Hunting House Mice in Office Buildings


December 23, 2015

Mice are so small, they can squeeze through a hole the size of a dime.  Photo: © Brey

Mice are so small, they can squeeze through a hole the size of a dime.
Photo: © Brey

You should already know these facts about the house mouse (Mus musculus), but they’re worth reviewing.
⦁ are so small, they can squeeze through a hole the size of a dime;
⦁ tend to be nocturnal;
⦁ often hide in inaccessible areas;
⦁ can spread quickly through a structure via elevators and packages; and
⦁ multiply rapidly, and if you cannot find all the mice, the few remaining will rebound in months.

Fellow PMP Hall of Famer Dr. Bobby Corrigan (Class of 2008) reminds us mice are attracted to three areas: shadow, warmth and lines. With these challenges, how do you scientifically determine where and how to find mice? By developing a system that works.
My system includes these critical steps:

  1. Talk to the building’s key occupants. Find out where they’re seeing and hearing mice or finding mouse droppings. Record every instance of a sighting and who was involved. Continue to keep records of sightings throughout the time it takes to eliminate the mice.
  2. Inspect the exterior and flat rooftop for conducive conditions and signs of infestation. Find out what rodent control program is in place, outside and inside the structure. Look for, and make note of, areas that need rodent proofing. In colder climates, install multiple traps on the roof, but bring them inside when it begins to snow. In warm areas, leave the traps out all year. Inspect and record areas where underground wires, piping and ducts enter the building. Find out whether any construction is planned on the exterior of the structure.
  3. Inspect critical areas inside the structure. In situations where ports are inaccessible, request the client create some sort of access.

These are the critical areas you should inspect inside a structure:

  • All food areas, including vending machines, coffee areas and kitchens. A cafeteria kitchen might require as much as a full day for the inspection and installation of rodent control devices. Include suspended ceilings and recyclable bins in your inspection.
  • Restrooms. Examine pipes and wall voids. They’re not typically a significant area for infestation, but a good inspector goes above and beyond.
  • Pipe chases. A pipe chase, which hides the plumbing system behind a wall, can run from the roof to the basement of some buildings. Fortunately, most have access ports. If you encounter one that doesn’t, create access to critical pipe chases to make them more accessible.
  • Lobby/atrium. Mice in nature live in soil. Inside a structure, this can translate to harborage in potted plants found in places such as lobbies or atriums.
  • On-site daycare center. A number of companies provide daycare services for the children of employees. These centers serve food to children and provide (lipid-containing) crayons for coloring. Mice thrive on both. The voids below the storage cabinets also serve as excellent mouse harborages.
  • Mailroom. From this area, packages are transported on wagons throughout the entire building. Keep in mind some environmentally friendly packing materials are produced using rice hulls, which can serve as food for cockroaches and mice.
  • Stockroom. What is the inventory flow pattern of products such as toilet paper, florescent bulbs and water-cooler bottles? They can become highways carrying mice. Pinpoint where they’re stored after entering a building.
  • Custodial closets. Closets where custodians and housekeepers store their cleaning products, tools and equipment are often locked and rarely cleaned. I put at least one glue board on each shelf and two at floor level in corners.
  • Maintenance shops. On-site shops often set their own rules and include a refrigerator, hot plate and sink area. Sometimes they’re hidden in a small sub-basement area. Find and inspect them.
  • Mechanical equipment room. They’re always warm, dark and rarely examined.
  • Telephone room. This is not an easy area to access because the telephone company, not building management, typically maintains the keys. Plan ahead to get in, and be sure you’re on time for the appointment. You might only be able to gain access to this room twice a year, so always schedule an inspection in advance.
  • Information technology (IT) room. Computer rooms can be complex and are sometimes built on a raised floor. It is essential to inspect the void below the floor, particularly the corners. Special suction cups are used to lift the floor tiles. Find out where these suction cups are stored. Remember that under that floor is a maze of wires, which are ideal for mice to chew. Crashing a server is a fast track to being fired from an account. Also, make sure employees know that keeping live plants and eating food in this area should be forbidden. Finally, never use rodenticide in this room because baits could attract insects, and dusts can damage computer equipment.
  • Loading dock. This is a main artery used to bring products into a building. Because it’s open to the exterior and the area where trash is stored often, the loading dock is attractive to rodents. Keep in mind house mice start from a building’s exterior. Materials stored against walls and long-term storage of paper are commonplace here. Help make sure these materials are rotated. In rural areas when nearby fields are cut, thousands of mice can invade through a dock’s door in one night. In inner cities, garbage trucks and other vehicles transport mice daily.
  • Trash area. This constitutes the final Dumpster and each trash can, and the flow pattern in-between. Learn the pattern and speak with the building’s trash collectors to be sure they report any rodent activity.
  • Crawl areas. These can be finished spaces or dirt lines. They can be a few feet high or less—even so, you must get in there and look. Have a jumpsuit available so you can take it off when emerging without looking like a mess.
  • The unknown. You never know what you’re going to run into, but keep looking.


Cubicles are critical, too

Remember, a mouse can live its entire life inside a desk. When mice are reported, you must check every desk drawer. The wires running to desktop computers are often in encasements that run along the floor and wall partitions. Mice can use these as runways and chew on the wires.
Radiators around a room’s perimeter run the piping system through walls and are essentially mouse highways. Sometimes glue boards dry out when placed under radiators, making it essential to rodent-proof before doing anything else.

Taking care of business

Request the appropriate ladders and keys are provided before your inspection. If you find you need something during an inspection, make arrangements to get these items, but continue by inspecting nearby areas. Also, learn the names of at least three people involved in the building’s management who were responsible for hiring you in the first place. If you come back to find the one person responsible for hiring you is gone, and you’re not protected contractually, you may be gone, too.

Last, but not least

The amount of time and frequency required to inspect each area will depend on the presence or absence of mice, the sanitation level and history of each area, as well as any planned construction. Also, remember that most of the points above pertain to cockroaches as well as rodents, but you must alter some steps depending on the species of cockroaches involved. Inspections are never stagnant. They grow and change with the situation at hand.

You can reach Dr. Frishman, an industry consultant since 1967 and president of AMF Pest Management Services, at


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