An Ounce of Exclusion is Worth a Pound of Cure

David Bennett

In previous articles, we have written about Integrated Pest Management (IPM), which is of great service to food processing industries, the health care industry, the residential apartment industry, and agriculture. IPM is a decision-making process that emphasizes prevention, knowledge of pest biology, and the use of least-disruptive control tactics, with pesticides saved as a last resort.

Exclusion is a preventative measure in IPM that seeks to stop rat and other rodent infestations before they begin. Methods of exclusion vary—making sure the outside of a building and the yard/property is free of trash, holes, cracks are repaired in foundations and windows, clearing brush or piles of refuse that rats can make homes in, discouraging burrowing, door sweeps, installing barriers that cannot be gnawed through around buildings, replacing cracked pipes and covering entry points, repairing cracked sidewalks, installing rat guards on drainpipes, and vertical wires—the list goes on. However, if a problem has begun already, it must be taken care of before exclusion can begin, or the animal, whether it be a raccoon, a squirrel, a rat or birds, can come back and totally destroy repairs in an effort to reclaim “their home.” There will be more about that later, but for the purposes of this article, we are concentrating on rats. Exclusion is at the forefront of the pest control industry and gaining impetus every day. Let’s look at some things that are necessary to understand exclusion and how you can use it to the best advantage.

Rodent Behavior

In order to fight rat infestations, it is critical to understand them and the reasons they have for moving into our homes and businesses. In a previous article we talked about how rats think—they process information almost exclusively from their whiskers. In the article referenced above, we quoted a grad student in the neuroscience program at the Huck Institute: “In fact, nearly a third of the rat’s sensorimotor cortex is devoted to processing whisker-related information, even though the whiskers occupy only one-third of one percent of the rat’s total body surface. In humans, nearly 40 percent of the entire cortex is devoted to processing visual information even though the eyes occupy a very tiny portion of our body’s surface.” They need those whiskers too, since they can fit into cracks and gaps the size of a quarter (about .96 inches) and they need to feel their way in the dark. But that doesn’t mean rats are blind! Dr. Vermaercke of Harvard University said they found in a study explored below that rats can recognize 3-D objects even if they have been turned. They can even tell the difference between a movie that features a rat and one that does not,so their visual acuity is much better than previously thought.

Of course, not all rats can fit in a space the size of a quarter. Large rats and overweight rats cannot (see the article about the fat rat who got stuck in a hole in a sewer lid!) Why do rats want to move in with us? Three reasons—food, shelter, and safe places to raise their young. Survival is a strong instinct we share with rats.

Enter Exclusion!

Environmentally sound and safe, exclusion is necessary component pest control. Pest control companies can lose business quickly if, after a job, the owner or resident finds just one rat—they will assume that the measures the pest control company took were not effective, and move on to the next company. And there are popular exclusion materials used that rats can, over time, overcome and bing, bam boom, your infestation returns. Food Quality and Safety explains, “A diligent plan, however, is only as effective as the barrier products installed. Caulk, mortar, and spray foam are occasionally recommended as exclusion tools. While appealing, given they are inexpensive and easy to install, these products offer little to no protection against rodents. A creature that can gnaw through lead pipes will certainly not be deterred by spray foam. Steel wool is another popular exclusion material. Though stronger than caulk and foam, steel wool faces rusting and decomposition over time and therefore requires regular replacement. Copper mesh, a more expensive solution, is effective against rodents when properly installed. However, this is not an easy task as a tight seal is difficult to secure, and the mesh often becomes loose over time. It is also a softer metal, lacking the sharp texture that discourages rodent gnawing.” You can’t use repellents in the food industry. What’s a company to do? There’s exclusion by design (for new structures and retrofitting for existing structures). San Francisco Environment has an excellent manual describing techniques for designing pests out of buildings called “Pest Protection by Design.” In this manual they are advocating many of the same exclusionary measures we have briefly discussed in a more comprehensive format. It is a guide for architects to help them design buildings that need a minimum of IPM measures. If it’s rat proof from the start, that certainly makes things much easier from a building maintenance point of view. But even buildings that are pest proofed by design need an IPM plan and need exclusionary measures.

Here’s a brief exclusion checklist (contact us to point you in right direction to develop a much more in-depth program designed for your individual needs).

Check for gaps in doors, windows, and cracks in foundations. Make note of all gaps and cracks you find, and fill them (see point 4), and repair them. Routinely inspect the premises and keep records of all repairs done so they can be rechecked (or presented to health authority inspectors as necessary for commercial industries). Records and inspections are your best friend! They are an integral part of IPM and necessary in a good IPM plan.
Remove potential food sources. Sanitation, sanitation, sanitation! Pick up trash. Use frequent trash removal service. Put it in rat proof sealed garbage cans. Industries of all kinds should put their dumpsters on concrete slabs.
Remove water availability. Take care of standing water issues. Gutters should be free of debris.
Bobby Corrigan, renowned rodent expert, advises this about doors in his article for PCTOnline, “Of Rodents and Doors,”(August 2015) : “One of the fastest ways to determine a door’s rodent vulnerability is to simply stand on the inside of a closed door with the lights out and look outward to check for any exterior light leaks. As a general rule, any light noticed at any part of the threshold and/or door corners is sufficient to require a ruler
Old warehouse loading dock inside

measurement if not immediate repairs. A final but important note on door inspections is to keep in mind that if the door materials at the thresholds and jamb corners contain “soft” materials, such as wood, vinyl strips or plastic bristles, rodents need only an edge of just 1 or 2 millimeters. Such tiny openings serve an exploring rodent as “gnaw-starts” for its incisors to enlarge the hole size to permit entry.” He recommends that jambs and thresholds be tight and flush and maintained monthly for commercial facilities. Corrigan advises rubber-encased steel fabric sweeps (RESF) (for areas with ongoing rodent activity or sensitive facilities where heavy protection is of utmost importance), or high-density brushes (HDB) (for heavily human trafficked areas with light rodent activity). For instance, rodent proofing strips are a formidable addition to your arsenal for rodent proofing doors, fences and walls, a steel encased polymer resistant to forklift damage, having a stainless-steel fastener rather than aluminum. Rats can’t chew through steel. The strips also cover gaps up to 1.4 inch (35 mm). When installing or repairing doors, Corrigan states that millimeters count since rodents can get in through small spaces.

Finally, it is recommended that exclusion be systematically applied. “Exclusion should be performed in a systematic way that is informed by your inspection. Minor pathways that are seldom traveled by rodents (no droppings, chew marks or sebum trails) should be sealed first, while primary pathways in the building should be targeted for population reduction (trapping) then sealed, once the population has been reduced. That means you use exclusion in tandem with traps, maintenance, sanitation, and regular inspections in your IPM program. Every building has different needs, and so a careful analysis of each individual building is necessary while designing your IPM program with exclusion and traps. We can help point you in the right direction Contact us for more information and any questions you might have. We’d love to hear from you!

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