Ants are great, unless they get into your house, kitchen, and then your Lucky Charms! then they are all bad!
Boric acid ant bait:
on stove top mix 1/2C Water with 1/2 C Sugar until disolved, then add 1 TBSP BORIC ACID. Place this mixture away from pets/birds/ stuff that will drink it, except for the ants.
Place the mixture in bottle caps where ants frequent and when they find it they will eat it and share it with the colony, and it should knock the colony back by a good amount , if not all the way.
This stuff will work too.
Ants in your garden are generally not a bad thing, in fact they can be a very good thing, fighting off the bad insects. However they can make a kind of "nursery" for aphids . aphids are bad because they cause problems with your plants (citrus and the like) and the reason why ants like them is they poop out a tasty sugary stuff that ants eat up! and to keep this source of "candy" they will fight off the predatory insects that would naturally feed on aphids.
Thus the boric acid bait comes into play.
so get out there and protect your fruit trees from aphids by knocking back those ants! or just rid them from your home.