Don't fret. If your plant is one of the bulbous/semi-bulbous species like ehlersiana, seleriana, bulbosa, etc., ants are naturally attracted to them. These species are referred to as 'myrmecophilic' (ant loving) and harbor ant colonies. You may find a very tiny hole at the base of your plant where they enter. They do the plant no harm whatsoever.
If your plant isn't a myrmeco species then you've probably got something like scale or mealybugs down in the leaf bases. A little soapy water will cure that.

thanks, i'll check for bugs.