The brown rat is an extremely invasive species—a pest, that survive on human-produced garbage, usually, but often times this nasty rodent will help themselves to food meant for human consumption. Rats also carry disease. Throughout history rodent-borne diseases have caused more human death than any other epidemics on earth.
For centuries, humans have been raging a losing war against rats. In the 1930s, New York City officials tried to rid the city of its rats with mustard gas, then with a powerful anticoagulant ten years later, and again with DDT during the 1970s. Nothing worked. Then last year, the city earmarked $32 million on yet another rat eradication program. Likewise, New Zealand has vouched to make the entire archipelago rat-free by 2050.