The distribution and abundance of pest rodents are largely determined by the availability of food and shelter. Rats and mice may live and nest within buildings indefinitely, provided they have access to food (perhaps water) and shelter. Often, rodents will enter and nest in building only seasonally. In such cases, the rodents may begin to investigate buildings in autumn or winter, for if a suitable nesting site is established with a food source within reasonable range, the somewhat warmer nesting conditions may facilitate more productive breeding. Being basically social animals, rats and mice live in groups, in nests constructed of any soft materials available (eg: paper, fabrics, insulation). Indoors they may construct nests in wall voids, in roof voids, under floors and even in stored foods.
The presence of rats and mice in buildings is usually regarded as undesirable from the viewpoint of food spoilage and contamination, physical damage, and the transmission of diseases to humans. 
Eating and contamination of stored foods.
Rats and mice are responsible for enormous losses of food in store, either by directly eating the foods or by rendering them inedible through contamination. As the rodents move in and around stored foods, they contaminate the food with droppings (of which often more than 50 per day are produced), urine (which tends to be sprinkled on surfaces over which they travel) and hairs.
Gnawing: Physical Damage
The constant gnawing of rodents can be the cause of serious damage to doors, skirtings and other parts of buildings, upholstery, books, food containers or packaging, and parts of equipment or machinery. The gnawing of wires has caused the breakdown of telephone systems and short-circuiting, which may result in equipment breakdown or, at worst, very costly fires. Fire damage has also resulted from the gnawing of matches collected in the nest.
Disease Transmission
Among the many diseases transmitted to humans by rodents, perhaps the most insidious and widespread problem involves the distribution of food poisoning organisms (eg: Salmonella bacteria). Unfortunately, the nature of disease organisms of this type is such that it will always be difficult to pinpoint, without any doubt, the cause of disease transmission. It is very likely that rats and mice play a significant role in the transmission of such diseases, particularly those which are gastro-intestinal and somewhat difficult to track. |
