When we think of the ways spiders use their silk, the image of a dusty spiderweb littered with encapsulated bugs usually comes to mind. But unlike this hackneyed image, Tangle Web Spiders use their silk for a rather interesting purpose: to lift.
What are they?
Tangle-web spiders, part of the Theridiidae family, get their name from the sporatic bundles of webbing they call their home. This group is the host of a plethora of species, including the notorious black widow. As their net-like webs wait for prey to be caught, long lines of sticky silk are connected to the ground. When small prey runs into these anchored lines, the silk will disconnect from the ground, spring up and capture it. With this automated process there is no need for the spider to lift the prey itself. But what about larger prey? This is where the ingenuity of the spiders comes to light. Instead of waiting for the large prey to run off, these spiders will actually slowly lift their prey off the ground, impeding their movement.
Last week, a study of this process was published in the Journal of the Royal Society Interface. It was conducted by taking using five spiders, one false black widow spider and four triangulate cobweb spiders, and placing them in a closed black box. Researchers then introduced orange-spotted roaches, a cockroach from Central and South America, into the boxes, which were up to 50 times the size of the spiders. Afterwards, the researchers observed and documented how the prey was lifted, paralyzed then eaten by the tiny creatures.
How does it work?
Impeding the movement of the prey is the key motive of lifting them. But this is not something these spiders can do with their stregnth alone. Instead, they rely on their silk. Spider silk is a facinating material. It can behave as strong as steel but also as elastic as rubber. This elasticicy is simmilar to the bow of a bowstring, which can be pulled taut then released to shoot an arrow great distances.
The Tangle Web spiders use this concept to lift their prey. They attach hypertense threads of elastic silk from their web to their prey. Much like a bowstring, it contracts and exert a force which incrementally pull the prey upwards. This process is repeated until the desired height. As you might imagine this process is very slow. The fastest recorded velocity was 0.0046 cm/s−1. During this slow process, the prey did try to escape, but due to the slack of the lines of silk after they contracted, it did not snap.
After leaning more about these spiders, I can say that I was once again amazed wonders of the natural world. All around us we are surrounded by creatures with astaunding capabilities and inginuety. These small spiders overcame physical barriers and lifted objects 50x their own weight using merely their silk. Now, I am only left to wonder what other facinating creatures lie unbeknownsted to me, and what astonishing feats they can accomplish.