I sat across from the table as the gentleman explained his predicament. “Joe,” he said, “we have been dealing with an odor from this closet for years. It’s there for a week or two, then fades. But then it comes back. We’ve had numerous people out to troubleshoot the source of the odor. No one has been able to get to the bottom of it.”
“What have you tried so far?” I asked.
“We have obviously removed everything from the closet...multiple times. We’ve had plumbers, roofers, and heating and cooling techs troubleshoot it, but nothing adds up.”
The gentleman gave me a tour of the closet area, surrounding rooms, the basement beneath, and I walked the attic. We sat back down at the table and I asked if they had any history of mice. “None that we know of.”
“I think I know the source, and I have a way to test it if you can give me 30 minutes.”
And with his permission granted I grabbed my gear and proceeded into the closet. A few minutes later I had successfully removed five dead mice from inside the wall. Mice had been living in the attic and over the years, one by one, they had fallen into the wall void. Unable to climb out, they perished and emanated an odor under the wall, passed the floor trim, and into the closet. With the source confirmed we were able to then address the perimeter of the house to permanently stop both the mouse intrusions and the stink. No odor since.
This story is a good reminder of one of the problems associated with mice. Odor. A lingering foul smell. And in this case the customer didn’t know that mice were even getting in. This is common.
In this two part article we’ll be looking at some of the biology and ecology of mice to help unravel why they might target your home or business, and some actionable steps to help reduce their presence.
Natural and Urban Habitats In talking about mice, it is good to point out that there are multiple species in our area, including the House Mouse (Mus musculus), Deer Mouse (Peromyscus maniculatus), and White-footed Mouse (Peromyscus leucopus). While some of their differences are certainly notable, the issues they create in residential and business settings are similar enough that we’ll consider them as one group, unless otherwise noted.
Mice will live anywhere they can find the right combination of shelter and food. Many people who call requesting help with mice indicate that they don’t hear activity in the summer, but the noises pick up in the fall. During the warmer months, mice will often abandon their indoor lodging as they can find shelter closer to their outdoor food sources.
As the temperatures drop in the fall, they frantically gather food and create food caches. These caches are often brought indoors, providing sustenance for the winter. Mice will target nearly any structure that provides some level of shelter, whether it be a home, garage, shed, or even wood piles and the occasional outdoor grill.
Seasonal Activities
Mice are master explorers. They are excellent at climbing, and lay down trails of urine to mark travel paths. They are able to ascend and descend any surface which they can grip with their claws. They also can navigate in complete darkness due to their heightened use of their whiskers and ears—a combination of kinesthetic sensation and echolocation.
With all these inherent abilities it is no surprise that people encounter new activity throughout the year. However, there is validity in the observation that you are more likely to hear mice in the fall and winter months. As previously discussed, this is largely due to the outdoor food and shelter options becoming less reliable during the winter months.
If you have concerns about mice, contact Paw Control to share your concerns and discuss removal options.
It is worth noting that mice do not hibernate. Their activity levels stay strong during the winter months, requiring a steady intake of calories. This means that mice must continuously explore to locate and cache food throughout the winter months.
Food Preference
A mouse had been seen in the mud room next to the washer and dryer. The customer had seen it when she went to fill her dog’s food and water. “I saw the rodent zip under the washer, and that’s when I called you.”
I scanned the room and saw that the dog food was in a plastic, lock-top container. Good. I then noticed a floor register only a foot away from the dog bowl, and I became suspicious. I carefully pulled up the register cover and used a small inspection mirror to peer around the bend of the ductwork. And there I saw what I suspected: several handfuls of dog food, carefully stacked for later consumption.
Mice have a diverse palate. When living outdoors they favor seeds, berries, and cereal grains, as well as other plant material. Indoors, they will eat most human foods. While anything with caloric value is a target, mice prefer foods rich in fats, proteins, and sugars.
Quick tip: If you have mice raiding your pantry by going under the pantry door, you may be able to install a floor sweep to the back of the door to stop their entry. Alternatively, stuffing a towel under the door may do the trick. Of course, the best solution is to locate and seal all exterior entry points, rendering indoor work unnecessary.
Mice are omnivores. In addition to plant-based foods, they also consume insects and small invertebrates such as cockroaches, slugs, and snails. Mice will also cannibalize other mice. I’ve seen this commonly occur in two situations. First, a mouse that has already been killed in a snap trap will sometimes shows signs of having been cannibalized. Second, two or more mice trapped in an enclosure will eventually fight to the death. This is one of the down sides to live trapping using a multi catch trap. The trap must be checked often enough to prevent cannibalization.
Reproduction
Mice become sexually viable between 6-10 months after birth, depending upon the species. The deer mouse can have two to four litters per year. With a clutch size of three to five pups per litter, a mother can produce around twenty mice per year. A deer mouse can live up to four years, so one single mother could add eighty mice to the local population!
However, the deer mouse is a lightweight as compared to the house mouse. With the potential to produce six to ten litters per year, at five to six pups per litter, we see the possibility of sixty offspring per year. The house mouse has a lifespan of around two years, providing the potential for a single house mouse to rear 120 offspring.
Fortunately, these scenarios rarely occur because it would require a ecological carrying capacity that is unlikely.
The ecological carrying capacity describes the number of individuals within a local population that can survive in a defined area due to limited resources and competition. Common factors include the amount of food, water, and shelter available to the population. As food abundance increases, the carrying capacity will likely increase. Other factors include the presence and number of predators, social cues (some species will not tolerate large populations), and the local geography and climate trends.
We have covered several topics related to mice: their natural and urban habitats, seasonal activities, food preferences, and reproduction. This article considered mice from a biological and ecological angle. Part II of this article will focus on their overlap with humans: signs that they have infiltrated, disease and health risks, common types of damage, and tips to discourage their activity near your home.
Joe Taylor, M.S. Science Education, B.S. Biology, is a full time nuisance wildlife control operator in Eastern Iowa, and owner of Paw Control, LLC. Follow him on Twitter: @pawcontroller at LinkedIn, or the Paw Control blog: https://www.pawcontrol.com/blog
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