Ragged holes in the leaves and bits of green excrement are signs of imported cabbage worms. The female butterfly zips about from plant to plant, depositing her eggs at the base of the leaves. In about a week, tiny green caterpillars hatch and begin to chomp the leaves. Larvae eventually bore their way into the main head of the vegetable, turning it into mush. When cabbage plants are small, cabbageworms feed primarily on the undersides of the developing leaves. When the heads develop, cabbageworms feed on the outer leaves and bore into the centers. Larvae also cause damage by contaminating the heads with their greenish-brown excrement.