There are approximately 32 species of rats, mice and voles in California. Only a few of them are pests. The deer mouse (Peromyscus spp.) is one of the most common rodent species found throughout most of the United States. They are 4" - 9" long, are reddish-brown in color with a white chest, white feet, and a bi-colored tail: brown on top and white on bottom. Their natural habitat is in rural and semi-rural areas, where they inhabit fields, pastures, and various types of vegetation found around homes and outbuildings. This mouse commonly invades garages, attics, sheds, wood piles, crawl spaces, as well as general living quarters of homes. Deer mice can carry Hantavirus which can be very serious in sheds or rooms with no air circulation.
Mice can enter 1/4" openings - or they can be carried inside. They may get in through broken windows, poorly screened attic and foundation vents, openings through any walls created by cable, oil, propane, electric, gas, water and/or sewage services, and through any other openings or cracks or crevices in foundations, walls or roofs. They can also chew holes directly through siding and/or window or door frames.
While house mice (Mus musculus) aren’t linked to Hantavirus, they are very prolific and very unpleasant to have infesting your home. Under optimum conditions, house mice breed year round. Out-of doors, house mice may tend toward seasonal breeding, peaking in the spring and fall. Females may produce as many as ten litters (about 50 young) in a year. At very high densities, however, reproduction may nearly cease despite the presence of excess food and cover.
Although mice primarily are active at night, some day activity occurs. Movements of house mice are largely determined by temperature, food, and hiding places.
House mice prefer cereals over other items, although they will feed on a wide variety of foods. Mice sometimes search for foods high in fat and protein, such as lard, butter, nuts, bacon, and meat. Sweets, including chocolate, are taken at times. Mice get much of their water from moisture in their food, but they will drink if water is readily available. Mice in buildings catch and eat flies, spiders, centipedes, cockroaches, beetles, millipedes and other arthropods. Outdoors house mice consume a wide variety of weed seeds, grass seeds, various grains and vegetation. In addition they consume many insects and other invertebrates, e.g., slugs, spiders and centipedes.
Norway rats (Rattus norvegicus) and roof rats (Rattus rattus) are common pests. They are much larger than mice. Roof rats frequently get into homes and will get into attics and walls, will Norway rats prefer to burrow outside.
Rodents can easily co-exist with humans, living in their walls and attics and sharing their food and water. They love pet food, stored bird seed, fruits that may left out on counter tops or anything else in the pantry. They are skilled at hiding in the structure during the day then finding ways to enter the living space at night to gather food. They often have passage ways such as holes in walls behind appliances, beneath kitchen cabinets or inside closets that provides them access without being recognized by the homeowner. They constantly mark their pathways with urine or pheromones as a way to navigate back and forth. Once they find a safe place in a structure, they live and breed there, having several litters a year.
Besides the physical damage they're capable of – like gnawing on doors, carpet, baseboards, furniture, sheetrock, siding, roof shingles, electrical wires, a/c ducting, appliance water lines, etc. – they also pose a health risk from their urine and droppings that are left behind on pantry shelves, food, food containers, counter tops, and areas where they are nesting.
Rodents can harbor a number of pathogens in their urine and fecal material that can be transmitted to both humans and pets. Worldwide, rats and mice are known to spread over 35 diseases. Rodent-borne diseases can be spread to humans through bite wounds, consuming food or water that has been contaminated with rodent feces, coming in contact with surface water contaminated with rodent urine, or even through breathing in germs that may be present in rodent urine or droppings that have been stirred into the air by someone moving through an attic or a crawl space (a process known as "aerosolization").
Never use rodenticides when controlling rodents as they often carry parasites such as fleas that will leave a dead animal and bite pets or people, and some fleas are vectors of plague.
Hantavirus Pulmonary Syndrome is a rodent-borne virus that is spread through the inhalation of rodent urine or fecal particles.
Lymphocytic choriomeningitis (LCM) is a viral disease that people can get by either inhaling infectious airborne particles of rodent urine, feces, or saliva, or by ingesting food contaminated with the virus.
Rat-bite fever is a bacterial illness that can be transmitted through the bite or a scratch by a rodent or by ingesting food or water contaminated with rodent feces.
Leptospirosis is a bacteria that is transmitted by eating food or drinking water contaminated with urine from infected animals.