The corn earworm, Helioverpa zea, is the larva, or caterpillar, of a moth. There is almost always only one per ear, and they inhabit the tip of the ear, feeding on the kernels. I have seen a lot of people at the local farmers' market rejecting ears of otherwise excellent corn because there's a worm. What a waste! Organic corn often has a worm, because spraying with toxic insecticides is the only way to prevent them. All you need to do is cut off the tip of the ear, removing the worm and the damaged kernels, and you'll be fine. I'd much rather eat an ear of corn that had a worm removed than one soaked with insecticides.