Watch out for flies and mosquitoes, here is the sling spider

Encountering an invisible spider web in the woods can be quite scary, but what if you had to worry about a spider web – and the spider – catapulting you? That’s what happens to insects in Peru’s Amazon rainforests, where a tiny slingshot spider throws a web – and itself – to catch unsuspecting flies and mosquitoes.

Researchers at the Georgia Institute of Technology have produced what may be the first kinematic study of how this incredible arachnid stores enough energy to produce an acceleration of 1,300 meters / second.²—100 times the acceleration of a cheetah. This acceleration produces speeds of 4 meters per second and subjects the spider to forces of around 130 Gs, more than 10 times what fighter pilots can withstand without fainting.

The Peruvian spider and its cousins ​​stand out among the arachnids for their ability to craft external tools – in this case, their webs – and use them as springs to create lightning-fast movement. Their ability to hold a spring ready to throw for hours while waiting for a mosquito to arrive suggests another amazing tool: a locking mechanism to release the spring.

“Unlike frogs, crickets or grasshoppers, the sling spider does not rely on its muscles to jump very quickly,” said Saad Bhamla, an assistant professor in the chemical and biomolecular engineering faculty at Georgia Tech who studies ultra organisms. -fast. “When weaving a new web every night, the spider creates a complex three-dimensional spring. If you compare this natural silk spring to carbon nanotubes or other man-made materials in terms of power density or energy density, those are orders of magnitude more powerful. “

The study, supported by the National Science Foundation and the National Geographic Society Foundation, was published on August 17 in the journal Current biology. Understanding how web silk stores energy could potentially provide new sources of energy for small robots and other devices, and lead to new applications for the rugged material, the researchers say.

Sling spiders, known by the scientific genus Theridiosomatid, build three-dimensional conical webs with a tension line attached to the center. The Peruvian member of this spider family, which is about 1 millimeter in length, pulls the tension line with its front legs to stretch the structure while clinging to the web with its rear legs. When it detects a meal within range, the spider launches the web and itself towards a fly or mosquito.

If the launch is successful, the spider quickly wraps its meal in silk. If the spider misses, it simply pulls the tension line to reset the web for the next occasion.

“We think this approach probably gives the spider the advantage of speed and surprise, and possibly even the effect of stunning the prey,” noted Symone Alexander, postdoctoral researcher in Bhamla’s lab. . “Spiders are tiny, and they prey on fast-flying insects that are bigger than they are. To catch one you have to be much, much faster than them.

Slingshot spiders were described in a 1932 publication and more recently by Jonathan Coddington, now a senior research entomologist at the Smithsonian Institution. Bhamla has an interest in small, fast organisms, so he and Alexander organized a trip to study the catapult creature using high-speed cameras to measure and record movement.

“We wanted to understand these super-fast movements because they can force our perspective to change from thinking that cheetahs and hawks are the only fast animals,” Bhamla said. “There are many very small invertebrates that are able to move quickly through unusual structures. We really wanted to understand how these spiders achieve this incredible acceleration.”

The researchers traveled six hours by boat from Puerto Maldonado to the Tambopata research center. There is no electricity in the area so the nights are very dark. “We looked up and saw a little red dot,” Bhamla recalls. “We were so far from the nearest light that the point turned out to be the planet Mars. We could also see the Milky Way so clearly.”

The intense darkness begs the question of how the spider detects its prey and determines where to go. Bhamla thinks he must use an acoustic sensing technique, a theory backed by how the researchers tricked the spider to throw its web: they simply snapped their fingers.

Beyond detection in the dark, researchers have also wondered how the spider triggers the web release. “If an insect is within range, the spider releases a small bundle of silk that it created by crawling along the tension line,” Alexander said. “Releasing the bundle controls how far the web travels. The spider and web move backwards.”

Another mystery is how the spider patiently holds the web while waiting for the food to pass. Alexander and Bhamla estimated that stretching the web requires at least 200 dynes, a huge amount of energy to be generated by a small spider. Holding this on for hours could waste a lot of energy.

“Generating 200 dynes would produce enormous forces on the spider’s tiny legs,” Bhamla said. “If the reward is a mosquito after three hours, is it worth it? We think the spider must use some kind of trick to lock its muscles like a latch so it doesn’t need to. to consume energy while waiting for hours. “

Beyond curiosity, why travel to Peru to study the creature? “The sling spider offers an example of active hunting instead of passive, wait for an insect to collide with the web strategy, revealing an additional new feature of spider silk,” Bhamla said. “Before that, we hadn’t thought of using silk as a really powerful spring.”

Another unintended benefit is changing attitudes towards spiders. Before the study, Alexander admits that she was afraid of spiders. Being surrounded by sling spiders in the Peruvian jungle – and seeing the amazing things they do – has changed that.

“In the rainforest at night, if you shine your flashlight, you quickly see that you are completely surrounded by spiders,” she says. “In my house, we no longer kill spiders. If they are scary and are in the wrong place, we safely move them to another place.

Alexander and Bhamla had hoped to return to Peru this summer, but those plans were interrupted by the coronavirus. They can’t wait to continue learning from the spider.

“Nature does a lot of things better than humans can, and nature has been doing them a lot longer,” she says. “Being in the field gives you a different perspective, not only of what nature does, but also of why it is necessary.”