The black rat (Rattus rattus) (alt. ship rat, roof rat, house rat, Alexandrine rat, old English rat) is a common long-tailed rodent of the genus Rattus (rats) in the subfamily Murinae (murine rodents). The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 6th century AD and spreading with Europeans across the world. Today it is again largely confined to warmer areas, having been supplanted by the brown rat (Rattus norvegicus) in cooler regions.
Despite its name, the black rat exhibits several colour forms. It is usually black to light brown in colour with a lighter underside. In the 1920s in England, several colour variations were bred and shown alongside domesticated brown rats. This included an unusual green tinted variety. Today, very few people today keep black rats as pets. Most pet rats (or fancy rats) are domesticated brown rats.
A typical black rat will be 15–20 cm (5.9–7.9 in) long with a further 20 cm (7.9 in) of tail. It is nocturnal and omnivorous, with a preference for grains and fruit. Compared to the brown rat, it is a poor swimmer, but more agile and a better climber, tending even to flee upwards. In a suitable environment it will breed throughout the year, with a female producing three to six litters of up to ten young. Females may regulate their production of offspring during times when food is scarce, throwing as few as only one litter a year. R. rattus lives for about 2–3 years. Social groups of up to sixty can be formed.
Rats have litters of 6to 12 young, which are born 21-23 days after mating. Young rats reach reproductive maturity in about three months. Breeding is most active in the spring and fall. The average female rat has 4-6 litters per year.
The above information is from Wikipedia The Free Encyclopedia.