Hanging by many tails: Collective underwater breathing in entangled aquatic worms *

Many aquatic organisms leverage hydrophobic and hydrophilic body structures to live above and below the water surface. In this talk, we will discuss how California blackworms (Lumbriculus variegatus) use their tails to collectively breath underwater. Typically, these worms burrow and anchor their heads into granular substrates while simultaneously lifting their tails up vertically. The tail, which is used for gas exchange, forms a right angle as it reaches the air-water interface. Due to its material nature, these tails break water surface tension, allowing a worm to “latch” and hang freely onto the surface. In the absence of substrates, individuals instead form a physically entangled “blob” and utilizes this emergent structure as an anchor. We discover that as more blackworms latch onto the surface and entangle together, they can collectively lift off the ground and float, essentially creating a “worm buoy”. We hypothesize that this conformation allows smaller worms to reach the surface for respiration. Additionally, we discover a complex system of alternating hydrophobic segments and hydrophilic intersegments on the tails that facilitate this interfacial latching and unlatching, which we validate with simple physical models and force measurements.