ants are a real pain. Many ants bite and the produce formic acid which is the same stuff in stinging nettle (plant) and it is also why some birds grabs ants and rub them on their feathers to release the chemical in order to kill mites - cool, huh? OK< but that's not what you're here for....
If they are on your silkies get the silkies out (with as many ants as possible) and chuck them all - either in your composter or down the toilet. yes, you will forfeit the silkies but you'll also be ridding the silkies of their pain
As for a natural repellent, once they are established there really is nothing that I know of except insect predators, which is not practical in this situation.
I had a problem with small (maybe sugar) ants in Cyrus' cage. They mainly went for (swarmed) any sweet food (fruit) I left on the cage bottom for the free ranging crickets. I noticed that they would hurry back into my plant (ugh - had just repotted). I found some GREAT stuff (not natural) and with some common sense and precautions it can help get any leftover ants. But before I give you those tips you need to find out where they are nesting - was it you I mentioned the channels in the metal frames to in another thread? If not, please read it and get some quick dry caulk (I used DAP brand
DAP easy caulk) and fill in all openings.
OK, for the magic...
TERRO Ant Killer. I use the liquid and place it
outside the cage so no crickets or other "food" items eat it which then might be consumed by Cy. If the ants are small enough they will go find it. There are also liquid filled traps (different from Combat, etc.) , but a small cricket could still get in, eat it and live long enough to be eaten by your cham so you will have to determine the particulars of your own situation - all I can say is that this stuff works great. I got it at home depot - very cheap ($4) What happens is that the workers "bring it back" to the nest and the queen (and drones) will consume and die.
Just keep in mind that if you have a bad infestation you really need to do a major cleaning of the entire cage. Do you have another place you can put your cham for a few days - with minimal stress?
Hope this helps and good luck!!