“Commensal” Rodents Eat at Our Tables

Features - Pest Control

Rodents are intelligent creatures. They have been on Earth much longer than we have, and they’ve learned to adapt.

October 2, 2014

There are more than 2,000 species of rodents in the world, but it is the three defined as commensal rodents—house mice, Norway rats, and roof rats—that are of the greatest food safety and economic concern. Literally defined as “eating together at the same table,” commensal describes rodents that live among and are dependent on humans for their survival needs—food, water, and shelter. 

The High Cost of Rodents

Rodents can gnaw through a vast array of materials from window screens and rubber door sweeps to wood, fiberglass, plastic, drywall and some concrete. They enter buildings through gaps in foundations, around utility line entry points, under doors—including loading docks, and even beneath roofing tiles.

Rats can get in through a space as small as 1/2 inch. Mice need only a 1/4-inch opening. Once inside, rodents can cause structural damage with their gnawing; feed on, damage, and contaminate food and packaging; contribute to lost worker time and productivity; and increase extermination costs. Their adulteration of product can lead to FDA Warning Letters and repercussions, costly recalls from consumer complaints or foodborne illness outbreaks, and potential litigation, harm to your reputation, and lost business.

Rodents also will tear up product, cross contaminate packaging, nest in equipment, chew wires causing equipment shut-downs, and get into finished product, said Collins Pest Management President Dan Collins. “If you ship mice, you’re going to lose business.”

The greatest misunderstanding that food plants have of rodents, Collins said, is realizing the extent of their populations. “The number one thing people do is underestimate the rodent,” he said. Too often, a few traps are put out around the plant, a few mice caught, and the problem is thought to be solved. But no consideration or inspection was made of pallets, sub-slabs, or other areas that the mice may harbor ... and breed. “Because of this, the infestation gets completely out of control and becomes overwhelming,” he said. “In a food facility, one mouse is too many.”

In 24 hours, one mouse can urinate thousands of times and produce up to 75 droppings, said GMT Director of Marketing Drew McFadden. “Imagine if you have a serious infestation.”

Rodent Facts
  • Rats contaminate and destroy enough food worldwide each year to feed 200 million people.
  • Rodents consume or contaminate about 20% of the world’s food supply.
  • They have been reported to harbor and spread as many as 200 human pathogens, including those associated with salmonellosis, murine typhus, infectious jaundice, Weil’s disease, rat-bite fever, and Hantavirus.
  • As many as 14,000 people each year in the U.S. are bitten by rats.
  • House mice constantly give off micro-droplets of urine as they travel around their territory.
  • A female house mouse can birth up to a dozen babies every three weeks—as many as 150 a year.

Source: National Pest Management Association

Because of this, said GMT Vice President of Sales Dave Colbert, “If you have a rodent problem, you have to go box by box and product by product to make sure there are none in there.” Not only will the product need to be held and/or quarantined while an inspection is undertaken, but the costs in time and lost productivity for those conducting the inspection can be high.

“This doesn’t get solved in 24 hours,” he said, “rodents are intelligent creatures. They have been on Earth much longer than we have, and they’ve learned to adapt.”

Rodent Prevention

It is estimated that there are approximately 1.25 billion rats in the U.S., and the house mouse is said to be the most common mammal in the world. “Given those numbers and the fact that they are largely commensal animals, it means that food-related businesses having an issue with rodents is a when, not an if, proposition,” McFadden said. And when an issue occurs, it can carry significant expense. “With that in mind, it makes the most sense financially and otherwise to take steps to prevent rather than react to an infestation,” McFadden said.

“The only real long-term solution is being proactive,” he said. For food processors, this includes eliminating or reducing populations outside the facility and implementing exclusion practices to lessen the potential of rodents coming in or infesting products and supplies.

Solving problems through exclusion, which McFadden sees as more important today than ever before, should include such methods as the installation of rodent-resistant door sweeps that cannot be gnawed through; filling of cracks and crevices with fill fabric that cannot be gnawed and won’t rust or degrade; and sealing gaps in dock levelers making them impenetrable to rodents and other pests.

Much of it comes down to common sense, he said. “If you have a brick wall and you’re missing bricks, you’d replace the bricks.” Following that same strategy for any gaps or cracks in the structure will go a long way toward excluding rodents.

Rodent Management

Reducing exterior rodent populations also is key to keeping rats and mice out of the facility. One common strategy for reducing populations is the placement of rodent bait stations around the building and property. Collins follows this method, except that his technicians place non-toxic baits in the stations and monitor based on rodent pressure.

“If there is activity, we install snap traps and check them weekly until we have a period of no captures,” he said. Although this increases the amount of service needed, Collins sees it as a more proactive approach. Not only does it enable the calculation and trend analysis of rodent captures, it enables identification of impacted pests.

Collins has been using this approach at one facility for more than eight years, and plans to switch all Collins-serviced facilities by year end. “We feel we are catching on the outside more than on the inside with this method,” he said. Collins sees it as a more proactive approach, and, with a number of groups and states assessing the use of second-generation anticoagulants, he said, “I feel the industry will trend this way.”

The rodent management program is not just about placing traps, he added, but consists of five key steps:

  1. Identify the pest present.
  2. Determine source, extent, and severity of pest infestation.
  3. Identify conditions conducive or potentially conducive to pests.
  4. Implement best practices for pest management.
  5. Follow up.

Even when toxic baits are used in exterior rodent management programs, the manufacturers often recommend that non-toxic baits be used first as monitoring tools, and then the switch made to the toxic bait where rodents have been identified as frequenting. Some non-toxic baits contain a tracking “marker,” such as dyes or bioluminescence, which show up in fecal pellets and enable technicians to accurately identify the rodent, or other wildlife, consuming the bait, as well as its route of activity.

Implementing a preventive approach to rodent management means eliminating rodents outside before they can get in, follows the food industry’s trend away from reactive food safety toward proactive approaches, and incorporates the pest management industry’s trend of Integrated Pest Management (IPM) based on inspection, monitoring, and attaining data—then acting on it.


The author is Editor of QA magazine. She can be reached at llupo@gie.net.