Abstract.1. Collards (Brassica oleracea L.) grown in clumps were more difficult for unstarved, early instar cabbage white caterpillars (Pieris rapae L.) to find than collards spaced at regular intervals, although total plant densities were identical.2. Early instar, unstarved larvae are less mobile than later instar larvae (our data) or starved larvae (Jones' 1977 data).3. Starved larvae and late instar larvae tend to find plants more readily than do unstarved or younger larvae.4. We contend that larval mobility governs the success of searching caterpillars and their sensitivity to variations in plant dispersion.5. Our results show that the dispersion of targets can influence searching success even though target density is constant. This means that the degree of clumping in host plants is capable of influencing their availability to herbivores.