If you live in North America, you probably recognize European starlings, those little black birds with white polka dots that chirp and chatter and, in the winter, hang out in flocks of thousands. There are 200 million of these birds on the continent, and they can be found as far north as Alaska and as far south as Mexico. Numerous though they are, starlings are actually non-native invasive species. And we can blame Shakespeare for their arrival in America.

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Steven Marche explains in How Shakespeare Changed Everything:

On March 6, 1890, a New York pharmaceutical manufacturer name Eugene Schieffelin brought natural disaster into the heart of completely without meaning to. Through the morning snow, which congealed at times to sleet, sixty starlings, imported at great expense from Europe, accompanied Schieffelin on the ride from his country house into Central Park—the noisy, dirty fulfillment of his plan to introduce every bird mentioned by Shakespeare into North America. Schieffelin loved Shakespeare and he loved birds….The American Acclimatization Society, to which he belonged, had released other avian species found in Shakespeare—the nightingales and skylarks more commonly mentioned in his plays and poems—but none had survived. There was no reason to believe that starlings would fare any better. Schieffelin opened the cages and released the birds into the new world, without the smallest notion of what he was unleashing.

For someone who apparently loved birds, you have to admit this was a pretty daft plan. There was every reason to believe that the birds would die—it was bitterly cold and sleeting, and attempts with other species had led to dead birds. But the tiny flock found shelter beneath the eaves of the American Museum of Natural History, just to the west of the park, and they survived the winter. And then they began to breed, and spread, and breed some more.

It seems that the starlings some special characteristics that gave them an advantage over other bird species, Marche writes:

The protractor muscles of their beaks allow them to pry and to probe better than other birds. They can open their bills after pushing them into the soil, which allows them to forage for invertebrates easily and in drier areas. The starling’s eye have evolved to the narrow front of its face, giving it the perfect view for prying. Its binocular vision combined with its open-bill probing ability means that starlings can find insects in colder climates better than other birds, which means that starlings do not have to migrate to warmer climates in winter, which means that they can take the best nesting holes during the breeding season.

Starlings will bully other birds, kicking bluebirds, flickers and woodpeckers out of their nests. They can consume whole fields of wheat and transmit avian, animal and human diseases. A fungus called Histoplasma capsulatum can grow in the soil beneath roosting starlings; the fungal spores can become airborne if the soil is disturbed and cause the disease histoplasmosis, which, in rare cases, can cause blindness or death.

People quickly realized what a pest these birds could be and tried to get rid of them. In Hartford, Connecticut, in 1914, residents tried to scare the birds away from their nests by fastening teddy bears to those trees and firing rockets through the branches. The White House tried speakers that emitted owl calls. Columns around the U.S. Capitol were outfitted with electrified wires. People have tried shooting, poisoning, trapping, repelling and frightening the birds, but the population still grows. They have plenty to eat and lots of habitat to live on—what else does a species need?

These birds are a prime example of why it can be so difficult to control an invasive species once it has become established—no matter how many you wipe out, there’s still plenty to take their place.