The Rat

Some urban animals live in such close proximity to people that they share food, a characteristic biologists call commensal behavior. The common rat (also called the Norway or brown rat) heads the list of commensal species. From their homes in basements, sewers, and trash piles, they go after anything people eat. Rats rarely starve.

For as long as history has been recorded, rats have lived in cities. Biologists believe these animals originated in the wilds of northern China. They stowed away on ships traveling from Asia to Europe in the Middle Ages and hitchhiked to the Americas with European colonists. Burrowers by nature, rats can gnaw through brick, concrete, wood, and metal, and they can squeeze through small spaces. Female rats breed all year long, except during periods of severely cold weather, producing litters of six in less than a month. In a year's time, a female and her offspring can produce 1,500 rats. Dogs, large cats, and human exterminators kill some of them, but no natural predator has evolved in cities to control the rat population. The best defense is to keep alleys and basements clean.