Though usually beneficial, bats sometimes are a nuisance to humans (Greenhall & Stell, 1960), or may even constitute serious economic problems and health hazards. Most important in this respect are the vampire bats, especially of the genus Desmodus, which are abundant from northern Argentina through the whole of Latin America to the north of Mexico. The agricultural problem is caused on the one hand by weakening of the cattle through loss of blood, making them more susceptible to diseases and parasite infestation, as well as by transmitting paralytic rabies (Derriengue). An organized control of vampires has only been established in Trinidad (Greenhall, 1958). On the American continent some control efforts were undertaken sporadically by local veterinarians and cattle owners. They comprise mainly dynamiting or fumigating caves or burning hollow trees. As the controllers usually cannot distinguish between a vampire bat and another bat, they destroy more benefical bats than vampires and do more harm than good.