Interfacial Latch of Aquatic Worms

Many organisms inhabit the interface between air and water, known as the neuston, as a means of survival. An unexpected organism that may transition to the neuston is the California blackworm (Lumbriculus variegatus), which measures 2 to 4 cm in characteristic length, has a diameter of approximately 0.5 mm, and an apparent weight of 0.5 mg in water. Blackworms typically reside in oxygen-deprived conditions at the bottom of freshwater environments. While they primarily respire through their skin, they have a unique ability to enhance their oxygen supply by extending their tails toward the air-water interface. They generate a distinctive 90^o bend with their tails to increase contact with the water surface. When these worms gather in large groups, they form entangled clusters that float together. In this talk, we explore how blackworms remain suspended at the underside of the interface. We hypothesize that the tails generate sufficient surface tension keep the worms latched. Using established models for smooth, horizontally floating cylinders, we estimate that a blackworm's tail can support approximately 26 times of its apparent weight. We validate our model's predictions through experiments conducted with flexible plastic straws.