These bees have been seen to seize some oncidium flowers for an instant, leaving the oncidium flower when they find no oil, but pollinate other flowers when they make the same mistake again. In another example of pollination systems, some females of certain bee species are known to gather around certain flower clusters. The males tend to pick such flower clusters for their territories, defending this against other insect invaders. When the wind moves the inflorescence, the oncidium flowers apparently look enough like an insect in flight to arouse the aggression of the male bee, which attacks the flower. Oncidium hyphaematicum, planilabre and stipitatum are pollinated in this way.
Most oncidiums have yellow and brown coloured flowers, with some white, and infrequently red.
Clear red colouration is infrequent as most bees are blind to red, the few flowers of red colour often reflecting ultraviolet rays the bees can perceive. The genus contains plants with wide variation in their 2n chromosome numbers, this playing an important part in cross breeding fertility, and may, when more details become known, be an important aspect in a re-evaluation of the whole genus. Many oncidiums are largely, or completely, self infertile, although artificial crossing with related genera such as odontoglossum, brassia, miltonia, etc. is possible. Naturally, individual species retain their purity by growing over a distinct geographical or altitudinal range, or by differing flower colour, form, callosities or scent, attracting different, and often very specific, insect pollinators. It has been suggested that the genus oncidium should be broken up into a number of different smaller genera.