Black mustard, Brassica nigra (L.) Koch, is a wild annual species found throughout Europe and fed on by larvae of the large cabbage-white butterfly, Pieris brassicae L. We examined the impact of herbivory from P. brassicae, a gregarious herbivore, on B. nigra grown from wild seed collected locally. In greenhouse studies, the response of B. nigra to four herbivore densities in two developmental stages of the plant was quantified by measuring leaf damage, plant height, days to flowering, silique number, and seed production. Pieris brassicae readily attacked B. nigra leaves, although the timing of the attack did not affect seed production; attacked plants produced as many seeds as as nonattacked plants. Plant height was affected when plants were attacked early, but not later, in development, suggesting a connection between their belowground zone of influence and ability to regain biomass. These results demonstrate that at the herbivore densities and timing of damage studied, B. nigra tolerates folivory from Pieris brassicae through compensation.