[Rodent Control] 18 City Rat Myths & Half-Truths

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August 10, 2004

Over the years, many press releases and various popular magazines and movies have featured stories about rats in our cities. In this age of information technology, good information can be transferred quickly. On the other hand, the Internet, poorly researched newspaper articles, and misinformed municipal employees and pest professionals can all serve to quickly misinform and disinform the public about city rodents and their control.

The following are 18 myths, misconceptions or half-truths commonly heard when talking to city dwellers about the rats in their neighborhoods.

a norway rat by any name

In cities, Norway rats, depending on where they are infesting an area, may be called "sewer rats," wharf rats, river rats, alley rats, house rats and barn rats. Some people mistakenly believe there are different "varieties" of rats according to these names. Roof rats may also be subject to similar misunderstandings.

one...two...nine...rats per person

No one knows how many rats per capita exist in any city. It probably ranges from zero rats to several dozen rats per person in any area of a city. It is only safe to say we know there may be dozens or millions of rats in any one city, depending on many urban environmental factors.

rodents have collapsible skeletons

Of course not. If a rat or mouse can get its skull through a crevice or a hole, the rest of the skeleton is flexible enough to accommodate the rodent gaining entry.

rats must gnaw on wood, wires or cables or their teeth will continue to grow

This is not true. Rats maintain incisor growth and sharpness by grinding the lower incisors against the uppers. They do not need to gnaw on objects, although they will supplement tooth grinding with object gnawing. Gnawing on objects provides the rodent with one form of a foraging strategy.

super sewer and alleyway rats as big as alley cats

The Norway rats that inhabit sewers are not necessarily any larger or "super" than their cohorts inhabiting an alleyway or park bush above ground. In fact, they could just as easily be smaller. In extensive studies of the sewer rats of London, the heaviest rat captured weighed 15oz/410g, which is an average "large" adult Norway rat. But larger rats have been recorded in and around farms and other environments. Thus far, the heaviest Norway rats reported in the literature are rats ranging in weights of 1.3-1.8 pounds.

city rats have become "immune" to rat poisons

It is true that many rats and mice are now resistant to the first-generation anticoagulant rodenticides. But luckily so far most rats in U.S. cities are still quite vulnerable to the second-generation compounds. (However, the "resistance horizon" needs to be carefully monitored.)

mother rats teach their babies to avoid traps and poisons

Young rodents often do learn which objects and food items may be acceptable by following their mother around just after or close to being weaned. If the mother rat bypasses a trap or bait, a young rat may also bypass these items when it is out foraging about on its own at a later time. But the mother rat likely passed the baited traps or baits due to more attractive resources further along or because she is fearful of any new objects (she might just as well pass by a child’s toy containing smudges of peanut butter).

cats control city apartment mice and young rats

Cats (and dogs) may kill the occasional young or old rodent, but they do not control rodent infestations.

city rats are aggressive and attack children, dogs and the elderly

Some rats, if provoked and cornered, will fight their way out of the confrontation, as will many wild animals. But most rats do not outwardly attack humans.

Babies, bed-confined elders, and the homeless sleeping in doorways and alleys, however, are occasionally bitten by unprovoked rats. Most likely these individuals fall asleep with food residues on their hands or faces, and foraging rats attempt to lick or chew the food residues off of the sleeping individual. If left unopposed, some rats may consume a considerable amount of human flesh, causing serious wounds. Conservative estimates place as many as 14,000 people each year in the United States bitten by rats. This figure is likely to be substantially lower than the number of actual cases as most rat bites remain unreported.

"rat cities" exist beneath human cities

Some people believe legions of rats exist in a city’s sewer system below ground. It isn’t certain any rats are living in a particular sewer. Just as it isn’t certain a particular restaurant has none, a few, or thousands of cockroaches hiding in the cabinets and walls.

the rats of the sewers have mutated into blind and unusually large rats

The Norway rats that infest sewers are neither blind nor unusually large.

rats and mice do not have urine bladders and/or they cannot control their sphincter muscles; thus they are constantly defecating

Mice and rats do urinate and defecate relatively often compared to some larger mammals. But they do have bladders and their sphincter muscles are not out of control.

street jackhammers cause rats to flee the sewers to nearby ground buildings

Not true. Rats are, for the most part, unperturbed by above-ground street construction practices. In fact, they will not leave a suitable sewer system or subterranean harborage even if their sewer is under construction unless their burrows are directly excavated.

rats transmit rabies

The Norway rat or house mouse is not considered an important reservoir for the rabies virus in the U.S. Rat bites do not necessitate the victim being treated for rabies as is commonly done for bat, fox, raccoon, dog, cat and other wild animal bites.

the rat in the alleyway is a serious health threat

No telling. In most cases, the average city rat or mouse is not carrying any major serious pathogens. However, from time to time, rats and mice do transmit diseases to humans. Thus, it is the potential of possible disease transmission that we as a society must protect against. In other words, it pays to err on the side of safety relative to rodents and diseases, and implement quality rodent control programs.

rats are vectors of hantavirus pulmonary syndrome

The Norway rat has been implicated with various strains of hantavirus, but not the most lethal pulmonary strain (e.g., the sin nombre hantavirus) that attacks the respiratory system. Hantavirus pulmonary syndrome is most associated with the deer mouse, white-footed mouse and several other wild rodents. Nor is the house mouse associated with any highly lethal forms of hantavirus.

mild winters are causing rat explosions

Many factors contribute toward the peaks and valleys of rodent populations in our cities. Some of these include increases in construction, local refuse management practices, higher human population densities, urban sprawl, mild winters and the overall aging of many of our nation’s city’s infrastructures.

we will never be able to get rid of all of the rats in our cities

This is probably true. But if humans would get organized on their rat management programs, allocate the right amount of monies and resources toward rat abatement, and each and every person treat his or her urban environment with a commitment to "leaving it cleaner than you found it," we could perhaps put Rattus norvegicus on the "rarely seen" list of urban wildlife.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@giemedia.com or 765/939-2829. To order a copy of his book Rodent Control, visit www.pctonline.com/store or call 800/456-0707.