Norway Rats (Rattus norvegicus)
Norway rats are also known as the brown rat, and sewer rat. This is the common rat found in Ohio. The other rat known for infesting homes is the roof rat (Rattus rattus). This rodent does not inhabit our region. It is a known pest in the South East States, and along the Pacific coast.
Once they are 2.5- 3 months of age, they begin breeding. The gestation period is 21-25 days. Litter sizes range from 6-14 pups, with an average size of 10 pups.. Females live about 5-6 months in the wild, but can live to be 1 year old. In most instances a female produces 3-6 litters in her lifetime. Breeding peaks during spring and fall.
An average length for a sewer rat is 16-18” including a 7” tail. An adult weighs from 7-18 ounces. The largest rat was 44 ounces! Their fur is shaggy and brown, with scattered black. Their sight is poor. Additionally they are color blind and cannot see past several feet.
Their sense of smell, touch, taste and hearing are all excellent. Rats can detect higher frequency than humans- hence the sound repellents on the market that are supposedly able to repel them. They run next to walls to assure them that no danger will come from that side. They use their whiskers and body hairs to feel out the path since they cannot see very well.
These rodents are very adept swimmers. It has been found that they can swim a half mile in open water, and tread water for 3 days! Commonly they swim through sewer lines to enter homes through the floor drains. Yet they can also climb sewer pipes up to the second floor for entry.
A mature rat can reach up and grab an object 18 inches off the ground. On top of that, these critters can jump 2 feet from a standing position, and 3 feet with a running start. Nearly made of rubber, rats have fallen from a 4 story building and appeared to be fine. They can squeeze through holes larger than ½” in Diameter.
As with all rodents, rats must gnaw on hard objects. Their incisor teeth grow nearly a half inch each month. That is about how fast our hair grows. Among other softer objects, rats can chew through lead pipes, plastic, cinder blocks, and wood.
Diet and Nesting Sites
Primarily they feed just after sunset, with a secondary feeding time in the early morning. In search of food they travel an area of about 100-150 feet in diameter. Consider that a rat foraging inside of a building may have a nest outdoors that is 100 feet away!
On average, adults require nearly an ounce of dry food and just over an ounce of water each day. They can go without food for 3 days. Yet only 1 or 2 days without water, before becoming ill. Protein-based foods are preferred, such as meat, fish, insects, nuts, and grain. Since they are quite adaptable, there isn’t much they don’t feed on. Household garbage and pet food are the most common food once inside. Not only is it easily accessible, it fits their dietary needs quite well.
Rats hoard food. Food is gathered and stored in hidden areas. This is important to consider when using rodenticides.
Although they can climb, they naturally are a burrowing animal. So they will nest underground level if practical. Normally burrows are shallow, approximately 8-18” underground. Also the burrows are under 3 feet short, with a central nest. Entry holes are 2-4 inches in diameter. Extra emergency exits are loosely covered with grass or dirt.
Some local neighborhoods have chronic rat problems. A mature colony of rats can develop an underground system that can extend an entire city block! Common nesting sites are found in burrows in ground cover, below slabs of sidewalks and foundations, and inside exterior wall voids, and sewers of coarse. When Norway rats inhabit buildings, they usually stay in the basement or on the ground floor. Additionally, rats prefer to nest close to a water source. It is important to note that rats often have a home nest and multiple secondary nests.
Indicators That Norway Rats Are Present
These sneaky critters can go a long time undetected. For example, if certain dogs are present, a rat will not poop out in the open. Their feces is usually the first thing people notice though. A single rat can produce up to 50 droppings per day. That can be hard for a rat to hide over time! Droppings are 3/4″ long and are the shape of a football. Fresh droppings are black and wet looking. You’ll find the highest number of droppings where they rest and feed.
Norway rats have an oily substance on their coats, called sebum. This is like a water-proof coating. Oil and dirt rub off along pathways and entry points. If you look closely you can find dark, stained areas where the rats travel. Runways can also be spotted, since they will be free from dust. Trails often have a tail drag between their tracks.
Sometimes you can hear them inside walls. It often comes across as shuffling or climbing. Scratching and gnawing noises are also common at night. If their are multiple rats nesting inside a wall you can hear squeaking and murmuring sounds. Once a customer thought there were baby raccoons in the wall. It can sound pretty similar to baby animals.
Once a rat has been around long enough, the area develops a very distinct odor. A sharp musky odor, mixed with the ammonia that their urine leaves behind; is the best way to describe it.