  We derive a general formula for the inertialess dynamics of active particles
in linear viscoelastic fluids by means of a modified reciprocal theorem. We
then demonstrate that force-free active particles in Maxwell-like linear
viscoelastic fluids with no retardation have exactly the same dynamics as in
Newtonian fluids. In contrast, active particles in Jeffreys-like fluids with
retardation can display markedly different dynamics, including net motion under
reciprocal actuation thereby breaking the scallop theorem.
