[PCT Event] Mysteries of Rodent Control

Features - Industry Events

At PCT’s Advanced Rodent Control Virtual Conference, Bobby Corrigan told attendees they must train themselves to see what others overlook.

September 23, 2014

Perhaps you’ve read some of the Sherlock Holmes stories by Arthur Conan Doyle. Or maybe you’ve seen some of the movies or TV series starring Doyle’s fictional consulting detective. If so, you’d probably agree that what stands out about Holmes’ famous crime-solving abilities was his use of logical reasoning. But what does this have to do with advanced rodent control, the subject of a recent PCT Virtual Conference?

Dr. Bobby Corrigan, the expert who conducted the web-based conference, is strongly influenced by the Sherlock Holmes methodology. Corrigan reminds us that urban rodentology is, like most sciences, a complex subject. “The main characteristic that accounted for Holmes’ success,” Corrigan said, “was his ability to keenly observe for clues and use forensic science skills to solve difficult cases. If you utilize the same approach to rodent control, the greater the chance you will have for success.”

Be a Keen Observer.

Corrigan, who has been called the “Sherlock Holmes of rodent control” is president of RMC Pest Management Consulting and one of the country’s leading rodentologists. He worked as a pest control technician on Long Island before earning a Ph.D. in rodent control from Purdue University. In addition to running his own consulting company for the past 30+ years, he is a part-time research scientist for the New York City Department of Health helping officials with their ongoing war on rodents. As a result, he very much understands the practical challenges of controlling rodents in difficult urban environments.

“The Sherlock Holmes stories have taught me that when it comes to rodent control, you must train yourself to see what others overlook,” he said. “When you’re out on a rodent control stop, don’t take for granted that it’s just an ordinary stop. You’ve got to be a keen observer to learn what’s really needed.”

Carefully Analyze.

According to Corrigan, the best practice of urban pest management doesn’t lie with those who are best at using traps or baits, but rather with those who excel at keen observation, source finding, analyzing each unique pest situation, pest exclusion science and staying cutting-edge current to facilitate fast introduction of innovative research and technology.

Did You Miss the Event?

Were you unable to attend PCT’s “Advanced Rodent Control” Virtual Conference in March? If so, you can still see and hear all of the presentations by purchasing the webinar DVD from the PCT store.
     The webinar featured Dr. Robert Corrigan, a leading expert on rodent biology and behavior.  During this informative half-day program, Corrigan discussed how to identify the harborage sites and main travel ways of rodents in buildings; key factors to consider in commercial and residential settings when trapping rats and mice; and successful strategies for using baits and bait stations.
Call 800/456-0707 or visit www.pctonline.com/Advanced_
The event’s platinum sponsor was Bell Laboratories. Gold sponsors included Catchmaster, Earth Care Products and Syngenta.

“Analyze each pest situation carefully,” he suggested. “No two are alike. The concept shift for trendsetting IPM specialists is more towards being an investigator and less an applicator. The goal in rodent control isn’t to kill individual rodents, but rather to efficiently manage and where possible eliminate local rodent populations in an environmentally responsible fashion.” This can be done only with both an applied approach using situational analysis together with a sound understanding of the science behind rodent biology and behavior, he said.

“PMPs must understand the essential rodent behaviors and how to carefully use those behaviors against them. We can use as many chemicals as allowed, but unless we understand rodent behavior we may not achieve optimum control. We must be a thorough investigator, rather than just an applicator.”

The tremendous sense of smell that rodents have, he said, enables them to make major decisions through their nose. “And their whiskers (vibrissae) are ultra sophisticated. Just one bristle can give a rodent important information, such as judging the size of a hole. Rodents don’t possess great eyesight, but they can detect things that move (e.g., a predator) at relatively long distances. To further assist them in understanding their daily surroundings, rats and mice can memorize the amount of movement necessary (kinesthetics) for traveling from place to place.

“Callbacks that result from missed target applications of equipment or under-applying baits and traps can be expensive,” he said. “To be effective in rodent control, you’ve got to decide what the right thing to do is and then get it done in a timely fashion.”

In-the-field Tips.

Corrigan emphasized these points:

Rats along the exterior periphery of our buildings prefer burrowing into healthy soil because it provides good drainage and burrow microclimates. If investigating an exterior rat infestation, observe where healthy plants that create thick shadows and hang low or hug the ground are within close proximity to some food source (garbage cans, litter baskets, etc.). These are the likely zones for Norway rat burrow construction A typical rat burrow is about 4 to 6 feet in length with one main entrance and one or two escape holes. This knowledge will reduce the need to treat each hole.

Concerning rodent travel ways, rodents travel along linear systems: shadowy lines along walls, pipes and landscape edges, for example. Rodents mark these paths with various secretions which in turn contain pheromones. When identifying potential pathways, be aware of sight, smell and kinesthetics. Kinesthetics is important because if we can determine their memorized path we can then target these areas accordingly for bait and/or trap stations.

Understand the distance they travel. Home ranges for mice can stretch approximately 10 to 30 feet or more. The home range of a rat can stretch 90 to 450 feet. The reason there is such a wide range has to do with their local resources. When food is abundant nearby the nest, rodents tend to stay closer to that source. When food is scarce, home ranges can increase accordingly.

Understanding how rodents feed is obviously important. A mouse consumes about only 2 to 3 grams of food per day nibbling here and there over many places. Therefore, when baiting and trapping for mice, the golden rule is “many placements, small amounts.”


Feces & Rodent Communication

Rodents regularly urinate and defecate while moving about, as well as when pausing to rest, eat, drink or groom. And research has shown that urine is an important source of social odors by which rodents recognize each other and communicate within the colony. But what about feces? Do feces serve any useful function to rodents other than the elimination of wastes?

Research on Norway rats has shown that food sites with feces are more attractive to rats than sites without feces. They state that both feces and urine markings can act as stimuli, which effectively marks food sites and facilitates the communication of food preferences. Moreover, they claim that this communication can result in the social learning of food preferences. In other words, residual feces and urine deposits may actually assist in directing the rat’s attention to particular foods.

These researchers also suggest that rodents can pick up information about local diets by smelling and eating the feces of other rodents in the area. Both adult and young rats have been shown to ingest the feces of other rodents in their community. Young rats exhibited a preference for foods located near the feces or body odors of other rats.

This information is of considerable interest when we consider that most of rodenticide food baits used in rodent control are comprised of high-quality, food-grade cereals, which are in most cases highly palatable to rodents. And as most pest management professionals can attest, it is common to find rodent feces on, in, and around bait containers. Perhaps feces near rodent baits serve both to attract and entice other rodents to visit bait stations and sample the baits?

Source: Bobby Corrigan’s “Rodent Control: A Practical Guide for Pest Management Professionals.”


The rat, being much larger than the mouse, can consume from 1 to 3 ounces every 24 hours. Make fewer placements with larger amounts of bait. In general, try to identify “the favorite eating spots of the rats.” as well. Often such locations are marked with numerous droppings in one locale. To attract either species to traps, be sure to use a variety of foods instead of just relying on just one “old standby” (e.g., peanut butter). Match whatever the rodents have been feeding on as well as using the opposite food group, and then include sweets, moist foods and even soft materials that the rodent might collect for their nests.

Look for signs of high activity, warm spots, shadows, corners and voids. Don’t overlook cardboard storage areas as these are a favorite zone for mice and rats.

Before using bait stations or traps, eliminate or reduce any competing food sources. Otherwise, rodents may not respond strongly to your tools.

Exclusion is the best long-term rodent control technique. If they can’t get inside our buildings, they can’t be a problem. Be sure to incorporate exclusion products in your arsenal.


A Profile of Inner-City Mouse Populations

House mouse infestations within high-rise apartments and condominium complexes in inner-city areas are substantially different from the typical (and often minor) mouse infestation of suburban developments.

In those parts of our cities where house mouse populations are well established, the number of city mice is likely to be quite large and they are likely spread out over many city blocks. This is especially true of our older, densely populated cities such as New York, Boston, Philadelphia, Baltimore, Chicago, Miami and others. Mouse populations in these and many other cities pose chronic problems among many of our residential and commercial buildings.

But what factors render inner-city areas so vulnerable to chronic, perpetual mouse infestations? First, in all probability, mice in these areas have existed since the earliest days of the city itself. Many of the mice we are attempting to control today are descendants of mouse populations stretching way back. Second, inner-city areas are enormously complex structural environments. Consider the three-dimensional resource availability of the small mouse relative to nesting zones, protection from predators, finding food, and the hidden travel ways among the structural risers, and the various vertical and horizontal plumbing, heating and electrical chases. When cities are built and undergo literally thousands of structural renovations such as new buildings, remodeling, add-ons, etc., as well as city infrastructure improvements (sewers, utility systems, roadways, etc.), we create thousands of harborage spaces for mice (and sometimes for rats as well). From a practical aspect, most of these spaces remain inaccessible to us.

Because of the relatively large distances mice may travel during dispersal journeys seeking new harborages, as well as the many secretive travel pathways available to them, the immigration potential of the mouse into inner-city apartment and office complexes can be substantial depending on the size of local population. Thus, mice tend to “sprout up” like weeds in one apartment or another on a constant periodical basis. As each of these mice are killed by building occupants, others at a later time move to take their place.

Recognizing and understanding this city house mouse profile is important for two reasons. First, it has ramifications in the study of the house mouse relative to disease transmission.

Secondly, long-term control of mouse populations in city environments require a proactive and comprehensive program. Unfortunately, typical mouse control programs in city apartments, office complexes, restaurants and other city buildings tend to be reactive approaches of installing a trap or some bait when a mouse is spotted. Such efforts merely “harvest” mice off of the larger populations, rather than providing control with any real impact on the larger problem.

Trapping and baiting programs are important, but proactive programs also must include rodent-proofing programs of not only doors, but also utility systems leading into buildings and each apartment. It is the responsibility of the pest professional to illustrate to the apartment management what areas need repairs and rodent proofing. Of course, it is the responsibility of the management to address these issues. Expecting the pest professional to eliminate the mice from these urban environments without a total IPM approach is not realistic.

In city areas, with nearby high mouse populations, it really is the equivalent of attempting to bail out the ocean with a teaspoon. Certainly in homes containing allergen-sensitive individuals, harvesting programs will not suffice.

Source: Bobby Corrigan’s “Rodent Control: A Practical Guide for Pest Management Professionals.”


Nine more tips.

Corrigan suggested certain key words and concepts that rodent control investigators should keep in mind while being a keen observer on the job. Keep the following in mind:

  1. Lines. Rodents are hard wired to see and travel along lines.
  2. Warm areas. For mice, warmth is critical because small mice lose body heat rapidly and therefore look for warm areas, such as hollow walls. But rats often seek out warm walls and building voids as well.
  3. Shadows. Spotting shadowy areas; rodents will likely head for them.
  4. Corners. Rodents often gravitate towards corners where they receive high tactile feedback, making them feel safer.
  5. Voids. Rodents invade voids located in equipment, furniture and structural elements (walls, floors, ceilings) because they offer excellent concealment and nesting zones.
  6. Quiet zones. Areas that are located in quiet spots attract rodents. For instance, mice and cardboard boxes in a back storage room are a perfect fit.
  7. Sebum trails. The grease off a rodent’s body is called sebum and can be a telltale marking. “Remember, droppings and hair can be swept up by a client but sebum is often left behind providing you with the one clue you need to trace the rodents.
  8. Rodent droppings. This is the most obvious telltale marking of a rodent’s presence. But always try to analyze the dropping’s locations, arrangement, sizes and whether they are fresh or old. Droppings can be the “GPS” to help you perform your rodent work.
  9. Rodent hair. Yet another telltale marking, rodent hair from their underbellies is usually thick and light in color. Such hairs can be found on runways and stuck to the edges of holes in floors and walls — indicating that rodents are present at the time you are there investigating.


Final Thoughts.

Borrowing from a popular real estate slogan, rodent control is about “location, location, location.” It’s our job as pest management professionals to strategically bring traps and baits to where rodents are located.

Instead of simply placing our rodent control devices along walls and hoping and waiting for the rodents to find them, install your equipment in the high-activity spots that you know to be accurate because of your professional level investigation.


More About Rodents From Bobby Corrigan

After 30+ years in the urban and industrial pest management industries, well-known industry consultant Bobby Corrigan shares his extensive knowledge of commensal rodents in his “Rodent Control: A Practical Guide for Pest Management Professionals” hardcover book. “Rodent Control” provides a comprehensive look at commensal rodent biology and behavior and multiple approaches for their control.

The book:

  • Is fully dedicated to structural rodent control.
  • Was written especially for pest management professionals by a pest management professional.
  • Includes hundreds of color photos and illustrations of rarely captured rodent behavior.
  • Features 350+ pages of in-depth information on commensal rodent biology and behavior.
  • Is the most comprehensive book ever written on the subject for PCOs.

Chapters include:

  • Introduction To The Rodents
  • The Pest Significance of Commensal Rodents
  • The House Mouse
  • The Norway Rat
  • The Roof Rat
  • Deer Mice, Woodrats (Packrats) & Voles
  • Practical Rodent Inspections
  • Practical Sanitation Issues
  • Practical Rodent Exclusion
  • Rodent Traps & Other Non-Chemical Tools
  • Rodenticide Baits & Bait Stations
  • Rodent Pest Management in Homes & Apartment Complexes
  • Rodent Pest Management in Commercial Buildings
  • Rodent Pest Management in the Food and Warehousing Industry
  • Rodent Pest Management for Municipalities
  • Rodent IPM for Livestock Facilities
  • Challenging Rodent Control Situations

The list price is $49.95. To order, visit www.pctonline.com/store or call 800/456-0707.


The author is a freelance writer based in Milwaukee. Contact him via email at jfox@giemedia.com.