The acoustic preferences of Corethrella blood-sucking flies were studied in northeastern Costa Rica. These flies are known to be attracted to the call of túngara frogs, Physalaemus pustulosus , and have been shown to prefer complex over simple calls produced by these frogs. Corethrella flies were tested with túngara frog calls in a population where such frogs are not present. The flies showed to be attracted to the foreign call in great numbers. This study suggests that the blood-sucking flies have a flexible acoustic template.