In 1856, the New York newspaper Daily Times reported on an "unusual visitor" to a downtown tree: a squirrel. It was probably an escaped pet, and its capering exploits apparently drew a crowd of hundreds that had to be dispersed by the police. Yeah, we're finding it hard to believe too. But apparently, the sight of that little bushy tail was enough to send New Yorkers into a tizzy. If any of those passersby had happened to be from Philadelphia, they might have thought that the critter was old news. The City of Brotherly Love had already introduced three squirrels into its ecosystem some 10 years earlier, installed in little houses at Franklin Square. Still, squirrels wouldn't become a common sight in American cities until a psychological shift changed the way the country saw the creatures.

People might have thought squirrels were cute enough to keep as pets or captive exhibits in previous years, but as they became more a part of the urban landscape, our relationship with them changed. Soon enough, squirrels installed in parks as public entertainment were being fed so often that they grew too fat to climb trees. But to the influential city planner Frederick Law Olmsted, keeping squirrels in cities was a matter of ideological principle. Having squirrels around, in his view, gave the urban population a direct connection to nature that would prove beneficial to their physical and mental health. Even Boy Scouts co-founder Ernest Thompson Seton prescribed feeding the squirrels to help quell boys' more violent urges.

As it happened, squirrels spread across the continents' major cities in fits and starts. But although other parks may have gotten on the bandwagon sooner, perhaps no place exemplifies the changing relationship of man and squirrel than Central Park.

There were squirrels in Manhattan before there was a city there, but by the mid-1800s, their population was practically nonexistent. Then in 1877, about 20 years after the first bushy-tailed rodent found its way into the newspaper, the city decided to capitalize on squirrels' growing fandom by bringing them back to Central Park. They planted squirrel-friendly nut trees and installed cozy squirrel homes, then released a handful of chipper gray squirrels to run wild in the park. The following year, they released 30 more pairs. By 1883, the park was home to at least 1,500 of them.

In the late 19th and early 20th centuries, the care of squirrels was viewed almost as a moral imperative for New Yorkers. Some opinion columns might equate feeding squirrels with helping the homeless, while others took a more antagonistic view. But whether they belonged there or not, the city proved to be a perfect place for the arboreal fuzzballs to live. As populations swelled, the idyllic view of squirrels as a window to the natural world made way for a grimmer, more realist view of ecosystems: Sure, squirrels were an important part of the food chain, but so were the hawks and falcons that fed on them.

These days, it's fair to say that squirrel fever has died down a bit. We're guessing they won't make it into the newspaper again, but they're still a nice reminder of the natural world. And maybe next time you see a squirrel, you'll take a moment to watch its adventures — after all, that's what it's there for.

Get stories like this one in your inbox or your headphones: sign up for our daily email and subscribe to the Curiosity Daily podcast.

Urban parks and the squirrels that dwell there did more than add some greenery to the city. They shaped the American psyche. In "Genius of Place: The Life of Frederick Law Olmstead" (free with a trial membership to Audible), Justin Martin sees how the man who brought squirrels to the city also instigated social reform. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.