The three main domestic or commensal rodents found in Utah are the Norway rat, the house mouse, and the deer mouse. Domestic rodents are the chief vertebrate pests of humans because of their great reproductive capacity and their ability to adapt to new environments.
PHYSICAL CAPABILITIES OF RODENTS The Norway rat can: Gain entrance through any opening that is larger than 0.5 inch square. Crawl horizontally on any pipe or conduit. Climb both horizontal and vertical wires. Climb inside pipes that are 1.5 to 4 inches in diameter and outside of pipes up to 3 inches. Climb vines, shrubs, and trees or travel along telephone or power lines. Climb brick or other rough exterior walls that offer footholds. Jump vertically as much as 36 inches. Jump horizontally as much as 48 inches. Jump a gap of 8 feet and greater from an elevation of 15 feet. Drop 50 feet without being seriously injured. Burrow vertically in earth to a depth of 4 feet. Swim as far as 0.5 mile in open water, travel submerged in and in sewers. Gnaw through a wide variety of materials, including lead, adobe brick, cinder block, and aluminum sheeting.
The house mouse can: Gain entrance through openings slightly larger than 0.25 inch in diameter. Jump 12 inches horizontally.
HOUSE MICE BIOLOGY AND BEHAVIOR The most common household rodent is the house mouse. This mouse has large ears, a pointed muzzle, and a slender body. The tail is unicolored, has little hair, and is about as long as the head and body combined. Adults weight 0.5 to 0.75 ounce and the combined length of the head and body are 2.5 to 3.5 inches long. The tail measures between 3 and 4 inches long. The feces are rod shaped, 1/8 to 1/4 inch long. Although house mice are commonly found living in structures built by humans, they are also well adapted to living outdoors. They are common inhabitants of grassy fields and cultivated grain crops. Wild populations often move into buildings when weather becomes severe. The house mouse has poor vision and is colorblind. Mice have keen senses of smell, taste, hearing, and touch. They use their sense of smell to locate food items and recognize other individual mice. Mice use their long, sensitive whiskers on the nose and above the eyes as tactile sensors. The whiskers and guard hairs enable the mice to travel easily in the dark. House mice feed on a wide range of foods, although cereals seem preferred over other items. Most mice favor grains. Supplemental food items include foods high in fat and protein, such as lard, butter, nuts, and dried meats. The two main feeding periods of mice are at dusk and dawn. Because of their small size, mice must feed several times during a 24-hour period. This means that they are active day and night. Their range is normally 10 to 30 feet from the nest. Jump against a vertical surface and use it as a springboard to gain additional height. Jump from a height of 8 feet without injury. Run up almost any rough vertical surface, including weathered sheet metal and cables. Run horizontally along wires and small rope. Travel upside down along hardware mesh. Swim if it needs to, but do not dive below the surface, as do rats.
DEER MICE BIOLOGY AND BEHAVIOR The native deer or white-footed mouse occasionally invades buildings adjacent to fields or woodlands. Deer mice are about the same size or slightly larger than house mice. Deer mice can be differentiated from house mice by a distinct, bicolored tail with the upper portion brown gray and the lower portion white. Deer mice have small ears and eyes and a relatively short tail. The deer mouse is the most common host of the Hantavirus, but other small animals may carry the disease. Hantavirus is a viral illness that is transmitted from saliva, stool, or urine of infected animals. Once these waste products dry, the virus can become airborne. Infection usually results when the virus is inhaled. The illness is described as a severe respiratory illness that results in death for about 50 percent of its victims. Avoid activities involving exposure to mouse droppings. Domestic rodents contaminate food by defecation, destroy structures by gnawing, transmit diseases, and harbor parasites hazardous to humans and animals. Some of the diseases that rodents convey to humans are plague, murine typhus, infectious jaundice, food poisoning, ratbite fever, and rabies.
NORWAY RATS BIOLOGY AND BEHAVIOR The Norway rat is the common domestic rat in Utah. It has coarse hair, close set ears, and its muzzle is blunt. The tail is dark on the top and light on the underneath side. The tail is shorter than the combined length of the head and body. The fur is gray brown on the back and gray white on the belly. The adults weigh between 12 and 20 ounces and the combined length of the head and body is 7.5 to 10 inches long. The tail length is between 6 and 8.5 inches. The feces are capsule shaped and about 0.75 inch long. Norway rats can be found in warehouses, farm buildings, houses, sewers, rubbish, dumps, woodpiles, and building foundations. They are good climbers and they can jump 24 inches vertically. The Norway rat has poor vision but keen senses of smell, touch, taste, and hearing. Long whiskers on the snout serve the sense of touch. Their home range is often 100 to 200 feet. Norway rats and other domestic rodents are mainly nocturnal, but they may go about in undisturbed places during the day. They feed on virtually anything edible, are unable to vomit, and must drink water to survive.
DOMESTIC RODENT CONTROL METHODS Rodent control may involve the use of several control measures, including cleanup or sanitation, rodent proofing, and the use of toxicants and traps. Sanitation is important for rodent control. The elimination of shelter, food, and water is important. Keep grass, weeds, and other vegetation away from buildings. Piles of lumber, rocks, rubbish, and old equipment should be located away from buildings. Information specific to the control of domestic or commensal rodents in and around structures is covered in the Study Guide for Structural Pest Control.
Pre-baiting Mice and rats are cautious feeders and may reject new foods or eat only small amounts for the first several days. Conditioning rats to feed on a nontoxic version by pre-baiting can increase acceptance of toxic bait. If acceptance of pre-bait is poor, the bait should be changed. After a pre-bait is accepted the toxic bait should be used.
Bait Selection and Placement Anticoagulant baits are available in several types. Grain baits in a meal or pellet form are packaged in small plastic, cellophane, or paper packets. These packets keep baits fresh and make it easy to place baits into burrows, walls, or other locations. Rats and mice will readily gnaw into these bags to get at the bait. Anticoagulant baits that have been formulated into paraffin blocks are also available. These blocks are useful in sewers or where moisture may cause loose grain baits to spoil. Acceptance of the paraffin-block baits by rats and mice of is usually less than acceptance of loose grain baits. Sodium salts of anticoagulants are available water daily, they can be drawn to baited water stations. Although mice require little water to survive, water baits used where moisture is scarce can be an effective supplement to other control measures. The use of bait stations or boxes protects rodenticides from weather and provides a safeguard to people, pets, and other animals. Bait stations should have at least two openings and be large enough to accommodate several rats or mice at one time. Bait boxes should be placed where rats or mice are active. All bait boxes should be clearly labeled "Rat Bait" or "Mouse Bait," as the case may be. Pest control professionals should keep a written record of the locations of all bait stations so that another person can inspect and replace baits as needed. Records should be kept of activity indicating whether baits have been disturbed, if dead rodents were found, and the observation of droppings or tracks.
Rodenticide Safety Precautions All rodenticides present some degree of hazard to animals other than rodents. Persons who formulate rodent baits for their own use should use extreme care in handling the materials. Follow the label directions when handling rodenticide formulations. Wash thoroughly after preparing baits, using soap and water. Ready to use baits are safer to handle because they reduce risks involved in handling concentrated toxicants. The carcasses of poisoned rats and mice should be collected using tongs or rubber gloves. The bodies should be disposed by incineration or burial. In instances where there are only a few, they can be placed in a plastic bag and dispose of with other refuse. Remove and destroy all uneaten bait at the end of the poisoning period.
Traps Trapping can be an effective method of controlling rats and mice. Trapping is recommended where poisons seem inadvisable and it is the preferred method for areas where only a few rodents are present. Trapping has several advantages: 1. It does not rely on rodenticides. 2. The effectiveness can be observed. 3. Rodent carcasses can be removed, thus eliminating odor problems. Snap traps are generally more effective than cage traps. For rats, bait the traps with peanut butter, chocolate candy, dried fruit, or a small piece of bacon tied securely to the trigger. For mice, use bacon, nuts, hard sugar candy, gumdrops, or peanut butter. Leaving traps unset until the bait has been taken at least once reduces the chance of rats or mice becoming trap shy. Place the traps so that the rats and mice following their natural course of travel will pass directly over the trigger. Use enough traps to make the campaign short and decisive. Since mice seldom venture far from their shelter and food supply, traps should be placed from 3 to 10 feet apart in areas where mouse activity is noted. Place traps within 20 feet of each other for rats. Glue boards Glue boards are an alternative to traps. Glue boards catch and hold mice and rats that step on the surface. Like traps, glue boards need to be placed along the travel path of mice and rats. Glue boards should not be used where children, pets, or desirable wildlife can come in contact. Glue boards lose their effectiveness in dusty areas and temperature extremes may affect the tackiness of the adhesive.