Vertebrate Pests

There’s been a lot of attention on rats and the Big Apple (and other cities) this past spring. Specifically, the topic of rats in the city’s restaurants has made big news. First, a family of rats foraging on the floor of a fast food eatery was shown on national television and all over the Internet. A few weeks later, the TV show Inside Edition filmed rodents in several more New York restaurants (see next month’s column: “Restaurant rodent control”). All of this attention once again has prompted two perennial questions: Why does New York City seem to have so many rats? And is New York the largest “Ratopolis” in the world?

The lay public and the lay media seem to think these questions should have simple answers. Hardly. Rat populations in mega metropolises the likes of New York are a complex issue. First of all, no data exists that scientifically compares the rat populations of New York City to other metropolises such as Washington, D.C., Boston, St. Louis and Chicago, or on a global scale, to cities such as Buenos Aires, London, Paris and so on.

Besides, the rat populations of our cities cannot be stated in such simple statistics as “the city with the most rats.” And if such a measurement could be done, the more salient statistic of course would be the number of rats per capita. But, no one knows this statistic either and it’s a safe bet to say we will never know. Rats don’t exactly fill out official Census Bureau forms.

Does New York City contain a large population of rats? Yup. Are there millions of rats? Probably. But is there one rat for every one of the 8 to 12 million New Yorkers? Highly unlikely (similar to the rats, no one is sure of the actual number of humans currently living in NYC either). Typical of city rat infestations, some neighborhoods perhaps contain several rats per person while in other neighborhoods there are zero rats per person.

But, yes, in general terms, New York is surely one of the world’s greatest metropolises and also one of the greatest Ratopolises. But why? What accounts for the rat’s love affair with the Big Apple? I’ve been working intensely with rats and rat infestations in New York for the past four years now, and I ran a pest control route that included New York City for three years full time. I’d like to offer at least some insight into the rats of New York. Other factors beyond what I’ll mention here are of course at play, and no doubt, there are even some factors that are unknown and thus unmeasurable to us at the present.

New York is an old seaport city established in 1625. At that time, it was already a bustling trade harbor receiving ships from the cities of Europe and even further east towards Asia. It is believed the Norway rat arrived on American shores from these regions some time in the mid to late 1700s. Thus, the rat has had at least 200 years to become established, multiply, and learn all the nooks and crannies in which to feed, hide and thrive in the city. By the early 1800s, the rat was well established in New York.

RAPID GROWTH AND RENOVATIONS. Lines of streets began connecting to other lines of streets (such linear pathways with food and harborage are ideal for rodent dispersal). Until the arrival of the car in the 1900s, these streets contained hundreds and hundreds of horses and, of course, horse manure, as well as associated hays and grains. Eventually, sewer pipes were installed below-ground, providing rats with protected subterranean highways and harborage sites.

Over 100 years of rapid growth, New York had to meet the infrastructural demands of an exploding human population: more sewers, steam and water tunnels, subways, parks, refuse collection sites, highways, streets and seaports; in some ways these were all piled one atop of the other. In fact, New York contains one of the largest agglomerations of city infrastructures found anywhere on earth. Because many systems are subterranean, they are exploited by the geotropic-negative brown rat for harborage and/or dispersal highways.

Growing rat populations require a fair amount of nutrition as well as protected places to hide from predators and successfully rear the young. Part of the reality of a large, densely populated city of 8 to 12 million residents is that millions of fragmented foods (food shrapnel) and food residues occur on a daily basis even in the presence of well-coordinated sanitation programs involving trash collection and street sweepers. Consider that litter experts estimate about 25 percent of a population litters on a daily basis. If you walk down some of New York’s busiest streets in the afternoon, it is common to find a wide range of food shrapnel that offers foraging rats a nutritional balance.

But it’s not as simple as sweeping streets or keeping trash in cans (so often the lay person’s solution to this complex situation). For example, in addition to the discarded food scraps and refuse containers, New York rats have at least another dozen opportunities in which to feed. From within each street’s corner-storm basin (145,000 of them) to sewers and subways, rats have plenty of options that also include grease films, flotsam and aquatic animals along the shorelines, pet feces, outdoor pet and pigeon feed, pigeons, cockroaches and more.

With so many foods and feeding opportunities, should one source of food temporarily disappear (e.g., the food trash bags get picked up), the rat can easily shift to another source. Additionally (and importantly), rats readily collect foods in excess of their needs and carry them back to their nests or to various cache nooks in their territories where the food can be eaten by them, or by other members of the colony some time later should the local food become temporarily unavailable. Research on the rat’s caching behavior has shown rats can store up to a week’s food supply (or more) in this manner.

From this aspect, alone, it is questionable whether or not it is realistically possible to limit food in a city the size, scope and intensity of New York to the level that would suppress rat populations to levels low enough to be acceptable to New Yorkers.

In addition to an abundance of foods and food sources, there is also an abundance of harborages available to the New York rat. Without listing all of them, a few of the more common harborages include: (1) ground earthen burrows (beneath bushes in parks, along building perimeters in the landscaping, in tree pits, along ditch banks, highway embankments, beneath the curbs and sidewalks within the earthen fill); (2) within exterior and interior structural voids of all kinds; (3) within old sewer systems and other tunnel-oriented infrastructures (nearby water and steam lines, electrical chases, telecommunications, etc.); (4) within the protected zones of subway platforms and track tunnels; (5) within and/or beneath junk, discarded furniture, abandoned cars, etc.

So, even based on just this partial profile of the New York rat, it is easy to see why the rat “loves” New York City, and how it can breed and breed and breed.

THE FUTURE. Will we ever achieve a higher level of rat management in New York and similar metropolises? When you ask the lay public this question, many think the answer lies in future scientific developments that will result in better traps or poisons. But in those urban areas where the rat is thriving, it actually has very little to do with traps and baits.

The answer is both simple and complex at the same time. Homo sapiens (meaning wise man) could be far wiser by taking a lesson from many of the lower mammals and animals: that is, keeping its own nest cleaner, and like the ants, do a better job at working together despite all “the fences.” This just doesn’t mean with the neighbor next door but across national, state and city agency fences as well. But for sure the most important aspect must occur at the individual level first, and the municipal level second. In a high-density city like New York, only a small percentage of 10 million residents who foul the nest is a lot of food and harborage for rodents (and flies and cockroaches, pigeons, etc.). And therein lies the complexity and the frustration.

Nature is full of examples of one animal benefiting from the “leftovers,” wastes, and evacuated or abandoned harborages of another (e.g., jackals feeding on what’s left from the lion; ants feeding below on the dropped foods of the birds above, gulls following a fishing boat for discarded fish entrails, the rabbit occupying the abandoned woodchuck den, the yellowjacket nest in the evacuated chipmunk burrow and so on).

In other words, ecologically speaking, where you find one animal, there is often a list of associated commensal and parasitic animals that “follow.” So too for city rodents and city people. They all are co-existing city dwellers. And, of course, this is not just in New York but in most large-scale urban human habitations the world over.

John McLoughlin in his 1976 urban inquilines book, “The Animals Among Us,” provides one of the best summary statements on the relationship between the city rat and urbanites: “All the ingenious traps, all the virulent poisons, all the cunning predators domesticated by offended humanity have served to cause only momentary fluctuations in localized populations of rats. The world rat population rises in direct proportion to the world’s human population, and neither species shows any sign of faltering.”

The author is president of RMC Consulting, Richmond, Ind., and can be reached via e-mail at rcorrigan@giemedia.com.