Worms that create intricate, tangled blobs with their bodies can disentangle in milliseconds when threatened. This speedy unscrambling is possible because each worm wriggles in a special corkscrew motion.
California blackworms (Lumbriculus variegatus) tangle their bodies into knotted “worm blobs” to preserve moisture during droughts. In the wild, these balls can contain up to 50,000 worms. It takes the animals a few minutes to form a blob, but when Harry Tuazon at the Georgia Institute of Technology shined ultraviolet (UV) light on one of these twisted-up worm balls in the lab he was shocked to see the worms disentangle in just a few tens of milliseconds.
He and his colleagues wanted to understand how the worms were extricating themselves from the blob a hundred times more quickly than they formed it. They used ultrasound to look inside blobs of about 20 worms and determine the details of their structure, such as how many times each worm coiled around another. To do this, they encased the blob in gelatine so the worms would wriggle less. Next, they put the blob in a shallow container of water, scared the worms with electric shocks or UV light and then filmed the rapid disentangling, with researchers manually tracking the trajectory of each animal’s head.
The team also collaborated with mathematicians who specialise in the theory of knots. These researchers used data from the observations to construct a mathematical model and run computer simulations, which revealed that the key difference between the worms’ slow entangling and rapid disentangling was the direction in which each animal performed a type of helical wriggle.
Repeating a corkscrew motion in one direction for a while and then abruptly switching directions leads to tangling, but quickly alternating between corkscrewing left and right efficiently disentangles the blob, says Vishal Patil at Stanford University in California.
“I would have thought that, mathematically, disentangling isn’t really a solvable problem because it’s so complex, but then Harry and colleagues showed us these videos and it was like, if worms can solve this problem, so can we,” he says.
This new understanding of how blackworms morph from a tight blob to being more dispersed may help researchers eventually achieve the “dream of creating a material that can do stuff by itself” says Antoine Deblais at the University of Amsterdam in the Netherlands. In the future, materials made from tangled soft filaments could become looser and more bendable, or harder and more compact, if those filaments could be made to wriggle like the worms, he says.