.
