Rodent Biology and Habits

Rodents are one of the most numerous, successful, and adaptable of all living animal groups and differ from other kinds of animals by their front teeth which are specialized for gnawing. The teeth of rodents grow continuously throughout the animal’s life. Because of this fact, these animals have to gnaw frequently to keep the tips of their teeth worn down. There are over 3,000 different kinds of rodents in the world that range in size from small (fraction of an ounce) to large (more than 100 pounds) animals. Rodents of one kind of another occur in every kind of environment from deserts to tundra.

Rodents have a keen sense of smell and the animals produce many natural odors (pheromones) which attract others of their kind. Once rodents have entered a hole, room or building, their odors remain on the hole and attract many other rodents. Their scent is often left behind by grease marks made by the oils of the skin and by urine markings.

Rodents present in this country may either be native (New World) or exotic (Old World) animals. It is very important to be able to accurately identify rodents causing problems because these animals resemble each other but have quite different habits and living requirements. Native (naturally occurring) rodents include: mice (white-footed, pygmy, pocket, grasshopper, harvest, and jumping mice); rats (wood, cotton, kangaroo, and rice rats); voles; porcupines; pocket gophers; lemming; nutria; squirrels (ground, tree, and flying); chipmunks; marmots; prairie dogs; rabbits; muskrats; and beaver.

Exotic rodents (animals accidentally introduced into this country from other countries) are house mice and rats (Norway and black rats). Exotic rodents are easily identified by their scaled, nearly hairless tails (nicknamed "naked-tail rodents").

It is necessary for rodents to produce large numbers of young in order to survive. This is because they have a high rate of death. For example, house mice are able to reproduce all year when they are inside of a home or structure. During one year and under ideal conditions, a single pair of house mice is thought to produce over 3,000 offspring. Theoretically, this is possible because young house mice can reproduce when they are only 30 days old and females can become pregnant with a second litter while the first litter is still nursing. Native deer mice do not reproduce year round and produce fewer young. However, under ideal conditions, a pair of deer mice, theoretically are capable of producing a population of about 800 mice during their 4-month breeding period. They are an important food source to many other animals. Under natural conditions, the competition between mice for space and food and natural predation (fox and owls) removes 80 to 90 percent of all young mice soon after birth. When ample food, water, and shelter are available and predators are absent, mouse populations can blow up. Mice occupy as many spaces in homes and buildings as possible until a limitation of resources restricts the numbers of animals that can survive. Wood, brick, plaster, metal pipes, and cables are just some examples of the slightly rough surfaces that mice can climb. Their good balance allows them to run along horizontal electrical wires, ropes, and cables.

Native mice and exotic mice have much different behaviors. The exotic house mice have a small range of home space. They seldom travel more than 20ft from their nest to eat. The exotics are active all winter. They are very curious and will investigate many objects including traps. White-footed mice occupy a home range of about 1/3 to 4 acres and will travel 200 more feet from the nest to a feeding station. Expect to hear these mice in your homes after the sun sets for the evening.

Rodents can be responsible for spreading disease and rodents can damage (sometimes destroy) homes and their contents. These two reasons alone are the most important reasons for controlling rodent populations in and around your home.

Rodent Disease

Mice and rats are the most common destructive pests in homes and buildings. Old world house mice and rats (Old World house mice and rats) spread serious disease such as plague, typhus, rat bite fever, trichinosis, salmonella food poisoning and other infectious diseases.

Rodents naturally occurring in the country (native rats and mice) can carry plague; tularemia, leptospirosis (in urine), endemic relapsing fever, Rock Mountain spotted fever, and Q-fever. Sylvatic plaque is endemic in the western United States. In 1992, deer mice were identified as the most important transmitter of SIN NOMBRE VIRUS (Hantavirus Pulmonary Syndrome; HPS). Humans will become ill with Sin Nombre Virus after coming in contact with rodents, rodent feces, urine, or body fluids; or after inhaling dust arising from rodent feces or nesting materials.

Secondary health issues can arise when rodent food caches, nests, and dead rodent carcasses (poisoned animals or natural causes deaths) attract parasites, flies, carpet beetles, and other pests – all of which these creatures can become severe problems in homes and building structures.

Old world house mice and rats (Old World house mice and rats) spread serious disease such as plague, typhus, rat bite fever, trichinosis, salmonella food poisoning and other infectious diseases. Rodents naturally occurring in the country (native rats and mice) can carry plague; tularemia, leptospirosis (in urine), endemic relapsing fever, Rock Mountain spotted fever, and Q-fever. Sylvatic plaque is endemic in the western United States. In 1992, deer mice were identified as the most important transmitter of SIN NOMBRE VIRUS (Hantavirus Pulmonary Syndrome; HPS). Humans will become ill with Sin Nombre Virus after coming in contact with rodents, rodent feces, urine, or body fluids; or after inhaling dust arising from rodent feces or nesting materials.

The activities of rodents during the night time can result in human sleep disturbances and in rare cases, rodent invasions have been associated with paranoid fears and more serious accidents.

Rodent Destruction

Physical damage can be expected when rodents (and other wildlife animals) enter and infest buildings. The rodents often build nests and store large amounts of food (nuts, acorns, seeds, etc.) behind walls or in attics and this food harborage can cause structural damage and attract other pests as well. These animals can also burrow into or re-arrange attic and wall insulation. The rodent gnawing habit may damage upholstered furniture, collections, leather and paper goods, clothing, electrical lines and equipment including computers, security systems, satellites, etc.

Rodents burrowing near homes and buildings foundations from the outside can increase the rate of structural deterioration simply because this burrowing loosens the soil allowing for increased water penetration, and support excessive vegetation. Plus, the larger predatory animals are attracted to the mere presence of rodent burrows and they will enlarge the holds causing additional structural harm. Chances of home and building deterioration from weathering and moisture are greatly increase with rodent damage. Rodents often enter and make nests in parked machinery and vehicles; here they damage wiring and hoses. This can be quite serious should these vehicles be used for emergency response. Rodents frequently damage valuable ornamental plants and gardens as well.

Many structural fires each year in this country are thought to result from electrical wiring damaged by rodents!

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