Warning signals of aposematic organisms often include patterns that contrast with background coloration, though controversy exists over their importance. Many dendrobatids have contrasting colors, but no work has established whether these are anti-predator components of the warning signal. We used 840 clay frog models to test whether a black spotted pattern on the red dorsum of the poison frog Oophaga pumilio (= Dendrobates pumilio) from Costa Rica enhances the aposematic signal. Model type, patterned or not patterned, did not predict predation. However, we did find evidence that background (i.e., contrast between an aposematic organism and its environment) influenced a predator's attack decision because models on white paper (higher contrast) were attacked significantly less than models on leaf litter (lower contrast). Our results indicate that the pattern of Costa Rican O. pumilio does not influence predation. Our results also support the hypothesis that novel backgrounds evoke a neophobic reaction and can affect predation rates.