The Pest Control Technology (PCT) magazine article, “Exclusion Essentials” by Christopher Cushing, is a comprehensive guide to rodent exclusion strategies that draws on the concepts of Bob Corrigan, one of the world’s foremost authorities on rodent management.
The article emphasises that the foundation of successful rodent control lies in understanding rodent behaviour, physical abilities, and the importance of proactive exclusion.
This blog post is an in-depth exploration of the article’s key themes, practical recommendations, and technical insights into rodent exclusion.
The article focuses on rodent exclusion, preventing mice and rats from entering buildings. It asserts that exclusion is not merely a supplementary activity but the cornerstone of integrated rodent management (IRM).
Rather than reactively trapping or baiting rodents after they enter, exclusion focuses on identifying and eliminating potential entry points and structural vulnerabilities.
Understanding Rodent Physical Abilities
Rodents are exceptionally resourceful creatures with physical and cognitive adaptations that make their exclusion a challenge.
- Their bodies are well-suited for infiltration, as they are skilled swimmers capable of traversing waterways to reach new harbourages or to invade sewers.
- Rodents can climb vertical walls and textured surfaces, scale pipes, cables, and even rough brickwork with astonishing agility.
- Their jumping ability is impressive: mice can leap up to 30 centimetres vertically, while rats can jump over 60 centimetres.
- Rodents can drop from significant heights without injury, using their flexible bodies and tails for balance and shock absorption.
- Rodents can squeeze through incredibly small spaces, with mice passing through holes as narrow as 6 millimetres, or a pencil’s diameter, while rats require only 12 millimetres.
Rodents’ physical ability is rooted in their physiology, as both mice and rats possess tubular, flexible bodies and can contort their spines. If a rodent’s head can fit through a gap, the rest of the body can usually follow.
The National Pest Management Association (NPMA) video, Rodents: From Head To Tail, beautifully captures facts about rodents that highlight their anatomy and abilities.
Specialised anatomical features aid rodent entry feats.
- Rodents’ long, tapering muzzles, covered with vibrissae or sensitive whiskers, provide tactile feedback, letting them probe, explore, and evaluate gaps, cracks, and crevices.
- The fine hair on their ears contributes to their spatial awareness, helping them decide whether enter a space.
- Their intelligence further enhances their adaptability as they learn from past experiences and strategise to find alternative entry routes when faced with obstacles.
When burrowing is necessary, rodents use their muzzles and strong incisors to dig beneath hard objects like stones and rocks, or to gnaw through barriers such as wood, plastic, and even some metals.
Where burrowing is not possible, like where a door meets a concrete floor, rodents will use their powerful, ever-growing incisors to chew through wood, vinyl, or even softer metals, creating new entry points.
Recognising Rodent Signs and Vulnerabilities
Despite their stealth, rodents inevitably leave signs of their presence. Effective pest management professionals (PMPs) recognise these clues, which include:
- Dark, greasy rub marks (sebum) are left along frequently used pathways or at entry points, which appear like streaks of burnt oil.
- Gnaw marks on wood, plastic, and other materials. The width of these marks can differentiate species: approximately 2 millimetres for mice and about 4 millimetres for rats.
- Droppings, urine stains, and nesting materials.
- Structural damage, such as chewed doors, gnawed cables, and widened gaps around pipes or vents.
Identification of rodent signs is critical for planning their exclusion. PMPs must be more observant than building owners or maintenance staff, who often overlook subtle structural vulnerabilities allowing rodent access.
For example, a small, overlooked gap beneath a door or an unsealed opening where utilities enter a building can begin a rodent infestation.
Bob Corrigan’s Four Rodent Vulnerabilities
Corrigan categorises the vulnerabilities rodents most exploit into four types:
- Gaps at Ground Level: Mice and rats enter buildings through gaps around doors, damaged thresholds, and cracks in foundation walls. Open doors are obvious entryways, but rodents can breach even closed doors when they are not fitted with rodent-proof seals or have sustained damage for a long time. Gaps beneath doors without protective rodent seals are highly vulnerable.
- Gaps at Roof Level: Roof rats, known for their climbing ability, use overhanging branches, pipes, and utility lines to access roofs. Once on the roof, they take advantage of broken tiles, unscreened vents, or gaps in the soffit to descend into the structure.
- Holes for Service Penetrations: Utility entry points, such as holes for pipes, cables, and conduits, are among the common rodent entry routes. Even when these holes are partially filled with foam or caulk, rodents may gnaw through the material or exploit any gaps around its edges for entry.
- Small Spaces and Crevices: Rodents’ curiosity drives them to explore every nook and cranny. Their muzzles, with sensitive whiskers, allow them to feel their way around and determine a space’s navigability. Also, they don’t move only by instinct but by active sensory investigation. If a rodent’s head can fit, its body will follow, which underscores the need for meticulous exclusion.
The Importance of the Right Rodent Proofing Materials and Techniques
A common misconception in the United States of America is that vinyl weatherstripping is sufficient for rodent-proofing. While weather stripping is effective against drafts and insects, its soft, pliable composition is no match for rodent gnawing power. Mice and rats can quickly chew through vinyl, rubber, and plastics.
Corrigan recommends materials that offer true rodent resistance. High-density nylon bristle strips are effective at excluding mice due to their fine, tightly packed bristles. For more robust protection against rats, Corrigan advocates for rubber-encased steel fabric (RESF), a composite of steel mesh in a rubber sheath. It is highly gnaw-resistant and a formidable barrier at door bottoms and at openings in walls around pipes.
Precision is paramount in rodent exclusion. PMPs must carefully measure gaps and holes, and assess their accessibility to mice or rats. Gaps of 6 millimetres or wider let mice enter, while gaps of at least 12 millimetres let rats enter. Using the right proofing material for each type of opening ensures effective, long-lasting rodent exclusion.
Polyurethane foam is frequently used in the U.S.A for sealing gaps because it is easy to apply. However, on its own, it is susceptible to rodent gnawing and is not a long-lasting solution. Corrigan suggests that foam is effective when combined with stainless steel mesh and sealant. A layered approach of foam for filling, mesh for reinforcement, and sealant for weather resistance results in a more durable rodent barrier than foam alone. Caulk is also not a recommended rodent-proofing product, as, despite manufacturers’ claims, most caulks can be breached by determined rodents.
Exclusion and Sanitation: A Dual Approach to Rodent Management
Rodent exclusion is not just about closing gaps; it is about maintaining a comprehensive, proactive defence system. Rodents are notorious vectors and reservoirs of disease, carrying ectoparasites such as fleas, ticks, and lice, as well as pathogens including bacteria and viruses. Even after rodents are trapped and removed, their hairs, urine, faeces, and carcasses pose health hazards. Hence, exclusion must be combined with sanitation.
Corrigan’s dictum-“Pest proofing is pest prevention, and sanitation is pest control” captures this synergy.
Keeping storage areas organised, promptly disposing of waste, and cleaning up after rodent infestations are as important as physical exclusion.
Product Availability and Regional Considerations
In India, specialised rodent-proofing materials such as RESF are unavailable. However, the rodent-proof fabric, branded Rodent Proof, is available from Giridhar Pai Associates LLP (GPA).
GPA also offers the RodeXit All-In-One rodent seal to close gaps beneath doors and shutters, serving as an effective rodent entry barrier.
PMPs and building owners may source and use GPA’s specialised materials for effective rodent prevention.
Conclusion
Christopher Cushing’s PCT article, “Exclusion Essentials,” which relies on Bob Corrigan’s concepts, establishes that rodent exclusion is the most effective and sustainable method of rodent control.
Mastery of rodent exclusion requires a thorough understanding of rodent biology and behaviour, the ability to identify and address structural vulnerabilities of buildings, the use of appropriate materials, and a commitment to ongoing sanitation.
By combining the above elements, PMPs can protect properties and public health from the persistent rodent threats.