We suggest several reciprocal swimming mechanisms that lead to locomotion only in
viscoelastic fluids. In the first situation, we consider a three-sphere microswimmer with a
difference in oscillation amplitudes for the two arms. In the second situation, we consider a
three-sphere microswimmer in which one of the frequencies of the arm motion is twice as
large as the other one. In the third situation, we consider a two-sphere microswimmer with a
difference in size for the two spheres. In all these three cases, the average velocity is …