Mice and Rats

In addition to insect pests, commensal rodents such as mice and rats are a pest problem in both residences and commercial establishments throughout the Pacific Northwest.  Their urine and excrement can spread disease, and contamination to foodstuffs poses a serious health and economic threat to humans.

The house mouse (Mus musculus) is the most common rodent invader in buildings. Adults can range up to 3.5 inches in size plus the length of their tail, adding up to another four inches to its total length.  While they can gnaw their way into an open area through a wall or floor, they can squeeze through a hole as small as ¼ inch.  They will leave small (up to ¼ inch) fecal droppings wherever they travel.  They are excellent climbers and can easily access kitchen cabinet interiors or other locations to find food, preferring seeds or cereals for food.

The deer mouse (Peromyscus maniculatus) is slightly smaller than the house mouse and can be easily differentiated from the house mouse by their bi-color (gray and white) tail that is longer than half the length of the head and tail combined and covered with short hairs.  Primarily found in wooded or rural areas, the deer mouse has been identified as the primary carrier of hantavirus which can prove fatal in humans.

Norway rats (Rattus norvegicas) are the largest commensal rodents in the Northwest, with an average weight of about a pound and length (body plus tail) exceeding 13 inches. Their bodies tend to be shorter in length than their tail, and their nose is blunt in shape. They will leave behind droppings up to ¾ inch in size, up to three times the size of a house mouse.  In addition to gnawing their way through siding or other breaks in a building exterior, Norway rats have been known to gain entry into buildings through municipal sewer lines or via holes dug under shallow concrete foundations.  They prefer burrowing under concrete slabs, stream banks, or piles of rubbish.

Roof rats (Rattus rattus) are smaller than Norway rats, with tails longer than their bodies.  They are less common than Norway rats, with a range limited to the western parts of Oregon and Washington, especially near seaport cities.

Mice are curious creatures and will explore their surroundings. Rats, on the other hand, are shy by nature and will approach any new condition in their surroundings (such as new placement of a trap) with caution.  If a rat has a bad experience with something in its environment, such as getting sick from bait, it will shy away from the cause of the bad experience.  Both mice and rats are more active at night.

Corrective measures:  Keys to controlling commensal rodents include:

·         Identifying the pest (is it a mouse or a rat?).

·         Sanitation:  Not allowing anything to attract them, such as eliminating birdseed and other seeds that they can eat, sealing dry pet food containers, keeping food sealed in plastic or other rodent-resistant containers, etc.

·         Eliminating places to nest: To the extent possible, keep the environment in and around a structure free from areas where mice or rats may hide and nest.

·         Rodent proofing: Installing screening, flashing, and other mechanical guards to keep rodents out.

Complete control of rodent infestations generally requires professional assistance, especially where trapping and/or baiting may be necessary in addition to these other steps.  Leupitz Pest Control has had decades of experience using appropriate means to keep rodents out and eliminating existing rodent populations in structures.  Feel free to call us for additional help with these issues.