Rattus rattus, the black rat. Smaller than Rattus norvegicus, the brown rat, which later supplanted it, it is also keener to live near humankind. Timber houses and overcrowded slums provided excellent homes. The link between the rat as reservoir of infection and host to fleas which could transfer to man was not understood. Efforts were made to eliminate cats and dogs: if anything, this encouraged the rats. Body lice were also important plague vectors.