The two most common rat species in North America are the Roof Rat and the Norway Rat. Roof Rats are a bit smaller, weighing 6-10 oz. and have an 8 inch body with an 8 inch tail. Roof Rats tend to live in warmer areas and inhabit areas above ground, such as in trees. Norway Rats weigh from 10-16 oz. and have a 9 inch body with a shorter tail. Norway Rats live in cooler climates and prefer to live at ground level. Neither species usually lives for more than a year in the wild. They can breed year-round and produce litters of up to 10 young around 5 times per year. Both will eat a wide variety of foods and are considered pests for many reasons; the main one being their tendency to spread disease.