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There are three species of commensal rodents that generally infest a structure. They are house mouse, roof rat, and Norway rat. We will look at the identifying characteristics or each and the recommended control methods or each. If there is a rodent in your structure that is not one of these three, then look go to Pestdude's PEST WILDLIFE page for further identification or just ask Pestdude! .
Contrary to the "Mickey Mouse" feeling of mice and rats, rodents are not animals that you want in your house or business.
They cause destruction that is almost unbelievable:
1. They attack our food in the fields, during processing, at the supermarkets, restaurants, and in our homes. What they do not actually eat, they contaminate. In fact, it is estimated that they destroy enough food each year to feed 200 million people.
2. Structurally, they damage doors, floors, ceilings, and walls as a result of their gnawing and nesting. They also gnaw at plumbing and wiring, resulting in floods, fires, and explosions, not to mention loss of production due to computer failures and power outages.
3. The health risks associated with commensal rodents are well documented. They have been responsible for, directly or indirectly, for such diseases as plague, murine typhus, Rickettsial pox, Salmonellosis, Rat-bite fever, and Weils disease or leptospirosis. Because of the habits of rats and mice such as traveling or dwelling in garbage bins, sewers, etc., they are a main cause of the spread of these and other diseases to humans.


Therefore, the presence of these rodents should not be taken lightly. They should be eliminated from the work place as well as the home. There are preventative steps that can be taken to keep these animals out.

1. Sanitation: This is one of the most important steps to be taken. The constant cleaning of restaurants and food handling establishments is, in some places, required by law in order to prevent infestation of rodents. Sanitation also includes proper solid waste management. Keeping garbage can lids on tight or dumpsters away from the structure will eliminate food sources in or near the structure. Leaking water pipes should also be fixed as soon as possible.
2. Exclusion: This means eliminating any openings that may allow rodents to enter the structure. With mice, this means any opening larger than 1/4 inch. With rats, this means any opening larger than 1/2 inch. To be on the safe side, all openings greater than 1/4 inch should be sealed or plugged up. Around doors and siding, expanding foam seems to work well. Around electrical or plumbing opening, steel wool or copper wool works real well. This also works well in areas where sealing with other material does not work because the rodents gnaw through it.

The use of baits and traps work very well with rats and mice. The placement and type of baits and traps depends on whether the rodent is a house mouse, roof rat, or Norway rat.



House mice has a small, slender body; approximately 3 -4 inches in length. The ears are large, the nose is pointed, the eyes are small and uniformly dark, the tail is semi-naked and is as long as the head and body together. The color is usually dark gray on the back and light gray on the belly, but color variations due occur. Their droppings are rod shaped, about 1/2 inch in length, and tend to be pinched at one or both ends. Mice can be differentiated from young rats by the smaller head and hind feet.
These rodents multiply quickly with a female producing 4 - 7 pups per litter and having a litter as quickly as every month. Their nests tend to be close to their food source, usually within 10 feet. These nests can be found in walls, closets, ceiling and cabinet voids, within large appliances, in storage boxes, bureau drawers, desks, or within the upholstery of furniture. Outdoors, these mice may nest in burrows underground. Nesting materials include anything that can be chewed and shredded.
Mice are very curious about their surrounding, especially new things. They also rarely travel in the open, but instead will follow along walls, boxes, ceiling joists, etc., or anything that prevents them from being exposed easily.
TREATMENT for house mice can be achieved with the use of mice bait boxes or mice snap traps, both are available at local hardware store. There does not seem to be a preference to either one except that snap traps will kill the mice immediately and disposal is easier. Baits, however, will get to a larger number of mice, but you have less control as to where they die.

The trick to using these items is to place them where the mice are going to run into them. Find their droppings, this will help to locate where they are. Place the bait / traps along probable runways. Placing them in the open rarely works. Also, place more than you might think you would need. Remember, mice are curious, so the more they can "check out", the more successful you will be. Mice are also territorial, so placing the bait / traps about every 10 = 15 feet apart will help to get more than one nesting area if they exist. Finally, again mice are curious. If your control success seems to decrease after a week or two, try moving the bait / traps a couple inches either way. This new placement will cause the mice to be curious again.


The Norway rat, also known as the house rat, brown rat, wharf rat, sewer rat, water rat or gray rat, has a stocky body approximately 6 -8 inches in length (but can grow much bigger) , a blunt nose, small ears, small eyes, and the tail is scaly, semi-naked and shorter than the head and body combined. The color ranges from reddish to grayish brown with buff-white underparts, but there are many color variations. The droppings are capsule-shaped, meaning that both ends are blunt and about 3/4 - 1 inch in length.
They breed in the spring and fall with the female producing 8 -12 pups per litter and may successfully wean 20 or more pups per year. Norway rats nest underground. This is usually done outside. On farms, they may nest in barns, granaries, silos, etc. In home, they may nest in dirt crawl spaces or under slabs with access through drains or holes. They will nest between 50 to 150 feet of each other and their food source. They are also neophobic, meaning they will shy away from anything that is new.
TREATMENT for Norway rats can take up to a month or more before success begins to be achieved. Placement of rat bait or rat snap traps should be along normal runways. Like mice, they do not like to run out into the open. However, because they are neophobic, they will stay away from the new baits and snap traps for a period of time. Be sure to read any bait packaging to be sure that the bait is not recommended to be replaced within a month. Stay away from meal type baits, they do not last as long. The pellet type baits work well. The larger the bait formulation, the longer the bait will last. When checking the bait for success, be careful not to move the station too much.


The roof rat, also known as the black rat, ship rat, gray-bellied rat, Alexandrine rat and white-bellied rat, is smaller and sleeker than the Norway rat. It is approximately 7 - 10 inches long, has a pointed nose, large ears that are naked, large prominent uniformly dark eyes. The color is usually grayish black to solid black, with the belly varying from buff-white to all gray. The droppings are spindle shaped and about 1/5 in length.
Their reproductive biology is very similar to the Norway rat with some differences. First, they are commonly found in the coastal areas of California, Oregon, and Washington as well as the Gulf and Atlantic coast states from Texas to Maryland, but have been known to frequently board ships in port.
The roof rat usually nests in the roof or attic areas of structures. They usually enter building near the roof by way of utility lines or vents. As the population grows, however, the roof rats will migrate to lower portions of the structure, eventually reaching the ground floor if necessary.
TREATMENT for roof rats is very similar to that of the Norway rat except that the concentration tends to be in the attic and upper areas of the structure. The placement and the time (due to the neophobic nature of rats) are basically the same.

If you have any questions, please ask Pestdude!

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