Occasionally, ants seem to love "living" in one or two of my staghorns. I am growing the stags outside, under large oaks from April through late October-mid November. Just before bringing in the stags to overwinter, I typically will fill a large tub with water and hold the staghorns under-water for a minute or two. If there are insects, some will float to the top. For those plants I just sprinkle a tiny bit of Orthene Fire Ant Killer over the plants' base. By the following day, all the ants are goners and I bring the plants inside.
Of course, I am not dealing with huge plants, those far too large to "dunk".
@Daisyl, your plant is wonderful but I simply can't allow my plants to get anywhere near that size any longer. I am not strong enough to lift/move heavy plants, and now with the back surgery, I have to be doubly careful with lifting.