The RatThe best-known rat species are the
Black Rat Rattus rattus and the
Brown Rat R. norvegicus. The group is generally known as the Old World rats or true rats, and originated in
Asia. Rats are bigger than most of their relatives, the Old World
mice, but seldom weigh over 500
grams (1
lb) in the wild. The common term "rat" is also used in the names of other small
mammals which are not true rats. Examples include the
North American pack rats, a number of species loosely called
kangaroo rats, and a number of others. Other rats such as the
Bandicoot rat Bandicota bengalensis are murine rodents related to the true rats, but are not members of the genus Rattus. The widely distributed and problematic commensal species of rats represent a minority in this diverse genus. Many species of rats are
island endemics and some have become endangered due to habitat loss or competition with
brown,
black, or
Polynesian rats.
In
Western countries, many people keep domesticated rats as
pets. These are of the species R. norvegicus, which originated in the grasslands of
China and spread to
Europe and eventually, in 1775, to the New World. Pet rats are Brown Rats descended from those bred for research, and are often called "
fancy rats", but they are still the same species as the common city "sewer" rat. Domesticated rats tend to be both more docile than their wild ancestors and more disease prone, presumably due to inbreeding.
The common species are opportunistic survivors and often live with and near
humans. The
Black Plague is traditionally believed to have been caused by the micro-organism
Yersinia pestis, carried by the rat flea
Xenopsylla cheopis which preyed on R. rattus living in European cities of the day; it is notable that these rats were victims of the plague themselves. It has recently been suggested that neither rats nor infected fleas would have spread fast enough through Europe to be a likely culprit, although this is controversial and research continues.[
citation needed] Regardless, rats are frequently blamed for damaging food supplies and other goods. Their reputation has carried into common parlance: in the
English language, "rat" is an insult and "to rat on someone" is to betray them by denouncing to the authorities a
crime or misdeed they committed. While modern wild rats can carry
Leptospirosis and some other "zoonotic" conditions (those which can be transferred across species, to humans, for example), these conditions are in fact rarely found.[
citation needed] Wild rats living in good environments are typically healthy and robust animals. Wild rats living in cities may suffer themselves from poor diet and internal
parasites and mites, but do not generally spread disease to humans.
Rats have a normal lifespan ranging from two to five years, though three years is typical.
Le pois, petit pois ou encore pois rond est une plante annuelle, de la famille des Légumineuses (Fabacées), largement cultivée pour ses graines, consommées comme légume, ou utilisées comme aliment du bétail. Les termes désignent aussi la graine elle-même, riche en protéines (25 %). Les pois frais sont plus couramment appelés « petits pois ».
