[Rodent Control] Urban Legends

"…And mice and rats, in spite of cats, gaily skip about…" — from a Costar Exterminating newspaper ad, New York City and Philadelphia, 1855.

Among the lay public in our cities, where rats and mice are common, the question, "Why not get a cat to control the rodents?" persists. We hear this question posed repeatedly from apartment dwellers and building superintendents, as well as private homeowners in suburban developments.

Society has been conditioned towards the idea that cats are effective rodent predators. Consider that most of us have actually witnessed a cat pouncing upon a live mouse; or we’ve found a dead, wet mouse in a house containing a cat. Many city people can attest to having seen an alley cat carrying off a "big-ole rat." Cat lovers proudly claim how cats help control mice. Cat enthusiasts who support the care of free-roaming cats in city parks often state "they help control rats and mice" as the main justification for promoting the care of park cats.

And, some of the earliest TV cartoon plots (Disney and others) have depicted cat and mouse scenarios where a cat is seen chasing a frightened rodent. Consequently, from our toddler days, most of us have been imprinted with the image of cats being natural enemies of rats and mice. Finally, even in the earliest cultures dating back to the Egyptians, there are drawings and records telling the story as to how cats were used in storage facilities to protect the grain from rodent attack.

So there is plenty of information to at least support a perception that a cat helps control city rodents. But is this true? Do domesticated cats have any value whatsoever in controlling rats and mice around city apartments and buildings? And if so, to what extent?

The objective of this article is to examine this question from a scientific perspective.

PREDATORS IN THE WILD. In the wild, several animals are predacious upon field mice and rats. The more common ones include coyotes, foxes, wolves, feral dogs, feral cats, bobcats, raccoons, skunks, opossums, snakes, hawks and owls. All of these predators are driven to find prey for food. The simple plan for them, of course, is to find food or starve.

In certain natural environments, research has shown that feral cats can significantly impact rat and mouse populations. Newsome (1990) reports of a New Zealand forest in which cats effectively suppressed rats and mice. But it cannot be assumed that cats are effective predators on rodents in all wild environments. Begon et. al (1991) summarize much of the research on predator/prey relationships that demonstrate many cases where predators have no apparent impact on their prey’s population dynamics or abundance (e.g., owls and rodents).

So what happens when cats are domesticated within a city environment? Are they effective as domestic predators on domestic rodents?

CITY CATS. In the highly populated large cities of the United States (e.g., New York; Philadelphia; Washington, D.C.; Baltimore; Chicago; San Francisco; etc.), the role of cats as rodent predators changes dramatically. The primary reason for this is humans become direct and indirect providers for cats (and dogs). In fact, they become providers for rodents concurrently. Directly, people feed their pets. Indirectly, stray cats often utilize the same food discards and garbage that rats use.

Of course, dogs and cats are now companion animals to people in urban, suburban and rural areas. Surveys show the common house cat to be the No. 1 American house pet with about 63 to 65 million cats associated with households, while about 61 to 62 million dogs are maintained as pets.

But in cities, the relationship between cats and people varies widely. Some residents highly pamper and completely house their pets indoors. Some cats, for example, are maintained strictly as house cats. These cats are declawed, never allowed outside, and may enjoy pampering that exceeds even that placed upon a fellow human being living within the same structure. Other people provide only marginal care by only partially feeding and housing cats in their homes, yards and basements.

Some cats and dogs exist as "strays" in the cityscape. That is, they live independent of an owner and exist as opportunists in finding shelter and food. For stray cats in our large cities, finding shelter is not difficult. Alleys containing junk piles, stairwells, basements, abandoned cars, park bushes and even the engine blocks of daily-used cars are utilized by stray cats and dogs for harborage.

Stray cats and dogs also have little trouble locating food. During both day and night (often tied in with garbage removal schedules), cats and dogs forage as scavengers upon city streets and properties. Trash placed out on the curbs in cans and bags, for the most part, provides enough suitable food for not only stray cats and dogs, but of course for rodents and pigeons as well. In some cities, or at least in some specific neighborhoods of the city where it is common for food scraps from the lunches of pedestrians to be discarded into the street, cats, dogs, rodents and pigeons all thrive on chicken, hamburgers, rice, pork, grease, donuts and a wide assortment of other human food scraps. Moreover, in some city neighborhoods, it is not uncommon among a several-block radius to find people putting out cans of cat food each evening. Apparently, this behavior serves to help satisfy some people’s drive for nurturing.

CITY CATS AS CITY PREDATORS? In the big city environment, cats can best be described as opportunistic quasi-predators of rodents. In other words, as many people will attest, and research has shown, cats do kill the occasional rat and mouse. But in a modern-day city, a predatory event is dictated by the specific health and drive of the cat and the particular rodent prey occurring at a specific moment. Technically, should a cat kill the first pregnant mouse entering an apartment or a house, and none follow, the pet has prevented a possible infestation. But this cannot be interpreted as cats being effective at controlling established rodent infestations.

Early studies and observations on rats (e.g., Lantz 1910; Stewart 1946) noted that cats specifically are not effective in controlling rats. Southern (1954) states "...repeated observations have made it quite clear that large numbers of mice can survive successfully in spite of cats."

Childs (1986) reported that cats do take some rats in cities. However, there was a size-dependent selection of rats by cats, whereas cats will catch only juvenile or sub-adult rats and do not complete their chases of adult rats. He also observed "...although adult cats and large rats were frequently observed in close proximity, no aggressive behavior was directed by the cats towards the rats, and generally these species coexist peacefully in alleys."

In a study of Baltimore cats, Jackson (1951) found that cats did nothing more than catch rats that would eventually die from one cause or another, and that their predation had no impact on reducing the rodent population.

Cats maintained as true companion pets are simply too well fed and cared for to maintain a strong predatory drive. To this point, Childs (1986) also discusses other research that indicates "rat killing in cats is a trait that may depend on early experience and learning, and it is possible that in urban environments, where food resources are plentiful, few cats need to rely on rat predation. A large percentage of free-ranging cats in cities are known to have been owned at one time, and therefore may have had no early experience with rat-killing."

Additionally, house pets often contribute towards the likelihood of a rodent infestation because rodents are highly attracted to pet foods stored in garages, basements, pantries and cabinets. Similarly with dogs, there are countless cases of rats burrowing beneath exterior doghouses and feeding from the dog or cat’s dish while the pet is off elsewhere or is asleep at night.

RATS & CARS; MICE & CABINETS. An important reason cats are not effective in city rat control is because cats do not have many windows of opportunity where they can pounce upon savvy, breeding adult rats.

Around the exteriors and peripheries of city buildings, the abundance of harborages and hidey-holes that can be used by rats and mice greatly limits the effectiveness of any city predator, be it the meanest alley cat, a feisty junkyard dog, or a watchful hawk, owl or falcon. Rats can quickly escape predators by bolting beneath junk piles and bushes, darting down into holes that exist in the ground, curbs, building foundations or street catch basins. Or, easiest of all, rats need only scurry beneath the closest parked car. In fact, along many streets of New York, rats often travel the length of entire blocks beneath cars parked bumper to bumper. This situation allows the rat to escape detection of not only any cat, dog or bird predator, but also of its most realistic city predator — the human.

Inside apartments, homes, and garages, a myriad of readily accessible nooks and crannies exist for rodents — especially the mouse. Healthy mice can quickly escape the swiping paw of a well-fed cat by merely darting beneath a chair, the stove, refrigerator and so forth.

In fact, the typical house mouse inside an apartment, often does not even expose itself to a cat or human. In most situations, mice forage for food completely within kitchen cabinets and drawers. Or, they can find food up off the floor at night on counters, stovetops or around the sink. Or, food crumbs are easily found on the floor and in nooks and crannies between the stove and the cabinet, or in the spaces behind the refrigerator and the stove. All of these spaces are too small for even the most determined cat to fit. And should the mouse forage out onto the floor, it’s not far away from shelter. The mouse can cover about 12 feet per second, which enables a healthy mouse a good chance of darting to cover with the appearance of an oncoming cat or dog.

If you have ever tried to corner or mouse inside a room or area, you know how agile and wily this little mammal can be. The house mouse didn’t get to be the second most successful mammal on earth by being easy prey.

IS ODOR A DETERRENT? Will simply keeping a cat or dog around a home apartment or basement help keep rodents away? Many apartment dwellers believe they do. The premise is that the smell of a cat and dog as the rodent’s "natural predators" helps to deter them.

Testimonials to this point from apartment dwellers in large complexes who own cats are pervasive and ongoing. Many pest professionals who service multi-family housing complexes will readily attest to the fact that in some (but not all) buildings, those apartments with cats seem to have fewer rodent problems than their cat-absent neighbors.

But the science of prey and predator scent and the role they play under different conditions remains poorly studied. For sure, most of us know of the significance of scent among and between animals. Dogs and cats clearly show signs when they smell rodents and other animals in their areas. Dogs (mine included), upon smelling a rodent in the house, will excitedly "go on the hunt" around the house. And many young cats exhibit a characteristic "stalking," ready-alert posture when hearing, seeing or smelling a rodent nearby.

Prey species utilize and respond to scent as well. Some research indicates that cats and or cat scent may act as a deterrent to rodents entering a building. In studies by Elton (1953) of cats and rodents in farm environments and farm buildings (barns, corn storage sheds), cats were credited as helping to deter new mouse invasions from getting a food-hold and/or perhaps discouraging mice from occupying premises in which cats were actively patrolling.

In one study of rats inside a large city zoo, rats avoided foraging for food inside the cages of the big cats while the cats occupied those cages. When the big cats were removed, or the cages were converted to non-predator animals, the rats quickly resumed foraging about in those cages (Farhang-Azad, et al., 1979).

Whether or not apartment cats help to deter invading rats and mice in and around city structural environments is unknown. Perhaps, if mice in a particular apartment complex have easy access to alternative cat/dog-free apartments, they may avoid those apartments with the pet scent in the same manner the rats avoided the big cat cages in the zoo. But, if cat-free options are not readily available, what’s a starving rodent to do? Most likely, as in the wild, they will need to take their chances. Besides, many pest professionals will readily attest to treating for rodents in homes and apartments that have dogs and cats. In fact, this is one of the underlying reasons for the development of, and the utilization of, tamper-resistant bait stations in residential settings.

In all probability, the effect of cat and dog scent on urban rodent invasions and the development of infestations are likely to vary significantly depending on several factors beyond the obvious.

SUMMARY. Cats and dogs certainly provide us with companionship, which to some is itself enough reason to keep a pet. But it would be a poor decision to house and feed a cat for the purpose of helping to control rodents because they are not efficient in preying upon rats and mice to any level that will check their numbers relative to infestations in and around city buildings.

For those who enjoy the company of cats in city apartments, in some cases, it may be possible that the cat provides some additional benefit in helping to deter mice from entering from beneath the door or via some other hole when the rodent detects the odor of the predator.

Nevertheless, it still makes far more sense to spend the time and money that would be used on the cat to thoroughly rodent proof the home or apartment — which is neither difficult nor costly to do. Many city health departments and university Web sites provide guidance on rodent proofing.

At a minimum, all doors should contain pest brushes. All penetrations (heating, plumbing and gas lines) through floors, walls and ceilings should be properly sealed (steel or copper wool plugs are only temporary). Any gaps in floorboards leading to wall voids must be fixed.

In other words, any apartment dweller thinking of getting a "mouser" is better off reminding, and re-reminding, if necessary, their building superintendents and property owners of their responsibility to ensure the building is rodent-proofed from the basement up through each and every apartment.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@giemedia.com or 765/939-2829.

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