National science standards require an understanding of animal behavior, diversity, and adaptations of organisms, as well as the concept of science as inquiry. We have developed a hands-on classroom activity that addresses these standards through teaching about herbivory and diet breadth, using locally abundant caterpillars and plants. This activity provides students with opportunities for careful observation, data collection and analysis, and development of testable hypotheses for further experimentation. The lesson can be adapted to different grade levels, with students taking on varied levels of responsibility for formulation of hypotheses, experimental design, data collection, and data analysis.