The employees, all goats, arrived on Wednesday to do what they do best: eat the invasive plant species—things like kudzu, poison ivy, and English ivy—that are putting the cemetery's trees and gravestones at risk. (Learn more about the mountain goat.)

"These invasive plant species strangle and kill our trees," said Paul Williams, president of the 206-year-old cemetery. "The trees then fall into the cemetery and topple our headstones."

So for the next week, the cemetery—which houses the likes of J. Edgar Hoover and John Philip Sousa, among others—is renting a herd of eco-goats from a farm in southern Maryland. The goats will work round-the-clock to clear everything up to seven feet high, said Daniel Holcombe, the grounds and conservation manager