Meet the commensal rodents of California

Oct 8, 2021, 14:45 PM by Fred Speer

Rodents are fascinating creatures. They are far more intelligent and clever than we humans give them credit, and they are a worthy adversary for any pest management professional.

Clark, your friendly pest control, termite, and grounds care expert, has a great deal of experience dueling with mice and rats. Allow us to introduce you to the commensal rodents of California. (The term commensal, when used to describe rodents, refers to those species that live among humans and are dependent upon us for food and harborage, as opposed to such non-commensal outdoor species as pocket gophers, ground squirrels, and meadow voles.)

The house mouse

The adult house mouse ranges from 2 1/2 to 3 3/4 inches in combined length of head and body, with 2 3/4 inches added in tail length. Its fur is short and its color is gray, with either light gray- or cream-colored fur under its belly.

Mice are found where food and shelter are plentiful, and if you’re seeing mice active in the daytime, you may have an exploding mouse population. Mice can pump out eight litters, with five to eight pups per litter.

Mice prefer nesting sites that are dark, in secluded places with an abundance of nesting materials, which can include paper products, cotton, packing materials, insulation, and fabrics. They typically will eat anything, but they prefer seeds and insects.

A mouse will investigate and explore to see if anything is new or different, and it will establish new travel routes if necessary. Territories vary in size, but they typically are small. Mice can gain access through openings larger than 1/4 inch, which allow them many points of entry. Their droppings are typically 1/8 to 1/4 long, rod-like, and smooth, with pointed ends.

Mice can be vectors and may carry pathogens for or contribute to the following diseases and infections: hantavirus pulmonary syndrome, salmonellosis, lymphocytic choriomeningitis, leptospirosis, rat-bite fever, ringworm, dermatitis, bubonic plague, murine typhus, and rickettsialpox.

The Norway rat

The adult Norway rat is about 16 inches long, with a combined head and body length of nine inches and tail length of seven inches. Its body is stocky and muscular, built for digging and burrowing. Its fur is coarse and shaggy, and its color is usually brown with scattered black hairs.

Norway rats are known to damage and destroy material by gnawing. They will eat and contaminate stored food. The Norway rat is nocturnal, and, unlike the house mouse, it will avoid new objects introduced into its territory. It prefers to nest in the lower parts of structures – in basements, in piles of debris and stored things, or in merchandise – but also been found outdoors on or around riverbanks, railroad embankments, piles of rubbish, and under concrete slabs. The Norway rat will eat anything, although it prefers high-protein items like meat, fish, and cereal grains.

The roof rat

The adult roof rat is about 14 inches long, with a body length of six inches and a tail length of eight inches. Its fur is soft, and its color can be sooty black on the back and gray underneath. Its body is sleeker than that of the Norway rat.

The roof rat is also known to damage and destroy material by gnawing. It eats and contaminates stored food, is nocturnal, and will shun new objects introduced into its territory. Its nesting preference is for the upper parts of structures, but it also has been found in crawlspaces as well as outdoors in trees.

Once the roof rat has established a harborage, it tends to follow the same route to its food and/or water source, keeping its path clear of debris. A roof rat will feed on anything, but it prefers seeds, nuts, fruit, and berries when in season. It also may feed on snails, slugs, and insects.

If you suspect your home is being threatened by rodents, call California’s trusted rodent expert, Clark, at (800) WE-NEED-YOU (936-3339) or email us at

Clark Pest Control is committed to safeguarding your home from pests during these challenging times. Our service technicians use such personal protective equipment as gloves, masks, and respirators, they practice social distancing, they call ahead to notify before a service, and they adhere strictly to all Centers for Disease Control and Prevention guidelines when servicing inside or outside your home.

Until next time, the pest management professionals at Clark Pest Control thank you for helping to keep unwanted pests out of your home.

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