1. Deciphering the mechanisms that underpin dietary specialization and niche partitioning is crucial to understanding the maintenance of biodiversity. New world army ants live in species-rich assemblages throughout the Neotropics and are voracious predators of other arthropods. They are therefore an important and potentially informative group for addressing how diverse predator assemblages partition available prey resources. 2. New World army ants are largely specialist predators of other ants, with each species specializing on different ant genera. However, the mechanisms of prey choice are unknown. In this study, we addressed whether the army ant Eciton hamatum: 1) can detect potential prey odors, 2) can distinguish between odors of prey and non-prey, and 3) can differentiate between different types of odors associated with its prey. 3. Using field experiments, we tested the response of army ants to the following four odor treatments: alarm odors, dead ants, live ants, and nest material. Each treatment had a unique combination of odor sources and included some movement in two of the treatments (alarm and live ants). Odor treatments were tested for both prey and non-prey ants. These data were used to determine the degree to which E. hamatum are using specific prey stimuli to detect potential prey and direct their foraging. 4. Army ants responded strongly to odors derived from prey ants, which triggered both increased localized recruitment and slowed advancement of the raid as they targeted the odor source. Odors from non-prey ants were largely ignored. Additionally, the army ants had the strongest response to the nest material of their preferred prey, with progressively weaker responses across the live ant, dead ant, and alarm odors treatments, respectively. 5. This study reveals that the detection of prey odors, and especially the most persistent odors related to the prey’s nest, provides a mechanism for dietary specialization in army ants. If ubiquitous across the Neotropical army ants, then this olfaction-based ecological specialization may facilitate patterns of resource partitioning and coexistence in these diverse predator communities. 08-Jan-2020

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