oh yeah, forgot to ask...will the ants do any damage to the tree over time, or are they just more of a nuisance instead?

I have the same problem with some of my potted plants, but haven't noticed any harmful effects. It's mainly a pain when it comes to repotting the plants. The ants might actually be beneficial in helping to aerate the soil. However, some ants have symbiotic relationships with aphids and will actually "farm" them, so you might need to watch out for that.

I have six different maples in pots on a self made "maple table" and there a few ants coming out of the pots from time to time. Since there are only a few ants I am not worried about the plant itself unless I witness one or more going after the leaves. All of my maples are one year grafts purchased this time last year.

I also planted a flowering pear in the back yard two months ago and aphids completely infested that tree (took care of them but good), but left the maples untouched, so you probably won't have an aphid problem.

I, too, have major problems with fire ants, they are every where, and in my JM pots, and around the JM's in the ground, and what I do is put ant killer around the pots, and inside the pots, and around the trees and so far I have not had any problems with the maples. -Ivy

Ants do create problems. My once graceful looking seiryu maple had been sabbataged by big ants. They set up colonies in side the pot and climb (???walk??) on branches. Eventually the maple will look sick and distorted. The whole process is very fast so you need to act immediately.

My advice is you have to either flood them out by placing a plastic bag under the pot to ensure water doesn't escape early in the morning. If that doesn't work, you need to change the potting mix - wash the current soil out, and pot the maple again.

Have you tried the liquid ant killer that the ants eat like Terro? You can get bait stations that you could try just setting on the dirt and see if that works. Something like this:
Terro Liquid Ant Bait

I use the regular Terro all the time and it works great but these stations would help for outdoor applications, plus they keep the animals out.

I don't think it's the ant themselves that cause the problems. Some ants "farm" aphids, which can cause serious damage to JMs and other plants by sucking their sap. The ants protect the aphids from predators and feed off the honeydew that the aphids excrete.

The ants themselves shouldnt hurt the tree...the airation of the soil will actually help the tree. But, yes the aphid
problem is another issue. If you see any small flee sized bugs along the stems (particularly underneath), then you have a problem. I have successfully flooded all of my ants out by adding drip irrigation that turns on twice a day.

But if you wish to kill them, which would be a good idea because flooding them will only cause them to relocated into your yard, I would suggest amdro fire ant killer. It isn't liquid so it shouldnt harm the tree (placing it around the pot will suffice). It is a poisoned bait that the ants collect and eat (carrying some to the queen which is required to erradicate the colony).