Ants in your tortoise pen?
Most can be controlled with a sugar/boric acid combination.
To use, soak a few cotton balls with it. Put them in a small plastic
container (margarine or > )with a few small openings in it for
them to get in. Be sure to Freshen it 1-2 times a week. I also put a
brick on top so other curious creatures could not get in.
This is a slow acting 1 percent solution to get them to take some back to the nest and even feed the queen. After a few weeks changing to a 1/2 percent should keep them gone.