Rodents

Mice

Origin: This species originated in Eastern Asia in arid grasslands, allowing it to evolve the ability to survive without needing frequent water. It now occurs throughout the world.

Biology: A prolific breeder, the House Mouse is sexually mature at 2 months old, has a gestation period of only 3 weeks, and averages 5 to 8 young per litter, but potentially up to 15. Each female may give birth to 8 litters. The life span can be from 2 to 3 years. The House Mouse is a nibbler, consuming small quantities of food at many feedings. They are “curious”, and tend to investigate new objects that are placed in their environment. Favored foods may be grains, dried fruits, nuts, and sweet materials. They are known reservoirs of diseases such as rickettsial pox (mites), typhus (fleas), and filth problems with Salmonella, tapeworm, roundworm, and others parasites. 

Identification: Adults remain small, less than 7 inches long from tip of nose to tip of tail. They have hairless, scaly tails that separate them from meadow or deer mice, and ears relatively bare of hairs. A young rat looks similar to the House Mouse, but the rat has feet and eyes that are disproportionately large in comparison with its head and body. 

Mice

Rats

Origin: Evolved in Central Asia, but reached Europe in the 1700’s, the United States later that century, and now it is found throughout the world. It is a rodent of cooler climates, but now also infests many tropical environments as well, primarily in the seaport areas.

Biology: This rat is commonly sold as a “pet rat”, and has been bred for white coloration as “lab rats” as well, leading to the occurrence of white and brown marked races. It is primarily a ground dweller, although it can climb very well, and prefers to reside in burrows. It swims very well and often lives in sewers and other underground water systems. It is primarily a nocturnal animal, and will restrict its range of movement only to that which is needed to find food and water, perhaps only 20 or 30 from home. Norway Rats are omnivores and opportunistic feeders, feeding on any natural or human foods available. They are neophobic and may avoid new objects placed in their environment for some time. A normal life expectancy for them is one year or less, although when cared for they may live several years. The gestation period of the female is 22 days, litters average 8 to 9 pups, and she may have several litters in her one year. Damage from gnawing can be extensive, as they chew on pipes of plastic or metal, wires, wood, or furnishings and walls, and commonly bite humans. While not the primary reservoir of bubonic plague, they have the potential to spread this disease, along with several others as well as filth infections. 

Identification: Adult rats are large and robust, being up to 16 inches from nose to tip of tail. Their tail length is shorter than their body length, and it is scaly and almost without hairs. Colors range from white to brown to mottled, or blackish gray, reddish brown, and other variations. In relation to its head it has a blunt nose, small eyes, and small ears. 

Rats

Voles

Origin: At least 84 species in this genus, with Microtus pennsylvanicus most prevalent east of the Rocky Mountains and north into central Alaska, and M. californicus most common in the western states. These are native animals.

Biology: Favored foods are fresh foliage and flowers in the warm months, seeds and grains in cold months, or even the bark of young plants and trees in the winter. Voles may be very destructive to grain and vegetable crops. Nesting is done is burrows in shallow soil or in thick grass and vegetation, and distinct runways are created above ground as the mice travel and forage. Breeding can be done year round, with the highest activity from March until November, and mating takes place immediately following the birth of a litter. There is an average of around 6 young per litter, and the potential exists for a breeding pair beginning in the spring to result in almost 3000 mice by the fall. There can be up to 10 litters per year, and population explosions result about every 4 years. 

Voles