Exterior Rodent Trapping Programs

Conventionally, exterior rodent control programs for commercial warehouses and food plants are made up of exterior bait stations along fence rows and exterior wall perimeters. But baits are not the only option available for commercial programs. Various types of trapping programs can be substituted for those accounts that desire less pesticide use around their facilities or want “recovery” of those rodents interacting with their facility. Let’s examine exterior trapping programs a bit closer.

SNAP TRAPS INSIDE BAIT BOXES. Monthly rodent pressure on commercial accounts ranges from nil to constant, depending on various environmental factors. Of course, the accounts that experience very minor to no rodent pressure still require exterior programs that protect them should the incidental mouse happen along. But, for the PCO on these accounts, a program that also facilitates easy inspection is an attractive goal. Snap trap stations could accommodate these accounts.

Snap traps for mice can be installed inside conventional tamper-resistant rat-size bait stations and positioned along the traditional spacing and locations around food plant and warehouse facilities. Some bait stations are now available (Aegis stations) with clear lids facilitating easy inspection. Depending on the particular bait station, the snap traps can be installed within the station’s bait holding compartments or the station’s entry ways. To provide backup (or ensure multiple captures should they be needed) setting two traps per station is recommended. A drop or two of peanut oil, or a smudge of peanut butter on the mouse trap will serve as the attractant. Or, these baits can be placed onto a piece of wood or masonite and then placed within the inner-most compartment of the stations. This will facilitate the mice stepping onto the traps as they attempt to move toward the odor of the baits. The Snap-E quick-set, plastic-base mouse trap (Kness Manufacturing) and the Quick-Set (Woodstream) are plastic-based mouse traps that offer quick setting with one finger — a big plus when many trap stations need to be checked. Snap trap stations could also serve as a means by which to install ant baits, cockroach baits, cricket baits or slug baits for those areas needing control of these perimeter pests as well.

REPEATING CATCH, CURIOSITY TRAPS. All of the brands of multiple-catch mouse traps (i.e. “curiosity” traps) can also be used for exterior trapping programs. Some facilities use these traps outdoors placed at the same spacing as bait stations. Some even install the traps “alfresco” along their building perimeters and fence rows (i.e. without any protective boxes or cover). However, installing multiple-catch traps into another box or beneath a cover is recommended to ensure long-term effectiveness. Otherwise, the traps are subject to water, dirt, dust, leaf litter and the like getting into the traps and rendering them corroded, difficult to clean, or worse, causing them to jam. Moreover, a covered trap station visually presents more of a substantial rodent control program than multiple-catch traps sitting out on the ground unprotected.

Plunkett’s Pest Control Company, Minneapolis, Minn., installs their exterior Ketch-Alls into large size metal bait stations (the Rat Cafeteria made by Solvit Inc.). Kness has just introduced an exterior plastic cover that completely covers and snaps down onto their Ketch-All trap. If the interest in exterior trapping increases by the food and warehousing industry, perhaps other trap manufacturers (e.g. exterior covers for the Tin Cat) will follow suit.

The Kwik Katch repeating mouse trap by the Gremar Corporation is constructed of mostly molded heavy-duty plastic, and thus the body is not subject to corrosion or warped metal panels, both of which help facilitate quick inspections in moist or damp environments. An additional all-plastic repeating trap (Mini-mouser) is expected to be introduced any time by Kness. Still, these plastic traps would need protection from the elements if they were to be used for exterior trapping.

Despite these interesting developments, exterior trapping programs are not appropriate for every situation. This approach has advantages and disadvantages that are important for consideration by both the PCO and the client.

ADVANTAGES. Perhaps the greatest advantage to an exterior trap is that it stops the mouse prior to it entering the building. Mice that have been poisoned by an exterior bait may live for another three to seven days following their feeding. In this time, they may enter the building and will need to be recaptured to prevent them from dying in inaccessible areas or equipment, contaminating product or hiding in outgoing product and causing problems on the receiving end. Such mice have caused significant inconveniences for food manufacturers and warehouses over the years.

Trapping programs also reduce the overall amount of pesticide used for the facility’s pest management program. There are no pesticidal baits to discard and replace. Trapping programs also allow you to monitor the species of mice interacting with the property. Have the droppings seen in the exterior stations been from voles, shrews, deer mice, rats or house mice? Or perhaps even toads or large insects? Knowing the primary species interacting with the exterior walls and fences is important in management options and programs.

Furthermore, unvisited trap stations do not require any change or replacement of a trap, and trapping programs are time- and money-savers for those plants with low rodent pressure.

DISADVANTAGES. If snap traps are used, set-off traps obviously cannot capture any new rodents. PCOs can minimize this disadvantage by using two or more traps per station. Also, the disturbance of snap trap stations can prematurely set off the snap traps. Food inspectors may interpret a snapped trap as a miss instead of considering that a disturbance may have triggered the trap.

Along moist walls, and after wet days, the metal springs of snap traps may rust or break. In colder regions, snow and ice may render mechanical traps ineffective. Some companies remove their trap stations during this period, or switch to installing baits nearby vulnerable potential entryways. If curiosity traps are used, they must be kept clean and in good working order. It’s easier to clean bait boxes of rodent droppings than it is to clean curiosity traps of decaying carcasses. Thus, for facilities under constant mouse pressure, repeating curiosity traps may not be cost-effective due to the extra service time needed. Using plastic insert trays or glueboards inside the curiosity traps will facilitate quick removal of carcasses. Still, such facilities might receive better rodent protection with rodenticide baits, or a combination of baits and snap-trapping stations.

Once the exterior trapping program begins, some accounts want the traps checked as often as the interior traps (i.e. weekly), resulting in higher costs. If traps are not inspected and emptied regularly, during warm weather, decaying carcasses can attract flies and dermestids. For facilities under both rat and mouse pressure, standard exterior baiting targets both rodents, whereas exterior trapping is most suited for mouse control.

As we approach a future of reduced pesticide use for the food and warehousing industry, exterior trapping may be the right tool at the right time for some facilities.

Dr. Robert Corrigan is president of RMC Pest Management Consulting.