DTY Cockroach
Direct to you, a rousing rat review
Understanding the Norway rat’s taxonomy, biology and behaviors


Rats are nothing new, but read on for a rousing rat review. As both a reservoir and vector of numerous diseases, the rat is responsible for enormous loss of life, food and property. Even today, within both agriculture and urban centers, there is a constant battle between humans and rats. It is sometimes difficult to determine which side is winning.

The Norway rat (Rattus norvegicus) was the first species to be domesticated for scientific research and is also the most widely used animal in experimental studies of disease pathology, biological assay and nutritional and behavioral research. Ironically, public health can be hindered by the rats’ behavior, and at the same time, has progressed by the rats’ role in research.


  • Class: Mammalia.
  • Order: Rodentia.
  • Suborder: Myomorpha.
  • Family: Muridae (the largest family of mammals).


  • Average life span: 1.0-3.5 years.
  • Weight adult male: 267-500 grams.
  • Weight adult female: 225-325 grams.
  • Temperature: 99.9 degrees F (37.7 degrees C).
  • Respiration: 70-150 breaths per minute (bpm).
  • Pulse: 300-500 bpm.
  • Sexual maturity: 37-75 days, though females live longer.
  • Puberty occurs sooner in female rats.
  • Preferred environmental temperature: 50-68 degrees F (18-26 degrees C).
  • Preferred relative humidity: 40-70 percent.
  • Gestation litter: 21-23 days.
  • Litter size: 6-13 rodents.
  • Pup birth weight: 5-6 grams.
  • Weaning period: 21 days.
  • Water intake: 22-33 miliiters per day.

Possessing keen hearing, rats can sense high-frequency sounds. Additionally, smell and touch are extremely high functioning. As in all rodents, rats are nasal breathers. Visual sense is poor.

Behind the eyes are Harderian glands, which fill a large part of the ocular orbits. Interestingly, Harderian glands secrete lipids and a red porphyrin pigment, which fluoresces under UV light. Secretion increases with stress and/or disease.

Dental formula consists of incisor 1/1, canine 0/0, premolar 0/0 and molar 3/3. Generally, lower incisors are up to 3x longer than the upper incisors. Additionally, incisors are a yellow-orange color due to iron pigments. Incisors are open-rooted, but molars stop growing by around day 125.

The Norway rat is an omnivore, consuming almost anything. Nutrition should consist of at least 16 percent crude protein and 4-5 percent fat. Strictly seed-based diets tend promote obesity. Longevity is increased when rats favor a low fat, vegetable protein-based diet.

Although female rats are more likely to fight, rats are socially interactive animals. Mostly nocturnal, rats demonstrate cycles of activity during the day and night. When able to acclimate, adult rats tolerate cold well. Rats are proficient at gnawing, burrowing and climbing.

As an essential part of IPM, correct pest identification establishes the basis upon which all-successive pest management decisions are made. Poor identification means poor pest management!

The law classifies animals as “wild or ferae naturae” and “domestic or domitae naturae.” The former includes animals that are wild by nature, and, not having been subjected to confinement or control by man, live in a natural state.

Given the increasing liability of "getting the rat ID wrong,” it is important that the species is correctly identified through a "reasonable degree of industry standard of practice or standard of care."

In some cases, getting it wrong may get you sued! For you, an essential reason for a rousing rat review!

Stuart Mitchell, D.O., DVM, PsyD, BCE, is a board-certified family practitioner and entomologist, and a regular contributor to Pest Management Professional's Direct to You series.

PMP’s Direct To You provides pest management professionals with educational refreshers on timely and critical topics essential to operational success. This content is not be used as a substitute for obtaining legal advice from an attorney licensed to practice where you live. Look for the content-rich PMP Direct To You archives at mypmp.net/direct-to-you-archive.

This newsletter was produced by North Coast Media’s content marketing staff in collaboration with Bell Laboratories.

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