Rats & Mice
The rodents that are of great concern in the urban pest control context, not just in Australia but in many countries, are:
- Norway rat (Rattus norvegicus)
- Roof rat (Rattus rattus)
- House mouse (Mus musculus)
These animals are well adapted to living in very close association with humans, sharing their food and shelter. Throughout history, rats and mice have been responsible for enormous losses of food and, owing to their ability to transmit diseases to humans by a variety of means, enormous losses of human life. Whether it be crops in the field or foods in store, rats still consume or contaminate vast amounts of food, and they can still pose a serious threat to health.Hence, it is not surprising that many countries have adopted legislation aimed at reducing levels of infestation. Urban pest control operators typically expend much energy in trying to control these very cunning and often cautious pests, which have so successfully exploited urban environments. ironically, laboratory-bred rats and mice have, in more recent years, played a very important role in medical research, pesticide evaluation and other studies, where animals akin to humans are used as a guide for implications regarding human health.
Biology & Habits
Before examining each of the pest rodents in closer detail, some of their general characteristics can be considered.
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 buildings 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 food source within reasonable range, the somewhat warmer nesting conditions may facilitate more productive breeding, Alternatively, rats may enter buildings owing to a change in the availability of food. Rats feeding in school premises, for example, may cause problems in adjacent buildings during school vacations.
Being basically social animals, rats and mice live in groups, in nests constructed of any soft materials available (eg paper, fabrics, insulation). Out of doors they may nest in burrows adjacent to waterways, under buildings and so on, in trees and vines, in garbage dumps, rubbish heaps and other places where food and shelter are within reasonable range. Indoors they may construct nests in wall voids, roof voids, under floors and even within stored foods.
Rats and mice are generally regarded as very adaptable, omnivorous scavengers. They are agile animals and mostly nocturnal, but they may range and fees during the day, particularly if the population is very large, food is short, or their is little disturbance or danger. In their movements to and from the nest site, they are very sensitive to and wary of, their environment. In their travels they tend to move and feed under or near cover, seldom running out into open spaces. this behaviour displays a marked reliance on the sense of touch and is much exploited in the placement of baits and traps.
When at rest, rats and mice often groom themselves, licking their fur and feet. Clearly, this behaviours is exploited when toxic powders are put down on surfaces from which rodents are likely to pick them up. As well, they constantly gnaw a variety of materials, but because their mouth and teeth are structured so that gnawings need not be ingested, this behaviours has little application in control procedures.
The senses of rats and mice are mostly very keen, with the exception of sight. in summary:
- Sight – poorly developed. They cannot images sharply.
- Smell – very keen. they use odour trails and can detect strange odours in foods.
- Taste – very keen. they can detect strange tastes and may associate ill-feeling with certain tastes and/or smells in food. This can cause ‘bait shyness’.
- Hearing – very keen. Their hearing range extends into the ultrasonic range
- Touch – very keen. As they are mostly nocturnal, with poor eyesight, there is much reliance on the sense of touch. Touch sensors consist mostly of nerve endings at the base of the whiskers (vibrissae) and of long guard hairs on the body – hence
Rats & Mice as Pests
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. At times, poultry may be killed and eaten by rats.
Gnawing: physical damage
The constant gnawing of rodents can be the cause of serious damage to a range of materials. Typically, they may damage doors, skirting, and other parts of the buildings, upholstery, books, food containers or packaging, and parts of equipment or machinery. The gnawing of wires and cables 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 matches collected in the nest.
Historically, the role that rats and mice have played in the transmission of diseases to humans has been of profound importance. the Black Death (bubonic plague), which claimed more than 25 million lives in fourteenth-century Europe, is perhaps the most documented case in history of rats and disease.
Rats and mice may transmit disease to humans by a variety of means:
- Contamination of food or utensils with rodent urine or faeces. Examples: Salmonella food poisoning (bacteria carried by mice or rats), choriomeningitis, mild meningitis (virus carried by mice), Weil’s disease, infectious jaundice (bacteria), tapeworm.
- Contamination by direct contact with urine or faeces, where bacteria seems to enter the skin through small scratches, for example, Weil’s disease.
- Indirect contamination via blood-sucking insects (ie ectoparasites such as fleas); for example bubonic plague (Black Death bacteria, via fleas).
- Indirect contamination via pets to humans; for example, favus, skin disease (fungus from mice to pets to humans).
- Contamination by directly biting humans; for example, rat-bite fever, relapsing fever (bacteria).
- Indirect contamination by being eaten by an intermediate carrier; for example, trichinosis (worm-infested rodent eaten by pig, worm-infested pig eaten by human).
Rats and Mice in Buildings pose a serious threat to human health. the disease threat alone is justifiable cause for concern and for the implementation of sound control procedures.