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Chemical irritants useful as repellents for brown treesnakes (Boiga irregularis) were identified. Exposure to various compounds produced a range of intensities for locomotory behavior in snakes. Essential oils comprised of 10 g liter -1 solutions of cedarwood, cinnamon, sage, juniper berry, lavender and rosemary each were potent snake irritants. Brown treesnakes exposed to a 2-s burst of aerosol of these oils exhibited prolonged, violent undirected locomotory behavior. In contrast, exposure to a 10 g liter-1 concentration of ginger oil aerosol caused snakes to locomote, but in a deliberate, directed manner. We also tested specific compounds, all derivative of food and flavor ingredients. 10 g liter-1 solutions delivered as aerosols of m-anisaldehyde, trans-anethole, cineole, cinnamaldehyde, citral, ethyl phenlacetate, eugenol, geranyl acetate or methyl salicylate all acted as potent irritants for brown treesnakes. The individual ingredients were classified using cluster analysis into groups that promoted different levels of response by snakes. This study is the first to systematically investigate the irritant potential of natural products for snakes. These data will be useful in the development of practical pest management tools for snakes.