Living Knotoids

Despite lacking limbs, creatures like worms, eels, and snakes have devised various methods to perform tasks typically associated with limbs, such as gripping and grooming. A particularly fascinating strategy they use is knotting their flexible bodies. Although this behavior is observed, the mechanisms enabling these organisms to tie and untie knots without becoming irreversibly tangled are not yet fully understood. In our research, we investigate this knotting phenomenon using the California blackworm (Lumbriculus variegatus) as a model organism. Under laboratory conditions, we observed that these worms spontaneously form knots ranging from simple overhand knots with three crossings to more complex structures with up to six crossings. To understand the mechanics behind their rapid unknotting actions—occurring in less than a second in response to acute stress—we employed high-speed videography. Subsequently, we conducted behavioral experiments to identify potential triggers for knot formation. These assays involved situations where the worms removed debris from their bodies or were exposed to high turbulence in their aquatic environment. Through this study, we aim to contribute to a broader understanding of knotting behavior across various limbless organisms, spanning six orders of magnitude in size—from microscopic bacteria to large pythons.