Correlates of ant nectarivory have been investigated in a sample of 75 insect-pollinated, nectar-producing southern Spanish plant species. Ants exploit floral nectar opportunistically. Variation among plant species in sugar secretion rates and flower location relative to ground level do not influence either the chances of ant visitation or the identity of ant species involved. Mechanical restrictions on nectar accessibility (tubular corollas, occlusive structures) decrease nectar thievery, Some evolutionary trends in floral morphology usually related to a decrease in the range of effective pollinators alone may simultaneously be interpreted in terms of increased plant adaptedness to exclude non-pollinating insect nectarivores. © 1984 Masson.