Natural History, Wildlife Knotgrass Moth Caterpillar Image 22 September 2014 Ian Alexander Knotgrass Moth Caterpillar, Acronicta rumicis, in garden, on a beautiful autumn day. It has eaten a substantial portion of the leaf. Its aposematic black-red-white coloration and bristling setae advertise it conspicuously as foul-tasting or poisonous.