Whether they’re scurrying across the subway tracks or running through pipes and sewers, rats and their furry counterparts are part and parcel of life in most major cities. There is no official number of the amount of rats that call the Big Apple home, but it is no marvel spotting rats anywhere and everywhere in the city. A PhD candidate at Fordham University has developed a particular interest in understanding the genealogy of these rats and produced a study that looks at the genetic distinction between New York City’s rats based on geographical dwelling, in an attempt to aid the city in dealing with its rat population.

Along with a team of undergraduate students, Matthew Combs, the PhD candidate that carried out the study, went on a two-year rat adventure across Manhattan, surveying every rat he could get his hands on. In tandem with the New York City Department of Parks and Recreation, Combs and his team were granted access to survey brown rats, also known as Rattus norvegicus, across the city’s parks and green spaces. For his study, Combs used a total of 262 samples of the rats that were captured, some of which were stuffed and given to the Yale University Peabody Museum of Natural History.

His personal fascination with rats aside, Combs’ study was threefold in its analysis; looking at the sub-species that developed based on where the rats lived in the city, where the rats originally came from and similarity among the city’s rats. What Combs and his team found is that New York’s rats, which most likely came from Great Britain on pilgrim ships to Ellis Island in the 1800s, were more similar to one another when they dwelt less than 200 meters away from each other. Additionally, what surprised Combs’ team was that there are two distinguishable subspecies of rats that are ‘native’ to Manhattan.

Among the brown rodents that were surveyed, Combs’ team was able to differentiate between Upper Manhattan rats and Lower Manhattan rats. The two types of rats are geographically separated by mid-town Manhattan, and differ based on the kind of trash and shelters where they dwell. Rats usually live their whole lives within a couple of blocks, which explains the geographical range (~200 meters) that Combs defined for his study. Despite being a buffer between the two subspecies of city rats, midtown Manhattan is not exempt from hosting a rat population but just lacks the kind of trash and shelters that the city’s rats are more commonly found around.

In a city where the rat population is estimated to be anywhere between 250,000 and well into the millions, Combs and his team could not depend solely on coincidental sightings to carry out their research. Through a crowdsourcing rat map, the team was able to encourage the public to record rat sightings in an effort to delineate areas the rats lived in the most. Combs’ team scoured rat holes and looked for rat droppings, chew markings, and sebum – the grease trail rats leave behind near places they frequent. The team used a mix of peanut butter, bacon and oats to attract the rats before catching them. 

Combs’ research, which he his using for his dissertation on rat ecology in New York City, is being used by the city’s municipality to commission a $32 million campaign to fight the city’s rats. According to Reuters, New York’s mayor, Bill de Blasio, said in an official statement that he “refuse[s] to accept rats as a normal part of living in New York City.” The mayor’s campaign, which will target the Bronx, Manhattan and Brooklyn, is expected to reduce New York City’s rat population by 70% by the end of 2018. Fortunately, the city’s authority does not plan on exterminating the rodents as a solution to the scores of rats scurrying above and below the city but, rather, intends to improve infrastructure to deprive them from feeding and, in turn, reproducing.

Far from just being pestilent, urban wildlife can help planners and researchers understand more about health and wellbeing in cities. Last year, a team of researchers used pigeons in New York City as bioindicators in a study, to understand how lead pollution affects children’s well-being in the Big Apple.