Farmers often use poisonous chemicals known as pesticides to kill off insects that feed on their crops. But an ancient, less toxic technique is making a comeback - sending in ducks. Farmers take their flocks of ducks into the fields each day until harvest time. The ducks feast on pests and devour weeds that would otherwise choke the crops. As the ducks wander through the field, they stir up the soil, releasing nutrients that feed the crops. Rice farmers in Asian countries have been using ducks in this way for hundreds of years.