Physics of Pressure-Driven Eversion by Bloodworm

When you take off your socks, they often turn inside out. This process is called eversion, and many animals utilize eversion for various purposes. Bloodworms (Glycera dibranchiata) possess an eversible proboscis, normally concealed within their bodies, that extends outward to attack prey or burrow through soil. We model the bloodworm as a pneumatic system, where contraction of circular muscles elevates internal pressure, initiating eversion. By conducting tensile tests on bloodworm tissues, we assess the safety factor of the operating pressure to the maximum sustainable pressure. Through kinematic analysis of bloodworm eversion and dimensionless comparisons with other species, we investigate how skin thickness and material properties prevent rupture under critical pressures.