Larvae of Epargyreus clarus (Hesperiidae), the silver-spotted skipper, inhabit leaf-and-silk shelters that they construct on their leguminous host plants.  In the field Polistes spp. (Vespidae) wasps land on the shelters, quickly extracting and killing the larvae within.  In marked contrast, wasps that emerged from field-collected colonies maintained in the laboratory visited and examined leaflets bearing sheltered caterpillars, but only rarely did they extract and kill the sheltered larvae.  However, after killing and processing an unsheltered larva that was visible on an opened leaf shelter, a majority of foragers subsequently extracted and killed larvae from closed shelters.  Wasps that killed and processed an unsheltered larva away from a leaf shelter, on the other hand, generally did not later open shelters.  Thus it seems that experience with an exposed larva in the context of its shelter is necessary in order for a wasp to be able to prey on sheltered larvae.  We conclude that the wasps must learn to associate the taste of the larva with shelter-related cues, such as presence of leaf damage and silk.  In nature, this initial exposure may occur when the larva is visible in or near its shelter, perhaps when feeding or constructing a new shelter.  Learning opportunities will thus depend on larval density.  Our results demonstrate that invertebrate predators can learn to overcome their prey’s defenses, and are therefore able to make use of previously inaccessible prey.