The Biology of the Norway Rat

The Norway rat is a rodent which is stocky and it burrows. It was introduced in America by settlers from Europe. This is a rat that spreads so quickly and easily throughout many areas. It is generally found at the lower elevations and can be found in almost any place where humans live.

This rat is also often referred to as the barn rat, house rat, brown rat, wharf ray and gray rat, and it is a bit larger than the roof rat. It has a blunt nose and small ears. The ears are close set and they don’t reach the eyes if pulled down. The tail is rather scaly and semi naked in its nature as compared to the rest of the body. Its tail doesn’t reach beyond its ears, and on average the adult will be around one pound. The fur is coarse and is usually reddish gray or brownish. It has a belly that is whitish gray. There are some rats that are blackish.


These rats live in very close association with people. They can burrow and create nests under structures and buildings. They can create a home under corner slabs, at the banks of streams, around ponds, in garbage dumps and all other areas where they can find shelter, water and food. When in the rural setting, they live in kennels, silos, buildings, granaries and barns. In the urban and suburban areas, they live in the residences and around them as well as in sewers, docks, slaughterhouses, stores, warehouses and cellars. They can climb but they prefer the lower floors even in multi-story buildings.

Their diet

The rats can eat basically any food type. When they have a choice, they will select a diet that is nutritionally balanced. They prefer fruits, nuts, fish, meat, and even cereal grains. They require ½ to 1 ounce of water in a day when they eat the dry foods, but much less is required when the diet is balanced. This is to satisfy their need for moisture.

Biology, behavior and reproduction

Primarily, the Norway rats are nocturnal. They become active at dusk and then they start seeking water and food. There are some rats that can be active in the daylight, especially where the populations are rather high. You will also see them in the daylight when there is construction or there are changes in the weather. They have poor eyesight but have an amazing sense of taste, smell and touch. Their clutters are born after 21-23 days and may come in groups of 6-12 young ones. They are born with no fur and with their eyes closed.

Go back to the How to Get Rid of Rats page or email us if you have any other questions about The Biology of the Norway Rat