Measuring the 3D hydrodynamics of swimming snakes *

Snakes are anguilliform swimmers. Although the hydrodynamics of anguilliform swimming can be predicted through idealized numerical models, they are yet to be observed in three dimensions. 

We used volumetric 3-component velocimetry (V3V) to capture the instantaneous 3D wake structure of two female and one male freely swimming dice snakes (Natrix tessellata).

We observed that the wake topology after a tailbeat cycle is a hairpin-like, curved-shaped head vortex street. We compare quantitatively different sequences of the same individual and of different individuals using slices of the velocity field in the wake of the snake. 

These results are a first step towards the understanding of the efficiency of anguilliform swimming and will be compared to results for other species of aquatic snakes that have independently evolved an aquatic life-style. This may help future developments of  bio-inspired aquatic systems.