A review of rodent biology and habits, as well as a discussion of various control methods.
The nuisance wildlife control (NWCO) and pest management (PMP) industries would come to a grinding halt if it weren’t for the order Rodentia. From mice and chipmunks to woodchucks and beavers, there is plenty of work for all of us, especially since some of these species overlap. As a nuisance wildlife operator in New York state for the better part of two decades, I’ve dealt mostly with the larger species. But once the colder, wintry weather sets in, and some of these nuisance animals and pests aren’t as active, I start getting calls for mice. In many cases these little critters help me get through the slower winter months.
Mouse Info. Mice generally enter a house at a point low to the ground, and then make their way around through the walls and in many cases up to the attic. Look for rotted out frames for basement windows and doors, garage doors that don’t close all the way, cracks or holes in foundations, and dryer vents and air conditioning units that may have holes serving as mouse entry points. Most residences in New York state (and around the country) have mice at one time or another for a variety of reasons. In most cases, I find that mice look for ways into a residence in search of warmer areas, which explains why mouse jobs pick up later in the year. In order to figure out why this happens and to evaluate a given situation, let’s first take a look at some natural history.
Reproductive rates can offer a clue as to how many mice may be present, since we know gestation is less than a month and up to 10 litters may be born in a given year. During the summer, mice may have moved in at any time (although typically I find they stay outdoors where food is more abundant) so it’s entirely possible to have only one or two. But assuming that by winter a given population of mice already has found and made a home inside the house you are inspecting, that may indicate a larger population as the mice will have had time to produce at least one litter.
Mice and many smaller mammals have a fast metabolism, and for one good reason — heat retention. Call it a hazard to being warm blooded. Many small mammals like mice have much more surface area than volume, and that allows for more heat to escape than the low volume would retain. (In contrast, a whale would have a very low surface area compared to a high volume, meaning that whales retain a lot of heat, even in arctic waters.)
This means that mice have to continuously eat in order to maintain a constant body temperature, or find a place where a lack of warmth isn’t as much of an issue. That place, in most residential settings, is woven into the attic insulation of homes. Of course, the more a mouse eats, the more comes out the other end of the digestive system, which is an important factor in determining population, and thus designing an approach for subsequent removal from any residential dwelling.
Also important: mice generally have a home range of about 30 feet, meaning they spend their entire lives within a 30-foot diameter. This estimate is significant if while inspecting a residence you determine the entry point to be the garage, while at the same time you find droppings in the attic on the other side of the house. This can mean either the population is high and has expanded or there are other entrances on the other side of the house that were missed.
With these biological facts in mind, it is apparent that both NWCOs and PMPs must be skilled in determining and estimating the size of the mouse population, as that will certainly determine the abatement approach. In many cases, because of the rapid metabolism of mice, the number of droppings (and visual sightings) are not always accurate in estimating the population.
Once a determination is made relative to how many mice you are dealing with, it’s time to devise a solution to the problem. Fortunately there are dozens of effective methods for abating mice, from snap traps to multiple-catch traps and rodenticides to structural repairs of buildings. My advice is to try them all. The bottom line is that mouse abatement is all about versatility. Here are some of the pros and cons of the industry’s more popular methods:
|Clockwise from top left: Two of my standard set ups for mice in an attic using a combination of glue traps and snap traps. Photo #3 shows the parts of a standard snap trap, which are discussed below.
Snap traps. This age-old trap is still probably the best value on the market. A snap trap can be used over and over again. Obvious cons include snapping your fingers on occasion, but hopefully that should only happen once (if at all) to professionals. That said, when you first take a snap trap out of the package, you may have to adjust the “dog” that holds the pan in place (see photo on the right). As far as the pan goes, I prefer snap traps that have a wide yellow pan, ensuring enough bait can be used, such as peanut butter and/or sunflower seeds. These are great, especially for drop ceilings, where I may have to entice any mice to come to the trap. Also, the snap traps with larger yellow pans have a dog that “snaps” into place from the back of the device, making the trap more sensitive. This is opposed to some traps that have more narrow metal pans where the dog “snaps” from the side. With those types of snap traps, I find that not only can you place less bait, but these traps have a lot of “play” to them and allow for mice to lick bait away without setting off the trap.
I almost always use rat-sized snap traps, even for mice. However, I have used the smaller ones where space is prohibitive. In certain cases when I have to place these traps outdoors, I use a small cage trap, placing the snap inside using a stick to prop the door open about an inch or so to allow mice in, but at the same time preventing household pets and kids from getting “snapped.”
Glue traps. As with most types of mouse traps, there are many varieties of glue traps. And because they are a “consumable” and cannot be reused, you must factor in their cost. I have noticed over the years that glue traps contained in a plastic tray are not quite as sticky — I have often found mouse hairs in the glue but no mouse. Not to mention the fact that I have a more difficult time combining these with snap traps for a double set. I usually purchase glue traps that are simply made up of a piece of cardboard, stronger glue and are covered in wax paper until ready for use. These are generally cheaper, with better holding power and are easy to combine together to form a larger glue “mat” to cover a larger surface area. I have also combined glue traps with snap traps when I find that the mice are taking the bait on snap traps without setting them off. Also, the plain cardboard glue traps are obviously flatter and I can use them in areas with little space, such as underneath stoves and refrigerators. They can be folded into a triangular shape and placed against walls. There are times when glue traps also can snag single bats as well.
Multi-catch traps. Multi-catch traps are effective simply because, as the name suggests, they can catch multiple mice. They can be far more efficient, with fewer necessary trips to check and clean out any traps. Although there is certainly room for these traps in residential settings, it is rare you get such an infestation to as to warrant a multi-catch trap inside a home. Generally, I would use this type of trap in a commercial setting where the professional would have to catch many mice quickly. One of the best aspects of multi-catch traps is that for the most part, they are discreet — most folks just walk right by them without realizing what they are, or why they are there. Another pro is that the trapped mice — even though they may be alive — are contained and not visible to anyone. Generally, these traps have a spring-loaded ramp that depresses with the weight of a mouse, leaving the trap open. Once the mouse moves off the ramp, the ramp springs up again, preventing escape.
Rodenticides. I don’t have a pesticide applicator’s permit, so I do not apply rodenticides. I have found the process to obtain the necessary certification is not cost efficient for myself or my business. It is interesting to note that homeowners generally are allowed to apply rodenticides to their own property, but a nuisance wildlife control operator or pest management professional without the certification cannot do so on their behalf.
|Duct work in an attic can be the victim of mice and even flying squirrels who can chew through them.
A second reason I don’t use rodenticides is because most are anti-coagulants, meaning they cause internal bleeding. Once that rodenticide is consumed, the mouse could die anywhere, including areas that are inaccessible, which can bring on a new problem that probably didn’t exist previously: rotting carcasses.
My final reason for not using rodenticides is because I may never know or be sure if they have been effective — there can be any number of concurrent reasons for mice to leave a home, die or stay undetected in an attic. Showing a homeowner a captured mouse in a snap trap, although morbid in a sense, is much more effective. However, I do believe rodenticides can be effective away from the main structure (such as detached garages or barns) where you wouldn’t have to worry about a mouse that has ingested a rodenticide entering the home. You simply have to make sure the rodenticides are placed far away from pets and children. Rodenticides may also have a larger role in commercial settings where a dead mouse in the walls may not have the impact as inside a residential setting.
Ultrasonic devices. The use of ultrasonic devices also has become increasingly more popular, and as such, customers ask me about them from time to time. Their effectiveness is questionable. Basically, these products are supposed to use sound waves generated from wall outlets, making it undesirable for rodents to stay in a structure. Research over the years has shown these products are ineffective for rodent control.
Prevention. Once all the mice have been either trapped or otherwise removed, it is time to repair and prevent future occurrences. Although mice can cause some structural damage, it is rare that this damage will undermine the integrity of support beams. However, an infestation resulting in excessive droppings and urine may result in having to replace insulation and possibly ceiling tiles. If mice are getting inside near basement window frames, chances are those windows needed to be replaced prior to any subsequent mouse damage.
|A successful glue trap set near insulation inside a home.
The bottom line is, it really depends on how far you as a nuisance wildlife control operator or pest management professional want to go in making repairs. Generally, I leave structural repairs to those suited for contractual work and have business cards and recommendations for my customers. In most cases those types of repairs involve nothing more than using caulk, silicone, spray foam or cement to seal holes, although I have had to install hardware cloth screen and even had to put in ridge vent plugs to prevent access, so repairs do vary greatly from job to job. Still, there are jobs such as inside older homes and even commercial buildings that you simply can’t seal —offer extended warranties for additional trapping as the need arises.
Trapping and preventing mice from entering homes and businesses may not have all the glory of trapping beavers that prevent widespread flooding. But solving rodent issues prevents disease and food contamination. You give peace of mind to thousands of residents across the country, and allow businesses dependent on health department standards to thrive.
The author is owner of C&C Wildlife Management, Delmar, N.Y. He has an associate degree in wildlife technology from SUNY Cobleskill, and a bachelor’s degree in wildlife management from West Virginia University. E-mail him at firstname.lastname@example.org.