Mongoose. Brought to kill rats in sugar plantations in Puerto Rico and Hawaii in the 1800s. Now they’re destroying native birds, amphibians, and reptiles that would have been beneficial for pest control. 12 species of reptiles and amphibians have been driven extinct by mongooses, which also carry rabies and leptospirosis.
Rats. The United States has over a billion rats (mainly introduced Rattus rattus a.k.a European, black, or tree rat) and ratus norvegicus (Norway or brown rat). Poultry and other farms have about 1 billion rats, and urban and suburban areas have about 1 rat per human. Rats cause fires by gnawing on electric wires, polluting food, and carrying diseases.
Cats. About 200 million birds are killed a year by America’s 63 million domestic cats and 30 million feral cats.
Dogs. They bite around 4.7 million people a year, sending 800,000 to emergency rooms. Wild dogs in Florida, Texas, and other states harm far more livestock than wolves or coyotes, about $10 million in damage per year.
English sparrow. Eats crops, displaces native birds, carries 29 diseases that affect humans and domestic animals, plus the canker worms that invade gardens.
Jan 26, 1999. Alien Animals, Plants And Microbes Cost U.S. $123 Billion A Year, Cornell Ecologists Report. Science Daily