We hate them and love them. Some of us feed them; others eat them.
Impossibly cute and incredibly wily, they can warm your heart - and chew up your attic. Squirrels are one of the top wildlife pest-control problems.
For Benson, a University of Pennsylvania assistant professor who studies the history and sociology of science, the urbanization of the eastern gray squirrel is a case study of our evolving view of nature: something we have fought, fostered, and simply lived with.
"You can learn a lot about people's ideas, and how they've changed over time, because of squirrels," he said.
They are so ubiquitous that it's hard to imagine cities without them. But in researching a vast array of old records for an article published last month in the Journal of American History, Benson found that by the mid-19th century, cities no longer had squirrels, partly because they offered no habitat.
In the surrounding countryside, squirrels were so numerous they were viewed as agricultural pests. In Pennsylvania, bounties were paid on 640,000 squirrels in 1749 alone, according to the state Game Commission.
The only urban gray squirrels were pets, which are illegal now. Consider Mungo, a girl's pet that Benjamin Franklin eulogized in 1772. The little guy had survived a transatlantic journey to England, but later escaped from its cage and was killed by a dog.
Lamenting Mungo's fate, Franklin wrote, "Learn hence, ye who blindly wish more Liberty, Whether Subjects, Sons, Squirrels or Daughters . . . "
"I read it as a warning," said Benson. A caution that freedom also brings more risks.
"It's a lot to put on a squirrel," Benson added, but he's convinced that that was Franklin's intent.
So Franklin might have appreciated the fact that Philadelphia is where the nation's urbanization of squirrels began, with their introduction into Franklin Square, now at the foot of the Ben Franklin Bridge. Other cities soon followed, from New York to Boston.
Decades later in New Jersey, when squirrels were scarce because the forests had been logged, officials imported some from Virginia and released them on the grounds of the Capitol in Trenton, said wildlife biologist Andrew Burnett of the state Division of Fish and Wildlife.
Introducing squirrels to cities was meant to transform the few green spaces from mustering grounds or cow pastures to oases of nature. Squirrels were seen as exotic creatures of the deep woods.
Soon, they were so tame that they were eating cakes out of children's hands.
As the squirrels proliferated, people began to wonder about the consequences. In the 1860s, a Pennsylvania Horticultural Society committee concluded that squirrels were a threat to birds, valued because they ate insects.
But not for long. They were just too popular.
Later, introductions were tied to the notion that nature in the city was essential for people's health and sanity.
Squirrels also became an ethics lesson. The tiny creatures' "readiness to trust" and ability to flourish "seemed to make them living proof of the reward of extending charity and community beyond the bounds of humanity," Benson wrote in the study.
The fact that they sat on their haunches and held their forepaws in front of them like little beseeching hands didn't hurt, either.
The cofounder of the Boy Scouts even talked of introducing "missionary squirrels" to cities to curb boys of a tendency toward cruelty, Benson found.
But squirrels will be squirrels. Eventually people didn't like their destroying flower beds and scratching in the eaves. Coincidentally, by the 1920s and 1930s, ecologists argued for a more natural view of nature. That meant no feeding. The squirrels were on their own.
When Benson embarked on his project, he had studied orcas, grizzlies, and other large, charismatic species. But those are often seen distantly through the lens of a TV camera. We encounter squirrels - for better or worse - up close and personal.
Today, we still hunt squirrels. Although the numbers have dropped in recent years - officials don't know why - hunters in Pennsylvania and New Jersey killed more than 180,000 last year.
They're seen as a way to interest youths in hunting. Unlike deer, "where you could go out and sit forever and just get cold, with squirrel hunting you can take a young hunter to any game lands and sit down for 15 minutes and have action," said Pennsylvania Game Commission spokesman Travis Lau.
Back in the cities, squirrels continue to adapt. And cause problems.
Besides bats, squirrels are the leading wildlife pest in this region, said Terri Seitz, co-owner of Seitz Wildlife Services of Drexel Hill.
The buggers destroy insulation, chew wires, and fall down fireplaces. Excluding them can cost $350 to $500, she said.
Likewise, most of the squirrel calls coming into the wildlife rehab clinic at the Schuylkill Center for Environmental Education in Roxborough are complaints. People want to know how to keep the little thieves away from their bird feeders or out of their attics.
The flip side is the people who want to save them after they have been hit by cars or the tree with their nest has been cut down.
Of the 3,300 critters taken to the clinic each year, 500 are squirrels. Only American robins outnumber them, said Rick Schubert, director of wildlife rehabilitation.
Benson never found details about that seminal 1847 release of squirrels in Franklin Square. But today, their kin sit on the benches, scamper through the miniature golf course, and scrounge in the trash cans. (They're partial to french fries.)
"They're residents of the park," said park director John Wilson. "They live here." And whatever's going on, "they're involved."
At Halloween, they chew out the innards of pumpkins to make little homes. Last Easter, an astonished Wilson took a photo as one snatched up an egg put out for the hunt.