Rats (Rattus spp.) have caused more human suffering and more economic damage than any other vertebrate pest. From causing plague epidemics (the "Black Death" of Europe) to rat-bite fever, whether feeding on stored grain or gnawing electric wires, rats are enemies of humankind. Statisticians estimate that rats destroy 20 percent of the world's food supply every year by feeding, and indirectly through contamination.
In most instances, rats are very wary. Hundreds may be nesting in a city block-in underground burrows, in sewers, on roofs, inside buildings-with few people in the area realizing it. Within a population, some rats will be easy to control, some difficult.