I'm wondering if orchids provide extra floral nectaries for ants, such as are seen on some acacias in the tropics. The ants may then provide protection by attacking invertebrate (or vertebrate) herbivores. Or, do they just exude sugar/honeydew randomly?
Check out Myrmecophila, its a south american genus which has ants form colonies in its hollowed out pseudobulbs. The wikipedia page says it produces nectar from its penduncles.