Robins and Earthworms - 自然英语

Arobin tugging an earthworm from the ground is a symbol of spring. But that wormit’s eating hasn’t always been here.Whenglaciers pushed south into what is now the U.S. around 20,000 years ago, theyscraped off the soil layer and spelled the end of native earthworms except inthe southern states. So that earthworm plucked by the robin is probably arelatively new arrival, most likely a species Europeans conveyed to theAmericas in plant soil or in the ballast of ships.Soif not earthworms, wh...