The rapid urbanization of Houston, TX, creates the ideal breeding ground for commensal rodents like Norway rats and roof rats. In large cities, they thrive on human activity while spreading diseases like leptospirosis, tularemia, Hantavirus, and plague. The city's extensive sewer system and many bayous allow rats in Houston to breed undisturbed before beginning their vertical migration from the sewers to the streets and buildings above. Once inside homes, they gnaw on wooden beams and wiring in walls, causing structural damage and the risk of electrical fire. Rat infestations can also be heard at night in the attic making scratching sounds.