  Certain defense mechanisms of phages against the immune system of their
bacterial host rely on cooperation of phages. Motivated by this example we
analyse invasion probabilities of cooperative parasites in host populations
that are moderately structured. More precisely we assume that hosts are
arranged on the vertices of a configuration model and that offspring of
parasites move to nearest neighbours sites to infect new hosts. We consider
parasites that generate many offspring at reproduction, but do this (usually)
only when infecting a host simultaneously. In this regime we identify and
analyse the spatial scale of the population structure at which invasion of
parasites turns from being an unlikely to an highly probable event.
