Norway rat (Rattus norvegicus): This rat is also known as the brown rat, common rat, house rat, barn rat, sewer rat, gray rat & wharf rat.
The Norway rat is an opportunistic omnivore, feeding on people’s foods and wastes or utilizing the natural foods that are available.
Some mature adults in established colonies may exhibit neophobic behavior and avoid traps, new bait containers and quite possibly new food sources that suddenly appear.
- Following mating a gestation period of approximately 22 days the female gives birth to an average litter of 8 to 9 pups however larger litters of 12 are common.
- The pup’s eyes are open at 9 – 14 days and are weaned 10 – 15 days later.
- Pups reach sexual maturity in8 – 12 weeks.
- Females may come into heat every 4 to 5 days and may mate within a day or two after a litter is born.
- In captivity a rat may live three or more years however wild rats have a considerably shorter lifespan with an average of 5 to 12 months. Most rats are killed by predators, other rats, people, or quite possibly die of disease or stress before a year old.
- The Norway rat is a fairly large rat with the average adult 16 inches in length from the nose to the tip of the tail and it weighs 12 – 16 oz.
- The Norway rat’s tail is shorter than the body. An identification technique used by many pest management professionals to determine between a Norway & Roof rat is to pull the tail over the body. The tail of the Norway rat does not reach beyond the ears while the Roof rats tail extends easily to the nose.
- The typical pelage color is grayish brown but can vary from pure gray to blackish to reddish brown therefore color should not be used as the sole method of identification.
- The Norway rat has relatively short ears and a blunt nose.
- The Norway rat is a ground dwelling mammal digging and constructing its nest within subterranean burrows. The impulse to begin digging a new burrow is triggered by the rat perceiving some protection. In part this comes from tactile feedback from the vibrissae. Rats often start new burrows beneath heavy or large rocks. Around buildings they may burrow under slabs or alongside foundations. Junk and objects lying on the ground may trigger digging of burrows as well. Norway rats may burrow anywhere however areas that offer protection (vegetation etc.) will be sought out.
- The burrow will be 2-3 inches in diameter with lengths varying between 1.5 – 6.5 feet with two or more additional bolt holes and a central den.
- Burrows rarely extend more than 18 inches below ground however rats may burrow 4 feet or more to get in and out of buildings.
- Peak foraging and feeding periods occur at dusk and again prior to dawn.
- If areas are quiet and undisturbed, it may be common to see rats foraging throughout the daytime, especially juvenile and subordinate individuals.
- Rats consume approximately 10% of their body weight daily.
- Norway rats commonly collect and carry off foods to either be stored in nests or hidden areas or to eat in a less disturbed and protected location.
- Subordinate rats may be forced to feed from leftovers or from less nutritious or even possibly vulnerable areas than that of the dominate animals.
- Norway rats require water on a daily basis.
- Stressed or hungry rats will also attack and cannibalize other rats.
Home range of an established Norway rat in urban areas is 25 – 100 feet from its nest. But the specific environment dictates the home range of most rodent families. Rats living close to easily accessible food tend to have shorter home ranges. Conversely, they will travel several hundred feet each night if necessary to acquire essential resources.
Radio telemetry studies have demonstrated rats liberated in areas foreign to them were recaptured 4 miles from the point of release. These types of studies explain how likely it is for the Norway rat to follow various urban pathways for considerable distances and establish new infestations in previously uninfested neighborhoods.