I have had ants in my compost bin every year, I emailed a gardening magazine, they said to leave them as they will help with the compost breaking down, and when you tip the compost out they will disappear, and that is exactly what happens every year. I also get them in the greenhouse as I have slaps in mine, I just put power in the gaps and just put up with them, my pots are outside from the spring so they do not do too much damage. Slugs are going to get it this year as well but I have frogs in my garden so they do most of the work of getting rid.