name applied
to various stout-bodied rodents , usually having a pointed muzzle, long
slender tail, and dexterous forepaws. It refers particularly to the
two species of house rat, Rattus norvegicus, the brown, or Norway, rat
and R. rattus, the black, roof, or Alexandrine, rat. Both species originated
in Asia, but have spread throughout the world, mostly on board ships.
The black rat was common in Europe in the Middle Ages and was responsible
for the spreading of plague. It has since been largely displaced in
cooler regions by the brown rat, which reached Europe early in the 18th
cent. and North America by 1775. The brown rat is the larger of the
two, growing up to 10 in. (25 cm) long excluding the naked, scaley tail
and sometimes weighing more than a pound (.5 kg). It is commonly brown
with whitish underparts and pink ears, feet, and tail. It is a poor
climber, but an excellent burrower and swimmer; it is found in the damp
basements and sewers of most temperate zone cities. The laboratory white
rat is an albino strain of the brown rat. The black rat is commonly
dark gray. It reaches a maximum length of 8 in. (20 cm) and has a longer
tail and larger ears than the brown rat. A good climber, the black rat
inhabits attics and upper floors in warm areas; it is the common rat
of the Mediterranean region, the SE United States, and Central and South
America. Rats are omnivorous, aggressive, intelligent, adaptable, and
extremely fecund. Females produce as many as 8 litters each year with
as many as 20 young per litter. The gestation period is three weeks,
and the young reach sexual maturity in about two months. Rats may live
as long as four years. They are social animals but sometimes fight among
themselves. Besides the house rats, the genus Rattus contains several
hundred wild-living species. In addition, many other members of several
different rodent families are called rats, e.g., the bandicoot rat ,
the wood rat, or pack rat , the rice rat, the muskrat , and the kangaroo
rat. House rats are classified in the phylum Chordata , subphylum Vertebrata,
class Mammalia, order Rodentia, family Muridae.
DAMAGE AND CONCERN
They live mostly
in and around human settlements, where they have few natural enemies
and an abundant source of food. They invade food supplies and cause
widespread destruction; they also spread human diseases such as typhus
and tularemia. Despite human efforts to exterminate rats, the house
rat population is probably equal to the human population.
Bibliography:
See H. Zinsser, Rats, Lice and History (1935); S. A. Barnett, The Rat,
a Study in Behavior (1963).
Columbia Encyclopedia,
Sixth Edition, Copyright (c) 2003.
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