  Scaling networks of cosmic defects, such as strings and textures, actively
generate scalar, vector and tensor metric perturbations throughout the history
of the universe. In particular, {\em vector} modes sourced by defects are an
efficient source of the CMB B-mode polarization. We use the recently released
BICEP2 and POLARBEAR B-mode polarization spectra to constrain properties of a
wide range of different types of cosmic strings networks. We find that in order
for strings to provide a satisfactory fit on their own, the effective
inter-string distance needs to be extremely large -- spectra that fit the data
best are more representative of global strings and textures. When a local
string contribution is considered together with the inflationary B-mode
spectrum, the fit is improved. We discuss implications of these results for
theories that predict cosmic defects.
