Rats are one of the most destructive pests in the world: they spread disease, damage structures, contaminate food. In general, there are two types of rats in the lower mainland: Norway rats and Roof rats. Norwegian rats are usually grayish-brown. They are heavy and thick, 7 - 10 inches long, and they weigh between 10-17 ounces. Their tail is shorter than head and body, and the top is darker than the bottom. Their nose and muzzle are blunt. Droppings are 3/4 inch long, and are blunt at both ends.
Roof rats are usually black. They are slender, 6.5 - 8 inches long, and they weigh between 6 - 12 ounces. Their tail is longer than the head and body, and the top is the same colour as the bottom. Their nose and muzzle are pointed. Droppings are 1/2 inch long, and pointed at both ends. Rats can fit through openings that are as small as 1/2 inch in diameter; therefore, it is almost impossible to rat-proof a structure. Roof rats are very capable climbers and can therefore find entry points up on the roof. Norway rats burrow to a depth of four feet, and can therefore find entry points into crawl spaces and basements. Both types of rats are capable swimmers, and may travel through sewer lines and into homes. If you've never had a rat problem, you have been lucky! Because of rats' ability to enter through such small openings (as small as 1/2 inch diameter), they can gain access to almost any structure. Rats will typically search out a new home in late fall or early winter as the weather gets cooler and food becomes scarce. There are some measures you may take to make your home less inviting.

• Keep firewood away from your home. Firewood provides an excellent shelter from rain and cold.
• If you have a birdfeeder, allow birds to clean up birdseed that has fallen before adding more. Birdseed on the ground attracts rodents to your yard, and ultimately may attract them into your home.
• Keep dry goods (including pet food) in plastic containers. This is true for goods stored inside your house as well as in your garage. Rodents are very capable of chewing through paper and plastic bags, and once a food source is found, they will continue to come back.
• Keep garbage in tightly sealed containers.
• Keep clean! While good sanitation will not prevent a problem, poor sanitation may encourage a problem.
• Trim weeds, bushes, and densely growing plants like ivy and berry thickets. Keep branches from touching the roof or siding of house.

Rats are able to damage a number of goods in a number of different ways:

• They chew into stored food
• They gnaw anything softer than their teeth, and may do damage to electrical wires, wood, lead and aluminum sheeting, cinder block, sun-dried adobe brick, etc.
• They leave droppings.
• They may urinate anywhere they go.
• They produce a distinctive odor.

Not necessarily, but probably. It is possible that only one rat has gained access into your home; however, rats are in heat approximately every 4 - 5 days, and may begin a family anytime. Therefore, if you have one rat living in your home, there will likely be more within a month or so. Rats are in heat approximately every 4 to 5 days. After mating, gestation lasts between 21 to 23 days, and there may be anywhere from 5 to 12 pups per litter. These young rats will be able to reproduce when they are 3 months old.

Rats show aversion to new objects;( i.e. they don't like new objects in their territory, and it will take several days for them to accept a new object as part of their environment.) Garlough and Spencer (1944) note the word, mouse, can be traced to the Sanskrit word musha which is derived from a word "to steal." Mice were well known to the ancient Greeks and Romans and were featured prominently in their art and literature. This cosmopolitan rodent. is believed to have come originally from Cen- tral Asia. It is now found throughout the world from the tropics to the Arctic and Antarctic. House mice should not be confused with young rats. A young rat has a head and feet which look too large for the body. The mouse's head and feet are in proportion to its body. Adult house mice are about 3-1/2 inches/89 mm long. The ears are moderately large and distinct. Mice are dusty-gray, but some may be light brown to dark gray with the belly slightly lighter or a very light cream color. Their tail is semi- naked and about as long as the body and head combined (2-1/2 to 3-3/4 inches/65 to 90 mm). An adult mouse weighs 1/2 to 1 ounce/12 to 30 g. The albino form is bred and used for laboratory studies.

House mice can live outdoors as a field rodent. However, they should not be confused with pine mice, meadow mice, white-footed or dear mice, moles and shrews, all of which are entirely different animals. House mice are extremely prolific breeders. At 35 days of age they mature and carry embryos for 18 to 21 days. If a female aborts, she can become pregnant again within 48 hours. The average litter size is about six. Variations in genetics, food supply and temperatures can affect these numbers. At low temperatures, mice produce fewer offspring, and they are smaller in size. A female suckles her young for about four weeks. The female may become pregnant following parturition or while still lactating. In such cases, the gestation period will be lengthened. Therefore, if all goes well, a female can have litters approximately every 40 to 50 days. Under optimum conditions (often found indoors, mice can breed throughout the year. Outdoors, mice are more seasonal breeders, peaking in the spring and fall.

Newborn mice are extremely small, blind, pink and naked, except for short vibrissae. They weigh between 0.02 and 0.03 ounces/0.5 and 0.8 g. After two weeks, the eyes and ears open, and the young mouse is covered with fine hair. After about three weeks, the young mouse is fully covered with hair, makes short trips from the nest and begin.s feeding on solid food (Marsh and Howard, 1976). At four months of age an adult mouse weighs about 25 grams, slightly less than 1 ounce. Eaton and Cabell (19491, on studying laboratory mice, state: "Young mice may be moved from their dam at three weeks of age and the dam rebred. A female is not usually productive after 15 months, but may live much longer. Male mice have been known to live as long as 2-1/2 to three years."

Garlough and Spencer (1944!) note mice usually live for 15 to 18 months, and some have lived up to six years. However, considering their natural enemies,and the diseases to which they are susceptible, it is generally agreed their life expectancy is less than a year.

Women's liberation has a long way to go in the world of house mice. Each male mouse stakes out a territory and guards it. Within the territory can be several females and lower ranking males. While the dominant male is busy defending his territory, the female mice may be "getting acquainted" with lower ranking males. Female mice will often mate with more than one male. A mouse's territory depends upon a number of factors, including number of mice in the entire structure and arrangement of materials within the structure. The more mice present, the less territory each has. Some mice can remain in a desk or pallet for an entire lifetime, but it is important to keep in mind that the mouse is climbing up and down within the materials stored on the pallet or in the desk. Mice entering an already occupied territory are not welcome and are driven off. When mouse populations swell, the mice will seek out rodent bait stations, exposed window ledges and any other area where they can hide from other more aggressive mice.

Mice are cannibalistic and will feed on each other when hungry. Mice caught on glue boards may be partially eaten by other mice. Mice in multiple live traps will often be eaten by other mice caught in the same trap.

Because mice scurry from place to place and deposit fecal dropping~ wherever they please, the easiest way to determine if mice are present is to locate their drop- pings. Other signs include gnaw marks, small holes in walls and doors, and the pungent odor of their urine. The easiest way to discern active infestations is to sweep up the droppings and see if new ones appear the next day.

Emlen (1950) made a study of the distances mice travel by capturing 1,572 mice, marking them and then releasing them at the point where they were caught. He found the average distance was 12 feet/3.6 m and that 90 percent moved less than 30 feet/9.1 m and 70 percent less than 10 feet/3.0 m. From this he concludes mice are "stay-at-homes" and do not move around unless disturbed. As a result of his studies, Emlen recommends the distribution of a large number of poison baits spaced no more than 20 feet/6 m apart. Southern and Laurie (1946! note the average range of mice in cellars is not more than 48 square feetl4.5 sq m in 24 hours.

• Mice are excellent climbers and can run up almost any roughened wall without breaking stride.
• Mice, although preferring not to swim, can do so. More than once a live mouse flushed down a toilet has resurfaced a minute later.
• Mice can jump a vertical distance of 12 inches/30.5 cm from the floor onto an elevated flat surface.
• Mice are capable of jumping from a height of 8 feetl2.5 m to the floor without injury. .Mice can survive and thrive in cold storage facilities at 14° F/-10° C.
• Mice are capable of squeezing through an opening slightly larger than 1/4-inch/6 mm in diameter.
• Mice can run horizontally along pipes, wires and ropes.
• Mice develop thick long coats of hair when living in a cold environment (i.e., in cooler boxes).
• In six months, one pair of mice can eat about 4 pounds/1.8 kg of food and during that same period produce some 18,000 fecal droppings.
• Mice feeding on colored crayons will produce droppings based on the color of the crayon they feed on.

Mice chew on electrical wires and thereby are capable of starting fires.

Mice are not blind, but have poor vision and cannot clearly see beyond about 6 inches/15 cm. At 45 feet/ 15 cm they respond to outlines, not details (Hopkins, 1953) . Occasionally we hear of mouse plagues in which the mice become so numerous they overrun the country. These usually develop in the summer, following a mild winter and a plentiful food supply. Such plagues usually are terminated by a disease epidemic which quickly kills the mice; reducing them to normal numbers.

Hall (1927) observed such an outbreak in Kern County, Calif. The mice were for the most part fully grown. He computed the number of mice per acre at 82,280. He notes: "Truly the number of mice was almost unbelievable, and one who has not seen this or a similar outbreak can scarcely comprehended the vast numbers that can occur in a given area of limited extent. Certainly the numbers were to be reckoned in the tens, and possibly in the hundred of millions.'

The mice damaged grain, reduced sacks of straw to chaff, destroyed foodstuffs, clothing, bedding, linen and other articles in house.s, and gnawed holes through floors and walls of frame buildings. Hall arrives at the following conclusion in regard to this unusual outbreak: "...the causes of this overabundance of house mice may therefore be stated as: Favorable meteorological conditions, abundant food and shelter and removal of the principal natural enemies of small rodents that normally hold their numbersin check. The factor determining the time of the spectacular emigra- tion of the mice was, probably, the destruction of their food and shelter."

Hinton ( 1931) , in discussing the great mouse plagues of 1916 and 1917 in Australia, notes a farmer who baited for mice and picked up 28,000 dead on his veranda the following morning, and only stopped "because he was tired:' Besides feeding on grain, the mice ate such unusual articles as lead pencils, leaden bullets out of cartridges, and seaweed on the beach. A more recent consideration of management options during mouse plagues is provided by Redhead (1988).

Klimstra (1968) best describes the behavior of a mouse as its enters a structure in the following manner: "...he moves in this new territory for investigation and exploration, he tends to go along the edges. He will go a short distance and come back to where he made his entrance and then maybe he'll go a little farther and then, after a bit, a little farther. After a period of time he has investigated most of the edges of this facility. Now he has developed some confidence, but in addition, he has established patterns or blueprints which he is able to remember kinesthetically, that is, by subconscious recordings of muscular reactions which allow him to re- spond in various w~ys on the basis of what the past has been. Once he explores the edges, then he starts moving into the interior. The amount of time he is going to spend in this interior is going to depend on what's there. If you have various kinds of structures in this interior, he is going to start investigating and when he does, it's much the same as he did for the perimeter of the room. He is going to go into the interior areas at a given point and will explore around the edges of any structure. Again he is developing memory 'patterns and as he does so he may move. to another part of the interior. Pretty soon he will have several routes that he knows will take him back to his entrance place; he returns there because this is the place with which he has the greatest familiarity.

"We have to appreciate that when a mouse moves into a new environment he goes through a process of developing memory paths of use of this area, and this, of course, is an important principle which has to be considered in any program of control. If you are dealing with a new mouse coming into a building, you know that he is going to be around the edge, but after he has been there for a while (which may take no more than about an hour) he may learn other patterns of movement. As I say, the diversity of the interior of this area is going to determine a great deal how simple it's going to be to be able to trap him or bait him. But, if something happens to his home base, that point where he came in, he suddenly becomes all excited and starts scurrying around because that is the one thing with which he had greatest familiarity. In about 15 to 20 or 30 minutes, he will have established some other place as a home base. It may be one of those items that is in the interior of the room.

"Another thing that we see in conjunction with house mice is that if you make changes in this area, if you move any of the facilities, immediately it activates the mice. This is important to them because they operate in the fashion that they do, that is, on the basis of the subconscious recording of patterns 0( muscular movement. They have to find their way around and become totally familiar with it again or otherwise if they are running after being frightened or scared and trying to return to their home base, they won't know where these obstacles are and may run into them. You must remember that mice are relatively nearsighted, Also, even though they may be able to establish scent trails, when they are moving fast, they don't have time to pick up these trails. The end result is that they do not have a familiarity as to where these objects are, which will cause them to certainly run into them.

In a stored food area the food is stacked on skids and there is some readjustment of these stacks, this is how you bring these mice out of their confined areas; they are now subject to trapping because they are out to investigate the rearrangement:

In the process of moving about the environment, the mouse urine marks the pathways. Odors associated with this marking are distinctive and will distinguish resident from foreign mice. A male's urine will be different from a female's. Thus, in any mouse colony a complex olfactory communications network exists (Hurst, 1989).