Model Behavior

Rodent Control Issue - Rodent Control Issue

Excerpts from rodent expert Bobby Corrigan’s presentation during PCT’s Rodent Control Virtual Conference.

August 11, 2016

Mice prefer warm areas in nooks and crannies, furniture and equipment voids, and overlooked boxes near food.

“It’s important to be aware of these facts: The house mouse, Norway rat and roof rat are rodent species that mature quickly and if infestations aren’t dealt with promptly and professionally, they can reproduce quickly and disperse significantly,” said rodent expert Robert “Bobby” Corrigan. “That makes for unhappy customers and frustrated PMPs. Professionals must understand the key rodent behaviors and how to use those behaviors against them. You can use as many chemicals as allowed, but unless you understand rodent behavior, you stand a good chance of not achieving optimum control."

Corrigan made these observations in his presentation, “Essential Rodent Biology & Behavior for Control,” which was part of PCT’s Second Annual Rodent Control Virtual Conference sponsored by Bell Laboratories. Corrigan knows what he’s talking about; he first worked as a pest control technician in New York City, then earned his Master of Science and Ph.D. degrees in rodent management from Purdue University. Now he runs his own consulting business, RMC Pest Management Consulting in Richmond, Ind. As such, Corrigan has been a force in the industry for more than 30 years.

SMALL BUT INCREDIBLE. “The house mouse is a small, but incredible mammal that generates a tremendous amount of rodent control revenue,” Corrigan told webinar participants. “It causes much damage, carries pathogens and attacks food supplies. Inadequate control of these creatures can drive pest controllers crazy.”

According to Corrigan, customers often expect mouse control to be done cheaply because it’s such a common pest, and there are so many companies offering mouse control. “But if PCOs charge less, they’re making a big mistake because they aren’t anticipating those inevitable callbacks,” he said.

Corrigan said rodents also are opportunistic in their foraging behavior. “They establish home ranges where they hunt for food repeatedly, and, within these ranges, they also set up territories which they will defend strongly.”

FOOD FOR THOUGHT. Compared to rats, mice don’t eat a lot, he said. A mouse will eat about one tenth of an ounce of food per day. Based on this knowledge, you should set out many traps or many placements of bait in small amounts.

“Rats, on the other hand, eat 1 to 3 ounces of food daily. They are also particular, striving for nutritional balance if they can find it. To attract a rat to a rat trap, use a variety of foods such as sardines, peanut butter, apples, etc.,” Corrigan said. “When using rodenticide bait, fewer placements with larger amounts of bait can be used. In general, try to identify ‘eating spots’ as well. Rodents may cache food in these safe spots and can use pheromones to help mark their locations.”

The home range of a mouse can stretch 10 to 30 feet or more. That of a rat in city streets can stretch 90 to 450 feet, he said, explaining that the reason there is such a wide diversity in distance is simply because when food is abundant, the rodent will stay closer to that source. When it is scarce, home ranges can increase.

If you learn where those home ranges are, he said, that will enhance your monitoring activity and generate correct use of bait stations, traps and inspections.

NESTING AND FORAGING AREAS. There are some “typical” nesting and foraging areas of mice and rats — as well as some “non-typical” areas that pest control professionals must look for, Corrigan said. First, understand where the rodent likes to nest. Mice prefer warm areas in structural nooks and crannies, furniture and equipment voids, and overlooked boxes near food.

“Rats need bigger spaces, and indoors, concrete hollow block walls can become virtual rodent condos,” he said. Rats that live outside prefer available earthen spaces. That is, they prefer to live in and around healthy dirt. If you’re investigating an outdoor rat problem, look for healthy plants and shrubs that are cavernous in shape — this is where you are likely to encounter a rat burrow. A burrow is typically about 4 to 6 feet in length with up to three holes, he said. “This knowledge reduces the need to treat each hole. Just one application at the main entrance of each burrow system should suffice.”

TRAVEL-WAYS. What about rodent travel-ways? Rodents often travel along linear paths, such as shadowy lines along walls, pipes and landscape edges, and they mark these paths with pheromones. “When identifying potential pathways, be aware of sight, smell and kinesthetics [the sensation of movement or strain in muscles],” he said. “The latter is so important because, if we can determine their memorized path, we can then target these areas accordingly.”

Although some rodents travel along walls, rodents in some colonies may not, or they may not for various lengths of time for a variety of reasons. “A common misconception, or half-truth, is that they always travel along walls because they can’t see well,” Corrigan said, explaining that there are environmental/structural aspects that trigger rodent foraging behavior and offer clues for their control, including corners, quiet areas, structural voids and squeeze holes. “Awareness of these triggers is more effective in finding rodents much faster than just looking for tell-tale droppings,” he said. “Does finding droppings mean there are rodents always close by? Not necessarily.” So it is important to be aware of the active signs rodents leave in combination with the environmental and structural triggers present in any rodent-infested building or area.

AWARENESS OF ENTRY POINTS. Corrigan suggested that technicians be aware of entry points. “Once rodents get into a building, others can follow by sensing rodent pheromones, which are a critical part of the science of rodent behavior,” he said. “Pheromones are always in play, for example, in marking favorite spots. It’s our job as pest experts to know how to find these spots and deal with them quickly.”

According to Corrigan, rodent behaviors are complex. “Their actions, of course, vary — sometimes in the same building or in the same block. It all depends on the particular colony, or it can depend on such factors as what’s in a rodent mother’s milk, or what’s found in junk piles, or emulating their mother’s or colony members’ actions.

“You can go from one area to another and see signs of different sets of complex rodent activities. These observations should help you determine what rodent control actions you can take — that’s what distinguishes us as professionals,” Corrigan said. “The take-home message is, if you’re simply placing traps or baits only along walls in every account, that’s not always going to work, or it may not work as quickly as it could, had better attention to detail been considered. That’s key to remember.”

Never assume that there is a single standard rodent behavior, or that you can perform rodent control the same way in every situation.

You should never assume there is a single standard rodent behavior, and that you can, therefore, perform rodent control the same way in every situation, he said. Not only is that not professional behavior, but it won’t always solve the problem in a timely manner. “As pest professionals,” Corrigan said, “it’s our responsibility to be aware of the complexities involved in correcting a rodent problem as fast as possible.”

FAST-GROWING POPULATIONS. As Corrigan explained, “From a rodent’s standpoint, the availability of tasty food, a good supply of that food and conducive surroundings encourage fast-growing rodent populations. Healthy rodent offspring means a rapidly increasing population — and before you know it, your phone is ringing and the person at the other end of the line is complaining about a major infestation.”

He also stressed that understanding the sexual maturity of rodents is important. If you’re not thorough in early control procedures, you run the risk of additional young being produced; they, in turn, can quickly reach their own sexual maturity causing future callbacks.

“During sales calls, initial customer visits and cleanouts, you want to be knowledgeable and able to truly determine the scope of the infestation. Is it minor, moderate or severe?” he said. “Sometimes a customer will want to know the exact number of rodents that comprise the infestation. There’s no way of knowing this, but most professionals can usually gauge minor or severe infestations.” If the infestation is major, the reproductive cycle is already rolling by the time you make your first visit. “So you’ve got to be very thorough to shut down that particular component.”

CAUSE OF CALLBACKS. It is important that the pest control professional realize that a house mouse can reach sexual maturity at six to eight weeks of age, and then begin producing its own pups in about a month. “It’s not surprising then, that the house mouse is one of the leading causes of callbacks,” Corrigan said.

In the same way, knowledge of the sexual maturity characteristics of roof and Norway rats is important. For rats, maturity arrives about three months after birth. As a result, he said, “depending on the size of a particular infestation, rodent numbers can get away from you if you’re not careful or thorough enough in control efforts.”

High populations of offspring bring about big consequences, the most damaging of which is dispersal, he said. When large numbers of rodents increase quickly in small areas, things can get crowded, and the young will be forced out to seek new spaces — causing new infestations in previously uninfested areas.

Another key consequence is the massive amount of pheromones they’ll deposit, Corrigan said, which may attract even more invading rodents to explore around the building. Finally, the larger the size of the infestation, the more rodents there may be that are trap shy, or bait station shy, which increases the chances of more callbacks.

“And therein lies the important financial aspect to this. Of course, you want to make as high a profit as possible in your rodent control business.” But, he said, “A common portion of the pest business that threatens high profits are unexpected callbacks. And these often occur when PMPs aren’t thorough enough on the initial end of the job, or not knowledgeable enough about the behavior of these wily mammals.” As such, Corrigan said he hopes a word to the wise about the biology and behavior of rodents will result in better, more accurate and more profitable rodent control.

The author is a contributing PCT writer and can be contacted at