It takes California blackworms—roughly 200 of which are pictured here—a few minutes to entangle themselves into a knotted ball to stay warm and moist but just milliseconds to untangle themselves and avoid danger. Georgia Tech’s Saad Bhamla and his colleagues now think they understand how the few-centimeter-long animals tangle and untangle themselves at such different rates. From an active-matter point of view, the worms are analogous to autonomous filaments. As individuals, they behave differently from how they function when they self-assemble into a larger emergent structure. With ultrasound imaging, the researchers observed that the three-dimensional motion of each worm follows a loop-like pattern. They approximated the movement with just two parameters involving a worm’s head: its turning speed and the rate at which it changes direction.
From those observations, the researchers developed a predictive model. In it, a dimensionless parameter called the chirality number describes the amount of right-handed or...
