What Can We Do About Persistent Mouse Infestations in Multifamily Housing?

I recently had the opportunity to work with acclaimed rodentologist, Dr. Robert Corrigan, and learn about a particular tough type of mouse infestation found in multifamily housing, the “resident” mouse or “appliance” mouse. These are mice that live and breed within individual apartments or residences. Even when building maintenance staff and the pest control contractors do everything I typically recommend, this type of infestation persists. You can seal entryways from outside, seal access to wall voids around pipes and other utilities, use glue board traps, and place bait boxes with rodenticide around the buildings, without impacting the populations within individual apartments. The sealing, exclusion, and rodenticide placement can prevent new mice from entering the building but only have a minimal impact in reducing the mouse population inside already. Without Dr. Corrigan’s insight I would have been at a loss as to what further recommendations I could give beyond these typical management techniques.

With Dr. Corrigan's guidance I learned the breeding colonies in the apartments themselves need to be the focus of the pest management efforts. The real story behind a heavy mouse infestation has to be seen by visiting the apartments with the heaviest infestations. Dr. Corrigan always starts by asking the residents where they frequently see mice and for how long have they been seeing mice. The answers can provide guidance as to where pest management efforts should be applied. Dr. Corrigan calls these mice living within apartments “resident” or “appliance mice”. Often mice live in hard to access places like under refrigerators, in cabinet voids, and even in the open spaces under or inside couches, and most frequently in stoves. Upon inspection (pulling out the broiler drawer and opening up the top of the stove) evidence of mice nesting in the insulation in the sides of the stoves can easily be seen.

The telltale dark sebum stains and droppings can tell us where mice live and travel

While it’s common to see building management and maintenance staff at sites we visit doing a great job with exclusion, keeping common areas clean, managing trash, and hiring a reputable company to trap and bait with rodenticide, mouse infestations can persist because these efforts do not reach the mice living within the apartments. The mice find warm places to live in kitchens and happily raise their families with all the food they need within a few feet of their nests. Mice rarely live beyond 10 feet of their food source and can reproduce quite quickly under these hospitable conditions. Many people don’t realize the top of their ranges can be opened and cleaned. Regardless of the cleanliness of an apartments, under the stove top there is typically plenty of spilled food and the signs that mice are happily feasting undisturbed. When the broiler drawers are removed the signs of mice can be evident too. Often the insulation material from the sides of the stoves is pulled out. It makes excellent nesting material the mice certainly will take advantage of. Glue boards can be placed in these spots to monitor for mice but will not control them. Typically these traps will only catch a few mice and mostly juveniles. When we see juvenile mice on glue boards this is a good indication there is a nest nearby. There is a lot of work involved in eliminating the “resident mice” but it must be done to eliminate the allergens and multiple pathogens mice carry that can cause breathing problems and make the tenants sick.

Recommendations for “resident" mice include: 

For tenants:

1. Clean up food spills and have no food left out for the mice to eat, including pet food and the crumbs and spills on the floor from kids eating around the home.
2. Clean mouse droppings according to CDC recommendations – with a wet cloth and household disinfectants, not a vacuum. Wash in the washing machine in hot water any cloth items including blankets, rugs, and pillows which have evidence of mouse droppings. Steam any carpets with mouse urine or droppings. Before disturbing the droppings, make sure the home is well ventilated and masks and gloves are worn.  See the CDC’s recommendations here.
3. Avoid accumulating clutter. Clutter provides mice with more nesting areas and hiding spots. Extermination efforts cannot reach the mice hiding in boxes and personal belongings. Plastic bins and tubs can be utilized for storage to keep the mice out.
4. Use snap traps when possible to avoid having to handle live mice on glue boards. See How to set a snap trap at Stoppests.org

 For maintenance staff and pest control contractors:

1. Bait boxes alone won’t work outside and inside apartments especially when there is so much other food available. The mice will likely eat the easily accessible spilled food and crumbs before the bait.
2. Use exclusion materials which incorporate steel or copper fibers, and escutcheon plates, not just foam fillers. Even the “rodent-proof” foam will eventually be chewed through as mice look for ways to access people’s apartments and their food source and they will even use it for nesting material.
3. Appliances will have to be taken apart to physically remove the nests, droppings, and mice living in them (or replaced). Stove sides can be removed and the insulation can be replaced. As the contractors or maintenance staff work they can set up a ring of glue boards to catch the mice as they scatter out of the appliances. Personal protection is a must when working with mouse droppings (a mask and gloves at the very least). If vacuums are used, a HEPA filter vacuum must be used to avoid having the pathogens and allergens become airborne.
4. Judging from the evidence of droppings and the black smears mice leave along their trails you may find mice are living in inaccessible places. When licensed pest control technicians flush these areas out for cockroaches the mice will also be flushed out. A glue board “moat” must be used again. Once the mice are flushed out and removed entryways can be sealed with sealant and ideally an escutcheon plate is used around pipes and utilities.

See the StopPests Pests Solutions Rodents page for more information on rodents in multifamily housing.

Comments

[Juliea Huffaker]

Hi James! Mice can be difficult to control! Especially in apartment or multi family housing! We love using exclusion pest control techniques like caulking and wire meshes to fill holes.

[Susannah Krysko]

I'm just revisiting this post I wrote a few years ago and noticed I failed to mention glue boards are inhumane. The mice often take a while to die and in the process residents may hear them making sounds. It's not a good idea to let residents handle mice either but the mice on glue boards must be disposed of! so think about who is going to visit almost daily to check them!
-Susannah, [email protected]