I have a tall tree in my yard and noticed a lot of large dark ants at the base going into some holes at the base of the tree. There were also a couple large wasps of some kind landing in that area too. I didn't know what was going on and if there is something I can do to stop it. I am thinking the tree must be in some kind of stress? I am wondering if the dark area is from the tree or is it coming from all of the ants back and forth?
The blackened spot looks like slime flux or bacterial wet wood. The insects will feed on the liquid oozing out of the tree. Often times, trees can live a very long time with this bacteria inside. See Penn State's fact sheet about this.