Pest Library - Rats

RatThe most well-known rat species are the Black Rat Rattus rattus and the Brown Rat Rattus 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 in the wild. The common term rat is also used in the names of other small mammals which are not true rats.


Food & Habitat

The Brown Rat is a true omnivore and will consume almost anything, but with cereals forming a substantial part of the diet. They are usually active at night and are good swimmers, both on the surface and underwater, but (unlike the related Black Rat Rattus rattus) are poor climbers. They dig well, and often excavate extensive burrow systems.



The Brown Rat can breed throughout the year if conditions are suitable, a female producing up to five litters a year. The gestation period is only 21-23 days and litters can number up to fourteen, although seven is common. The maximum life span is up to three years, although most barely manage one—a mortality rate of 95% is estimated: predators, intraspecific conflict are major causes. Brown Rats live in large hierarchical groups, either in burrows or subsurface places such as sewers and cellars. When food is in short supply, the rats lower in social order are the first to die. If a large fraction of a rat population is exterminated, the remaining rats will increase their reproductive rate, and quickly restore the old population level.


Rats live wherever people live. It is often said that there are as many rats in cities as people, but this varies from area to area depending on climate, etc. Brown Rats in cities tend not to wander extensively, often staying within 20 meters (65 ft) of their nest if a suitable concentrated food supply is available, but they will range more widely where food availability is lower.


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