  We conduct experiments with flexible swimmers to address the impact of fluid
viscoelasticity on their locomotion. The swimmers are composed of a magnetic
head actuated in rotation by a frequency-controlled magnetic field and a
flexible tail whose deformation leads to forward propulsion. We consider both
viscous Newtonian and glucose-based Boger fluids with similar viscosities. We
find that the elasticity of the fluid systematically enhances the locomotion
speed of the swimmer, and that this enhancement increases with Deborah number.
Using Particle Image Velocimetry to visualize the flow field, we find a
significant difference in the amount of shear between the rear and leading
parts of the swimmer head. We conjecture that viscoelastic normal stresses lead
to a net elastic forces in the swimming direction and thus a faster swimming
speed.
