6.5.1 Types of rodent
Three types of rodent are commonly associated with public health problems.
Norway rats (Rattus norvegicus)
Also known as the brown rat or sewer rat, Norway rats are most numerous in urban areas. They burrow and live in the ground, and in woodpiles, debris, sewers and rubbish. Norway rats are omnivorous, which means they eat a wide variety of foods, but they mostly prefer cereal grains, meat, fish, nuts and some fruits. They do not travel more than 100 metres in search of water and food. When Norway rats invade buildings, they usually remain in the basement or ground floor. They reproduce rapidly (four to seven times a year producing eight to twelve young per litter with a gestation period of 22 days). The adult is relatively large in size, with a short tail and small ears. Their lifespan is 9–12 months.
Roof rats (Rattus rattus)
Also know as the black or grey rat, roof rats are more numerous in rural areas. They live in roofs, and eat mainly grains. They are smaller than Norway rats with longer tails and ears. They are excellent climbers and usually live and nest above ground in shrubs, trees and dense vegetation. In buildings, they are most often found in enclosed or elevated spaces in attics, walls, false ceilings, roofs and cabinets. They usually nest in buildings and have a range of 30–45 metres. They can often be seen at night running along overhead utility lines or fence tops, using their long tails for balance. The average number of litters a female roof rat has per year depends on many factors but generally is between three and five, with five to eight young in each litter.
Mice are smaller in size than rats and generally prefer cereals to eat. They are excellent climbers and can run up any rough vertical surface. They will run horizontally along wire cables or ropes and can jump up to 30 cm from the floor on to a flat surface. Mice can squeeze through openings slightly larger than 1 cm across. In a single year, a female may have five to ten litters of about five to six young. Young are born 19–21 days after mating, and they reach reproductive maturity in 6–10 weeks. The life span of a mouse is about 9–12 months.
6.5.2 Behaviour of rats