ants in ground around tree

[jerseydevil]

To make a long story short, the other day i noticed a lot of ants "working" in the ground under (about 5 feet from the trunk) a very old (100+ years) and large oak tree in my yard. They seemed to tunneling in or out. There were many holes about 1/8-1/4 inch around, in a grid like pattern. The total area of the workzone is about 4 feet square. The ants were big and black. I don't know if they were carpenters or what. I am afraid they have a nest down there and will prematurely kill the tree. What can I do.
Thanks for the time. I am new to this site but I love trees and have done a little tree work and maintenance. I will be around for a while.
:Eye:

 

[MasterBlaster]

Throw one of these down to confuse em!

http://***************/treehouse/files/picture_369__small__121.jpg

 

[treeseer]

mb that looks like the meatlover's; I think depending on the ant they may prefer veggies.

Ants tunneling in the ground are good for the tree, aerating the soil, eating, passing out fertilizer, doing all those ant things. If you have big black ones going INTO the tree, that's a sign of decay, but even they seldom warrant treatment or panic.

Send a picture if you can, and attend to the tree's needs; check the link below.