Multiple Catch Traps

Hundreds of thousands of multiple catch mouse traps (MCTs) are serviced every month inside food plants, warehouses and many other commercial institutions. The majority of these traps are installed and serviced by pest management professionals and in-house personnel of the larger food plant facilities.

Because MCTs have been used inside many different accounts by many different individuals over many years, a multitude of different opinions have emerged as to how these traps work and how they should be installed and serviced. Moreover, there is no shortage of myths surrounding the use of MCTs. So, let’s examine some of the science and the practical use of MCTs and attempt to dispel the myths.

Why mice enter MCTs. Because the house mouse is a major prey species it must limit the time it is exposed to predators. Upon entering a completely new environment (e.g., a warehouse), among new smells, sounds and the lack of natural vegetative cover, a mouse is likely to perceive a hole in the side of a metal or plastic box as an attrac-tive opportunity to "duck" for protective cover. Additionally, the nature of the mouse is to be investigative and opportunistic in locating resources and thus the mouse will explore new burrow holes for potential nesting sites. People often simplify this behavior and refer to it as "curiosity" and thus multiple catch traps are commonly referred to as "curiosity traps."

Cause of Death. What causes a trapped mouse to die inside a MCT? Often the terms "trap stress starvation," thirst and deprivation are used to describe the cause of death. Although some of these factors might play a role in some cases (depending on the specific situation), many mice die as a result of hypothermia — a loss of body heat. This is because small mammals have a high surface-volume to body mass ratio and thus lose body heat rapidly if they do not have the insulated protection of either a ground or structural nest or have some material (e.g., grass, paper, leaves, etc.) in which to construct a nest.

The rate of the hypothermia will depend on ambient temperatures of the floor and air surrounding a particular trap. A mouse captured inside a metal mouse trap by a warehouse bay door during the winter is likely to succumb after only a few hours. But a mouse trapped inside a heated building during the summer might live for a day or more. Other factors, such as the age and physiological health of a particular mouse, will affect the mouse’s longevity. In cases when two mice are trapped alive at the same time, the stronger mouse usually kills and consumes the weaker mouse to obtain food and maintain body heat.

Trap Servicing Issues. The frequency of when multiple catch traps are serviced depends on the specifics of a particular account. In the majority of commercial food plants and warehouses, MCTs should be inspected and serviced on a weekly basis. In some sensitive accounts and/or unique situations, traps (or at least certain groups of traps) may need to be checked twice weekly. Traps need to be checked this frequently when abundant exterior vegetation surrounds a plant and doors need to be left open for prolonged periods both night and day due to constant shipping and receiving. Often this is done by in-house personnel because the cost of contracting this frequent servicing out to a pest management company can be expensive.

In non-sensitive accounts and situations, longer servicing frequencies may be acceptable. Inside utility rooms of commercial accounts, non-food warehouses and other non-sensitive accounts, it may be completely acceptable to inspect the traps on a biweekly or even a monthly basis. Once a trap becomes "dirty" (containing feces, urine, hair or carcasses residues), the trap should be replaced or cleaned. Dirty traps should not be allowed to remain in any area of a food or pharmaceutical establishment. In most MCT models, glueboards can be installed inside the trap to facilitate easy removal of carcasses and the maintenance of clean traps. This is especially practical in those accounts where the traps are only serviced biweekly or monthly.

Trap Spacing. In food warehouses and similar accounts, MCTs typically are spaced 20 to 30 feet apart. Some food industry inspection organizations that play important roles in food safety programs (e.g., AIB, ASI, etc.) suggest specific distances in their guidelines. These guidelines provide for good general protective coverage. Does it matter from a scientific aspect whether traps are spaced 20 feet vs. 23 feet, or even 31 feet? Personally, I’m not concerned in warehouses that are kept clean and have rodent-proofed doors whether the trap spacings are every 25 feet or even 30 feet apart. Alternatively, in warehouses where perhaps heavy mouse pressure exists on the outside and where doors are constantly open, the minimum spacing distance of 20 feet is strongly recommended. MCTs need not be installed along interior walls unless there is some history of mouse activity along those interior areas or due to some other operational factor within the particular account.

For continuous shipping/receiving bay door wall areas, one trap on either side of every door might be excessive for those accounts with low mouse pressure. In most cases, 20-foot trap spacings along these areas, regardless of the door arrangements, will provide sufficient protection unless some particular incoming products are prone to mouse infestations, dictating more protection.

For bulk receiving bays (e.g., bulk rail and trailer tank cars, etc.), such areas are more vulnerable to possible mouse entry because the large bay doors commonly remain open for prolonged periods during the unloading processes (despite recommendations to the contrary). These areas should always have traps properly placed flanking both sides the bay doors and for double bays, one trap in the middle as well.

Traps should also line the interior side and back walls of all receiving bays. Exterior trap stations (e.g., bait stations containing snap traps in place of baits) should also be positioned on the outside walls flanking the bay doors. Unfortunately, some warehouse and food plant personnel mistakenly believe that because there are MCTs in place, they are "protected" should mice enter the plant during shipping and receiving operations. As a result, they become lax on closing the bay doors. But MCTs are only an additional tool for helping to catch an incoming mouse. There is no guarantee every mouse entering a warehouse or plant will venture into even the best-placed mouse trap. So, the important point is that large bay doors should remain open only during the period that trucks are passing through the bay doors. Of course, the whole point is moot if the bay doors are not rodent-proofed to begin with.

a Live Mouse. Obviously, maintaining a glueboard inside the MCT eliminates the annoying delay of dealing with a live mouse inside the trap. For those traps where glueboards are not used inside the trap, a live mouse can be disposed of by removing the trap from the premises and emptying the live mouse into a box or tall pail containing a glueboard. Never empty a live mouse into a toilet bowl. Not only is this an unacceptable and unprofessional method of killing a mammal pest, but mice are quite adept at escaping during these attempts and can re-infest the account.

Summary. Multiple catch traps are effective tools for minimizing the chances of mice becoming established inside our food plants and warehouses. But we should keep in mind that Mother Nature is constantly changing and presenting us with many different scenarios. We too must be flexible and remember the best use of MCTs is based on a combination of common sense, science and the specific operations of each account.