d. The best single way to distinguish rodents from other mammals is by the
location and shape of their teeth. Conspicuous are the strong, well-developed front
teeth, or incisors. There is a single pair of these prominent incisors in both the upper
and lower jaws. The incisors are separated from the molars by a decided gap. In North
America, the only similar tooth arrangement is found in the rabbits, hares, and pikes.
These species have two extra incisors behind the front pair in the upper jaw. Because
of these extra incisors, they are placed in a different order of mammals, the
e. The three domestic (taken from Family Muridae) rodents may be
distinguished from our native rodents by the character of their tails. The tails of
domestic rodents generally are more naked and scaly than those of the native rodents.
a. Norway Rat (Brown, Sewer, Wharf, House, or Barn Rat) Rattus
(1) This is the most common and the largest domestic rat in the US. Full-
grown specimens usually weigh between 10 and 17 ounces (280 to 480 grams). The
coloring varies from reddish brown to black on the back and sides. The belly is grayish
or yellow white. The body is thicker, and the head blunter, than in the related roof rat.
The muzzle is blunt, and the ears are small and densely covered with short, fine hair.
The female has 12 mammae (teats). The tail is shorter than the combined head and
body length and is distinctly light in color on the underside. The range of travel for this
rat is 100 to 150 feet. Norway rats reach sexual maturity when they are 2 to 3 months
old. A female rat may raise from four to seven litters a year, with an average of eight to
12 young per litter. A life span of about 1 year is the same for all three domestic
(2) The Norway rat is distributed throughout the world. It is somewhat less
agile than other species and prefers to burrow for nesting. It is only a fair climber and
so usually confines its activities to the lower parts of buildings. It is an expert swimmer
and often occurs in great numbers along the banks of canals and other waterways. At
times it may live in the fields, particularly in the vicinity of dumps and similar food
sources. Normally, however, it occurs in or near buildings, where it prefers narrow