Rodents

Evidence of rodent activity exist beyond 50 million years.  They are believed to exist in all countries of our planet except Antarctica. The Norway rat occurs in urban or rural areas where it constructs burrows in stream banks and canals and adjacent to residences. The roof rat is a good climber and is frequently found living and nesting above ground level in trees or the upper stores of buildings. Because of the house mouse's ability to gain access to structures through small openings and to adapt to a wide variety of situations, it is much more common in buildings than either species of rat.

Rats consume a wide range of substances including garbage, meat, fish and cereals. The house mouse feeds primarily on vegetable material such as seeds, fleshy roots, leaves and stems. Occasionally, however, it will eat meat or insects.

Rodents destroy far more than they actually eat. According to the World Health Organisation, rodents cause a loss of 33 million tonnes of food annually – enough food to feed 200 million people.  Mice damage household articles by their gnawing activities, and they contaminate food. Besides damaging crops and grain reserves, rats often gnaw insulation from wires and have occasionally been known to cut through lead pipe and concrete dams. The tunneling activity of Norway rats causes structural damage to building foundations and platforms.

In the past century alone, more than 10 million people have died from rodent-borne diseases.  Although rodents are not major threats to our everyday health, it is justified to be concerned over the potential for rodents to transmit diseases. By their very nature and design, rodents make excellent “vehicles” for harbouring and rapidly transporting diseases.

Norway rats, roof rats, and house mice are the rodents most commonly found living in close association with man. They are called commensal rodents, referring to the fact that they live at man's expense without giving anything in return. Rats have very high reproductive rates. A pair of rats and their offspring could produce 1,500 more rats in only one year if they all survived.  Rats breed at 3 to 5 months of age, carry their young for 21 to 33 days and have 6 to 12 young per litter, and 4 to 7 litters per year. The actual figures within these ranges depend on the availability of food, the density of rats in an area and the age of the female rat. Although one female rat may produce up to 84 young in a year, on the average about 20 young per female per year survive to maturity. Female rats can breed again 1 to 2 days after giving birth. Breeding occurs all year; however, in most populations breeding peaks in the spring and autumn. Generally, rat populations are lowest in the winter and, on the whole, control will be most effective at this time.

Rats usually construct their nests near food and water. Nests are generally hidden in quiet, secluded places and are made of soft materials such as paper, cloth, feathers, grass, etc. They are bowl-shaped and approximately 20 cm in diameter. Newborn rats are completely helpless and are born naked with their eyes and ears closed. They develop rapidly, however, and by 9 to 14 days are covered with hair and beginning to explore their environment. They nurse until they are about 4 to 5 weeks old and by 3 to 5 months are independent and sexually mature. The average life span of a rat is one year.

Mice mature rapidly and by 1.5 to 2 months of age are old enough to reproduce. They carry their young for 19 to 21 days and have 5 or 6 young per litter and 5 to 8 litters per year. A female mouse can breed again 2 to 4 days after giving birth. House mice breed throughout the year and do not show any seasonal breeding peaks.

Mice build nests of soft materials such as grass, paper, or cloth in hidden secluded areas. Nests are usually 13 cm in diameter with a small entrance hole on the side. Mice are born naked with their eyes and ears closed. They develop rapidly, and in 2 weeks they are covered with hair, their eyes and ears are open and they are no longer totally helpless. In another week they begin exploring the nest area and eating solid foods. At 5 to 8 weeks of age the mice are independent and ready to breed. House mice live 1 to 2 years.

A female mouse can produce 40 young in one year; however, this rarely if ever happens. The actual number of births and young that survive to maturity depends on the availability and quality of food and the degree to which the mice are crowded.