Commensal rodents rats and mice that depend on man for their food present complex problems to PCOs, and so require innovative pest management approaches to control them.
Commensal. The word is defined by Webster's dictionary as "of or relating to those who habitually eat together." Applied to "commensal" rats and mice, this term means the sharing of man's food, although most people certainly do not willingly share their food with rats or mice. The few species of rats and mice that are considered commensal not only share man's food, they often rely on man to shelter them, and have only proliferated with the help of man.
In the wild away from man's activities, rodents such as the Norway rat and the house mouse are rarely seen. It is only when man establishes his domiciles, crop fields, and cities that these rodents thrive. Herein lies the basis for controlling rodents utilizing an Innovative Pest Management (IPM) approach. The fact that these rodents are dependent on man to provide the conditions for proliferation allows for the quick reduction of rodent populations by altering or reducing those conditions.
EXTERIOR IS THE KEY. Probably the most common mistake when controlling a rodent infestation or in setting up a rodent control program is focusing too much of the rodent program inside the building. This is particularly true for many commercial buildings, where the threat of a rodent infestation is greater. Too often, the entire rodent management program consists of inside bait stations and a few traps coupled with a few exterior bait stations. This approach is usually doomed from the beginning, and will result in rodents being seen inside on a continual basis.
Rodent control has always been and should continue to be the best candidate for an IPM approach of any structural pest. Because preventing inside rodent infestations is the primary goal of a good rodent management program, non-pesticidal methods should play a major role in the program. When setting up the program, one must always begin outside because, except for a few instances, rats and mice invade buildings from the outside.
What needs to be done to limit or prevent rodent infestations? Man's activities provide rats and mice all they need to survive: food, water, and shelter. The more of these that are available, the greater the number of rodents that could potentially develop. At the heart of IPM for rodent management lies eliminating or limiting any or all of these necessities. By doing this, rodent populations outside near the building will hopefully be greatly reduced. Unfortunately, a customer's property that is well-kept may be bordered by a property where rodents are thriving. This situation will make any rodent management program more difficult, and control efforts will need to be increased.
THE SURVEY. Before a rodent management program can be established, the building must be surveyed for rodent activity and for the presence of conditions that might contribute to the rodents' survival. A diagram of the building and its surroundings should be completed, and evidence of rodent activity and contributing conditions should be noted on the diagram. If the facility has previous pest control records available, record any mention of rodent activity on the diagram.
Completing these two tasks allows the determination of the high-risk areas for rodent activity either due to the presence of contributing conditions or the actual data showing where rodents were captured. Determining the rodent high-risk areas is critical to the successful design and implementation of a rodent management program.
For example, a warehouse sits adjacent to a field of tall grass and a railroad track at one side. The other three sides are concrete driveways and parking lots. Where is the high-risk area for this building? Obviously, the side with the field and railroad tracks presents the highest risk.
Another example reveals, after the survey and review of previous rodent control data, that two sides of a warehouse seem to be where the majority of mice are captured. Further examination reveals that these sides are where bird seed and pet foods are stored. The highest risk areas for mouse activity in this building are these two sites.
Once the high-risk areas have been established, the rodent management program will focus a good deal of its efforts on those areas both inside and outside.
EXTERIOR CONTROL DEVICES. Even the best efforts to eliminate potential rodent harborages and improve sanitation are unable to stop some rodents from entering onto a property and venturing up to the building. For this reason, efforts must be made to capture or kill rodents before they can make it into the building.
The best method for dealing with rodents outside is the placement of exterior bait stations. When thinking IPM, minimal use of rodenticides is the goal, but in this case, rodenticides most likely will be necessary. Remember, the object is to keep rodents from gaining access into the building. The more rodents that make it to the building, the greater the chances that one or more will enter the building.
Multiple-catch traps could be used outside to serve as attractive shelter for mice and to catch them before they can enter a building. Tin Cats may be the best choice for outdoor use because they have fewer moving parts; however, a windup trap like the Ketch-All, the Mouse Master, or the Kwik Catch can be used. The Kwik Catch's plastic construction could be a plus outside, because it will better endure the effects of weather. The problem with such traps outside is that they will often catch other animals such as toads, snakes, and small birds. They are better used next to the building, particularly around doorways, under loading docks, and in similar protected areas. Away from the building, bait stations may provide the best answer for preventive mouse control outside.
Which traps can be used for rats outside? Snap traps? Glue traps? Live traps? First and foremost, rats are difficult to catch with any trap. Glue traps are likely not much use outside because they are likely to be exposed to wet and dirty conditions. Live traps require too much attention and effort to use long-term. Snap traps provide a danger of death or injury to nontarget animals and birds. Protective boxes in which rat snap traps can be placed and secured by locks have been used with some success, but, like live traps, snap traps take considerable effort to maintain outside. When rats are an issue outside, rodenticide baits are generally the best answer for preventive control.
If baits are determined to be the best option outside, only tamper-resistant stations should be used, and these should be secured properly using stakes, screws, or patio blocks. The bait should also be secured inside the station to prevent rodents from dragging it outside the station. This can be done by using rodenticide blocks only, and wiring or gluing them into the station. Bait blocks can also be secured by drilling a hole inside the station into which a rod can be inserted. The bait blocks can then be placed onto the rod, where they will hang above the bottom of the station. The Bell Laboratories Protecta station has recently been modified to include rods to secure bait blocks.
The first place to put bait stations around a large warehouse facility or food plant is at the fence line, if one is present. It is very important to do this along fences that adjoin areas or situations where rodent activity is likely to be high. This will be the "first line of defense." A good rule of thumb is to place these stations about 75 feet apart along the fence, and closer than that next to high-risk areas for rodents. The goal here is to give wandering rodents a "food source"; however, this particular food source helps to thin the rodent population.
A line of bait stations placed about 50 feet apart should then be established next to the building's foundation to create a "second line of defense." The stations should be placed closer together along the sides of the building where (1) rodent activity is likely to be greater and (2) numerous potential entry points exist.
The use of rodenticides as a regular part of a rodent IPM program is necessary for the reasons discussed. This use is easier to accept in an IPM concept when the bait stations and the bait are both securely fastened.
RODENTS: KEEP OUT. No matter how extensive and well-designed the outside rodent control efforts, some rats and mice will make it to the building. Without these efforts, however, even more rodents could be present to possibly enter the building. Exclusion of rodents by rodent-proofing the building is possibly the most important component of any rodent management program, and serves as the "third line of defense" against rodent entry.
In one recent case observed by the author, a food processing plant had a well-designed and well-implemented exterior rodent management program. Yet, when inspecting the warehousing part of this plant, numerous dead mice were found along the walls inside. Because no bait was being utilized inside the facility, the mice likely were feeding in the outside bait stations prior to coming inside the building. The problem here was a rodent-proofing issue. The walls of the warehouse were a single sheet of aluminum siding that did not fit well at the bottom of the foundation. The numerous gaps that were present were allowing mice to enter. To a regulatory official, a dead mouse is still an indication of an active infestation. In this case, the carefully designed rodent control program ultimately failed because rodent-proofing efforts were lax.
Pest management professionals have always followed the motto, "Build them out." Accomplishing this is nearly impossible without the customer's assistance. In order to effectively rodent-proof a building, all openings ¼ inch or larger must be found and sealed because this is the smallest opening through which mice could enter. Finding all of the potential openings through which a mouse could enter is very difficult, and may be impossible in many buildings. Building rats out of a structure is a little easier.
Several factors affect rodent-proofing efforts. The most important of these is who does the rodent-proofing. The pest management professional has the primary responsibility for identifying likely rodent entry points. The professional must then either convince the customer to seal those entry points or sell them a service to rodent-proof the building. Small holes that are easily sealed should be the concern of the pest management professional, and he or she should go ahead and take care of these as part of the service. Larger issues such as weather-stripping and concrete and sheet metal work may better be left to the customer to complete.
The overall structural integrity of the building also affects rodent-proofing efforts. Older buildings obviously tend to have more potential rodent entry points than newer buildings. Buildings made of block and brick are often easier to rodent-proof than those made of wood materials or aluminum siding.
Open doors are always a key issue between the customer and the pest management professional. Warehouses are notorious for keeping doors open because so much of a warehouse's work requires that doors stay open. On the other hand, restaurants, hotels, hospitals, and similar buildings have no reason for keeping doors propped open, and the customer should be strongly advised to keep the doors shut.
Poorly installed or damaged weather-stripping on the bottom of doors is likely the most common entry point for rodents, particularly mice. It does no good to keep doors closed if rodents can easily enter under the doors. In addition, wooden doors should have metal kickplates at the bottom to discourage rodents from gnawing their way inside along the bottom corners of the door.
INTERIOR CONTROL EFFORTS. The interior portion of a preventive rodent management program is put in place to deal with the (hopefully few) rodents that still manage to enter despite the exterior bait stations and rodent-proofing efforts. If an active infestation is present indoors, more extensive control efforts will be needed.
• Sanitation. Sanitation is important inside (as well as outside) to limit food sources for rodents. This provides the benefit of forcing rodents to likely be more attracted to baits on snap traps, when these are used, and to rodenticide baits, when these need to be used.
As part of the sanitation program, storage practices have importance. Items need to be stored 12-18 inches from walls to allow for inspection and placement of rodent control devices. In warehouses, pallets should be stored to the extent possible so that enough space exists between back-to-back pallets to allow for inspection and placement of devices when these are necessary.
• Active Infestations. When rats or mice are present inside, it seems prudent that trapping should be the primary approach used in an IPM program or any rodent management program. Trapping begins removing rodents immediately, something that baits do not do. Trap results can be quantified as to numbers of rodents captured. The results with baits are much less certain because many, if not most, of the rodents killed by baits are not recovered. Remember: To eliminate a rat or mouse infestation, every rat and/or mouse must first interact with and then commit to one of the traps (or baits) placed. "Coaxing" the rodents to do this takes skill, experience, and persistence.
• Mice. For mouse control, snap traps, multiple-catch traps, and glue traps can be used, with the best results coming from the use of a variety of traps. The key is to use a lot of traps in the areas of mouse activity. The goal is to entice each mouse to interact with and commit to a trap. This will not occur overnight for every mouse in a facility, so almost daily follow-up visits are required to maintain the traps. Snap traps are often not widely used by many service technicians, but when used properly, snap traps will often catch more mice than other traps. Glue traps are likely to capture younger mice and should be used sparingly and also alternated with the other traps.
It is possible to eliminate many mouse infestations using traps alone. However, situations may occur where the use of bait stations is necessary to achieve elimination of a mouse infestation. Bait stations should be mixed in among the traps and placed in areas that are inaccessible to children and pets. A diagram should be drawn showing the location of all rodent control devices. This is necessary for all buildings, from homes to the largest food plants.
• Rats. Snap traps will be the best trap for capturing rats, although skill, time, and persistence will be needed to achieve elimination of a rat infestation. Pre-baiting traps will need to be done until the rats begin to interact with the traps; then the triggers can be set. Daily follow-up visits are a must when trapping rats to maintain the traps, remove captured rats, and re-bait traps. For rats, it is a good idea to use fresh baits on traps every day.
One technique with snap traps that can be used for rats does not require any baiting of the traps. Start by creating a "wall" using boxes or pallets next to a real wall where an active rat runway is present. Cut a 6 to 10 foot piece of plywood that is the width of the length of a rat snap trap. Glue, nail or screw snap traps with expanded triggers side-by-side on the board. Twenty traps or more may be used. .Place the board along this runway and set all the triggers on the traps.. The rat(s), if luck holds, will try to jump over the traps when they first encounter them, but should not be able to clear all of the traps. The false "wall" created by the boxes forces the rat to jump over the traps instead of going around them.
Glue traps can be used to capture rats, although, in the author's experience, self-made glue traps using bulk glue have been the most effective. A good backing for these self-made glue traps is black or brown roofing shingles. Shingles can be easily cut to fit into corners or areas where rats are running. Creating a glue trap several feet long to capture rats that try to jump over the trap is generally more effective. The thickness of the glue will take some experience to get "right" in order to effectively trap a rat.
Because rats are so difficult to trap, baits almost inevitably will also need to be used in a rat control program. Liquid baits can be very effective for rats (and also mice) if most other water sources are removed; however, liquid baiters should never be used in homes or apartments or outside where children or nontarget animals can access them.
The effectiveness of solid baits will depend on the availability of other foods. If a lot of food is available, it may be very difficult to attract rats to the baits. The best program for rats usually involves using traps and a lot of persistence, and in some situations, liquid baiters can be helpful.
CONCLUSION. Controlling rodents without using rodenticides can be accomplished in some situations, especially when dealing with mice. The key to effective long-term control of rodents lies outdoors, where efforts to attract as few rodents to a building as possible and then to build them out is the best preventive approach. Exterior bait stations in commercial situations may often be necessary to help reduce the numbers of rodents near the building. Rodent-proofing, however, remains the key point in preventive rodent management.
Once inside, infestations of both rats and mice can be quickly reduced using traps. But, in some situations, baits may be needed to achieve total elimination.
PCT contributing author Stoy A. Hedges is manager of technical services for Terminix International, Memphis, Tenn.
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INNOVATIVE PEST MANAGEMENT As a quick review, Innovative Pest Management stresses the minimal use of pesticides in this case, rodenticides to control an infestation of structural pests. One mouse or rat inside a home or business is one too many, so the "action threshold" is equal to one rodent. For this reason, any good rodent management program should concentrate on preventive measures. In most cases, the placement of rodenticides inside a building in response to sightings of rodents is taking action too late because the rodents are already inside the building. Preventive rodent control relies on the use of several methods, including the use of rodenticides, although nonpesticidal techniques should make up most of such a program. In some situations, the pest management professional may need to be truly "innovative" in his approach to addressing any current rodent infestation and preventing future ones. |
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HARBORAGE REMOVAL |
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Rodents need shelter to hide under, and the availability of large amounts of shelter is a primary factor in the development of large rodent populations around a building. In addition, potential harborages next to or near a building attract rodents to the building's vicinity. From there, it is just a short few steps into the building at the first opportunity. As many potential harborages as possible should be eliminated on the property surrounding the building. This is the first step in making the building as unattractive as possible for rodents. • Tall grass and other vegetation should be kept low-cut. • Landscaping should avoid the use of thick ground covers. • An 18-inch vegetation-free barrier should be established next to the building's foundation. • Piles of debris and items on the ground should be removed and not allowed to accumulate. • Stacks of pallets should be stored as far from the building as possible. • If economically feasible, the sides of drainage ditches should be covered with a thick layer of smallish gravel. This can reduce the use of this area as a burrowing site for rats, and also helps to prevent vegetative growth. |
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KEEPING IT CLEAN Sanitation, which emphasizes the reduction of food and water sources outside and inside a structure, is important in both limiting rodent populations and also attracting them to a building. Unfortunately, buildings in which food products are stored or prepared are likely to have plenty of available food for rats or mice. The key to sanitation is keeping food spillage to a minimum, removing food spillage as soon as possible, and handling food waste properly. Outside, the dumpster area is the critical sanitation area for most buildings. Facilities such as grain elevators and food plants that process grain have the additional concerns about grain spillage along railroad tracks and around grain silos. It is important in each of these situations to have a regular schedule for cleaning these areas to remove spilled food products. Additionally, if rats are a particular problem outside, the dumpster may require more frequent pickup and cleaning.  Explore the August 1995 IssueCheck out more from this issue and find your next story to read. Latest from Pest Control Technology
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