Anyone who’s worked with messy headphones knows how difficult it is to untangle tangled cords. However, tight knots are not a problem for California flea beetles. These tiny worms put together thousands of twists to form a tight mass reminiscent of a forkful of struggling spaghetti. These tangles take minutes to form, but the entangled black worms are free to wriggle in milliseconds.
Scientists have finally put it right how these legless escape artists use only a simple collection of muscles and neurons to seamlessly break out of a tight tangle. Vishal Patil says:In a study published today in the journal chemistryPatil and his colleagues used mathematical simulations to identify the movements black worms use to rapidly untangle.
California croworms (only a few centimeters long)Lumbriculus variegatus) easy to overlook. However, these aquatic worms are a common grub for ornamental fish and have demonstrated strength in numbers. Together, they form masses that writhe like creature features. These tangles are tight, but the first signs of a predatory diving beetle cause the fleshy worms to writhe in all directions.
Harry Tuazon, now a Ph.D. in bioengineering, said students at Georgia Tech caught a glimpse of this near-instantaneous reaction when they observed a black worm wriggling on a Petri dish in the lab. “I pointed the UV light at the ball of worms and all of a sudden it exploded,” he says. “It was fascinating.”
Tuazon was engrossed in these worm balls and unraveled in tens of milliseconds (a fraction of a blink). He microscopically filmed the movements of individual worms, then gradually added animals to increase the complexity of the ball. To unlock the physics behind these worm nests, he teamed up with Patil, who was doing his PhD at the time. A student at the Massachusetts Institute of Technology, he specializes in the geometry of knots and other complex systems.
Patil noticed something interesting when he saw a microscope video of a single worm reacting to a small electric shock by Tuazon. When the worm responded to the stimulus, it would move her head clockwise, then reverse direction and repeat the rotation counterclockwise. This created a figure eight pattern known as an alternating spiral wave.
To create an accurate mathematical model of the worm’s spiral locomotion, Patil also needed to see how individual worms moved within the tangle. This proved difficult for Tuazon, as the wormball was surprisingly impenetrable. X-rays failed because the worm was submerged in water. Micro-computed tomography scans provided only low-resolution glimpses. Ultimately, Tuazon decided the team’s best bet was sound. He used an ultrasound machine to create an image of a swarm of live worms placed in gelatin.
Ultrasound images allowed researchers to plot more than 46,000 points of data on individual worm movements. Worms were in constant contact with other worms in the writhing mess. Patil and his colleagues created a mathematical model of worm movement and performed his 3D simulation of entanglement.
Researchers found that by employing alternating spiral walking movements, the worms were able to untangle seamlessly. They also found that a slightly modified motion in which the invertebrates corkscrew mostly in one direction helped create tangles. If you wind it in a direction, it creates tangles,” says Patil. “When the worm quickly switches between clockwise and counterclockwise, you get a disentangling motion.”
The versatility of this movement allows the worms to fine-tune the entanglement, according to Eleni Panajitou, a mathematician at Arizona State University who studies the effects of entanglement in physical systems. “California Blackworm” [exhibit] Panajitou was not involved in the new research, but has written a related Perspective. chemistryToo much twisting will make the tangle too tight and the worm will lose its ability to escape. If you don’t twist it enough, the protective tangles won’t form.
She thinks similar movements can help undo a series of intricate knots that are ubiquitous in both the natural and man-made worlds. It occurs naturally in everything from coiled DNA strands. Humans have long used tangles to make ropes and weave cloth. “Researchers are not only trying to explain what nature is doing with these worms, but also mapping their potential in other systems and situations,” says Panajitou.
The team believes these worm movements could help researchers program string-like filaments in soft robotic systems to actively change shape. This could create flexible bandages that change shape as wounds heal, or water filters that can be fine-tuned to screen out specific particles.
Patil thinks the evidence is in the worm mass. “These worms have given us general principles for entangling and untangling and could be a toolbox for manipulating other systems,” he says. “We know worms can do it, so it’s not just a mathematical model.”
