There are hundreds of species of ants in the US.  My understanding is that there are few if any that will eat healthy wood.  I believe it is rotten wood they eat.  Now that may impact a tree in it's ability to heal - have no idea.
  Here in NM, what I call a carpenter ant is a HUGE ant and are fairly easy to control with various baits.  They are nocturnal so I've gone out at night and found their trails.  Not like a typical ant trail in that it will be one ant every 2-3 yards instead of a steady stream.  Anyway, I've personally had good luck with Maxforce products - both the granuals and the "gel" types.
  While the products at the hardware stores can work - I have taken to using the same stuff the pro's use.  Easily purchased on the internetIt is also perfectly legal....
  For these ant bait type products the risk is very low - small amounts strategically placed.  For some of the other products consumers can buy  I worry a bit due to general availability.  The labels need to be clearly read and understood as I suspect some of them are related to the decline in the bee population that has been going on lately.
Anyway, just google "do your own own pest control" and do a bit of reading - can save you a ton of cash.  I paid around $40 for an ant control "kit" recently.  Last time I did this, it lasted me for about 2 years.  Compared to $40/visit from the pro's.
-Chak