Norway Rat

Scientific Name: Rattus norvegicus
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Muridae
Genus: Rattus
Species: norvegicus

Rats! Most of North America would prefer not to have rats in their landscaping, homes and other structures, yet a great many people keep them as pets. This may seem to play on the individual preferences of people, but, in fact, the rats kept as pets are not the same species of rodent that moves into your property without signing a lease agreement! The Norway Rat, the Roof Rat and to a smaller extent the Woodrat are the most common pests found living and feeding in our homes and yards.

Rat Natural History

While woodrats are native to the continent the Roof rat and the Norway rat have been introduced by humans. It is assumed that these rodents traveled over in ships with the early settlers of North America. If you live in Hawaii you may have a problem with Polynesian rats as well.

Rat Physical Appearance

Norway rats are the largest of the introduced species. They can reach lengths of up to 18 inches including the tail. The tail itself ranges in length from six (6) to eight and one half (8 ½) inches and are conspicuously hairless. Brown and black coarse fur covers the majority of the animals with the undersides of the Norway rat are gray to yellow. The overall weight of these animals is only about one (1) pound. The Norway rat has a generally stocky appearance with a blunt nose and shorter ears.

Roof rats are a bit smaller than the Norway rats, save for their ears which are actually long enough to reach their eyes when folded over. Size wise, the Roof rats are much smaller. Weighing in at only one-half (1/2) of a pound. The tail of the Roof rat is longer than that of the Norway rat measuring almost as long as their body. Their coloring is brown with black on top of coarse fur and a belly that is more often than not white in hue. The nose of the Roof rat is pointed.

Young rats are often confused with house mice. To help distinguish between the two (2) take note of the size of the feet. Juvenile rats will present with very large feet in comparison to the rest of their body.

Woodrats are a little smaller than the introduced species of Roof and Norway. They can also be distinguished from them by way of their soft and fine fur, light colored feed and most importantly, their fur covered tails.

Rat Behavior

Rats are nocturnal and very curious. They spend most nights constantly exploring their surroundings. They memorize their pathways that led them food and shelter earlier. Rats are exceptionally apprehensive of new things in they may find in a well traveled pathway (this makes trapping a more difficult task).

Rats are prolific breeders. The time between conception and birth is very short, only 21 to 23 days. Females give birth to six (6) to twelve (12) babies at one time. Once the babies are born the females are ready to conceive again within two (2) days after a litter is born! Breeding itself will become more prevalent in the spring and fall. On average, however, a female rat will give birth to four (4) to six (6) litters per year. Baby rats are born hairless with closed eyes but are nearly independent within three (3) weeks which allows for the mothers to prepare to give birth to another, possibly twelve (12) new babies! These newborns are even ready to breed themselves at three (3) months of age. Rats normally live only to 12 months of age, but some may live as long as eighteen months.

As with most nocturnal animals, the eyesight of rats is less than ideal. They rely primarily on a keen sense of smell, taste, hearing and touch. Their intense sense of smell is what leads these rodents into our homes. Rats are great swimmers and they will follow the scent of your dinner through your drains into the sewer systems where some rats will live. They follow this scent through the pipes and into your home via your toilet! Their long whiskers are used as sensitive tactile sensors. They use them for purposes of travel, detecting walls in the darkness as well as burrow barriers.

Roof rats are more agile climbers while Norway rats are more powerful swimmers and jumpers. This means that while they may live in the same building, Roof rats will occupy the attic areas while Norway rats will be more comfortable in the basement. Despite the fact that they live in close quarters, Norway and roof rats are not friendly. The Norway rat will kill Roof rats that it finds in its territory.

Woodrats are known by many as “pack rats”. They have a tendency to take and hide small shiny objects such as jewelry, forks and spoons.

Rat Benefits & Detriments to Humans and the Ecosystem

Rats are well known for many detriments to humans. At the forefront of these detriments is the fact that rats carry the plague virus. They also carry tetanus, leprosy, trichinosis, and salmonella. This prevalence for disease leads to rats, Norway and Roof, contaminating food sources just by feeding off of them, e.g. your grain and feed stocks.

As far as structural damage rats can do great harm. This includes damage done by gnawing and burrowing in and around foundations for homes and other structures. They will gnaw on electrical wires, wood framing along doorways, windows, and even do damage to metal structures! Rats cause problems to humans by tearing up insulation inside walls for use as nesting materials, too. Woodrats will tear up furniture and mattresses of campers and cars!