Carrier of fleas, and diseases. They are known to exhibit aggressive behavior toward other rat species, and human beings. They were responsible for the bubonic plague outbreak in the 1930's. Rats are known to transmit at least 35 deadly diseases.
There are two dominant species of rats, the Norwegian rat and the brown rat. They are more often heard than seen. The trail of feces or droppings they leave behind is a sure sign that they are close by. A rat's tail regulates its body temperature. When rats get too hot, they lay on their backs, so they can sweat from the soles of their feet. Rats eat smaller rodents for snacks, and their survival instincts lead them to hunt for fish and birds. Rats can mate in less than five seconds. Three to three and a half weeks after mating, they can give birth to a litter of up to 12 babies. The female species can produce up to six litters per year. Their need for water makes them vulnerable. However, they can consume one third of their body mass weight in food per day. The adult rats can reach a body weight up to 18 ounces or 1 1/2 pounds, and lengths reaching up to an estimated 18 inches, from head to toe. Under favorable conditions rats can live for 3 years; although, the oldest rat in the world died at the age of seven years old. Otherwise city rats, like the Norway rats, can survive for up to six months in a city environment. Rats can survive without food for two weeks, and when no food is available they will devour each other. Rats can swim 1/2 mile in the ocean, tread on water for 72 hours, and hold their breath underwater, for 15 minutes.