  The effect of perturbations of electroweak strings on quark zero modes is
studied in 2+1 and 3+1 dimensions. As first discovered by Naculich, it is found
that the bosonic perturbations that destabilize the string give a mass to the
zero modes and also lift their degeneracy. The effect of the zero modes on the
stability of the string is discussed qualitatively and we argue that the
fermionic vacuum instability found by Naculich should lead to a distortion of
the bosonic string but not be responsible for decay.
