Is it easy to be a herbivore when it comes to finding food? Since there is so much green vegetation around it is hard to imagine that herbivores, which include such diverse creatures as sheep and caterpillars, face particularly difficult challenges. Yet, the world is not always a green place - especially in the winter, plus, a lot of available vegetation is nutritionally poor and incomplete in terms of specific vitamins (which is why human vegetarians must work hard to meet their diet needs). Also, many plants are armed with thorns and spines, and defend themselves against being eaten. Other plants are less obviously protected - they produce toxic chemicals which may have both lethal and sub-lethal effects. Plant-herbivore interactions are highly dynamic, and many herbivores are adapted to learn very quickly how to detect the best food. This talk explores how this learning process works, the impact of herbivores on plants and the ways in which the plants fight back!