  We study the representations of SU(2) lattice gauge theory in terms of sums
over the worldsheets of center vortices and Z2 electric strings, i.e. surfaces
which open on the Wilson loop. It is shown that in contrast to center vortices
the density of electric Z2 strings diverges in the continuum limit of the
theory independently of the gauge fixing, however, their contribution to the
Wilson loop yields physical string tension due to non-positivity of their
statistical weight in the path integral, which is in turn related to the
presence of Z2 topological monopoles in the theory.
