The Roof Rat found commonly in Central California is the same species (Rattus rattus) as the Black rat.
The black rat is a common long-tailed rodent of the genus Rattus (rats) in the subfamily Murinae (murine rodents). The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 1st century and spreading with Europeans across the world.
A typical adult black rat is 12.75–18.25 inches long, including a 6.5–10 inch tail, and weighs 4–12 oz. Despite its name, the black rat exhibits several colour forms. It is usually black to light brown in colour with a lighter underside. In the 1920s in England, several variations were bred and shown alongside domesticated brown rats. This included an unusual green tinted variety. The black rat also has a scraggly coat of black fur, and is slightly smaller than the brown (Norway) rat.
Black rats (or their ectoparasites) are able to carry a number of pathogens,of which bubonic plague (via the rat flea), typhus, Weil’s disease, toxoplasmosis and trichinosis are the best known.