To assay the effect of area and predators on invasion success, spiders were introduced onto islands that were large, with lizard predators; large, without lizard predators; or small, without lizard predators. Short-term survival was greater on islands without than with predators; area had no effect. Spiders initially increased substantially on both groups of islands without lizards, but after 5 years they nearly died off on small islands while persisting on most large islands; populations in the presence of predators never increased above initial sizes. Results show how predators as well as area are important in determining invasion success.