There are ants in my window at my parent's house. I can see where they were coming in. I used Rope Caulk to seal the slit in the window pane. This sticky stuff worked pretty well UNTIL THEY ATE THEIR WAY THROUGH IT. So I have Industrial Strength Army Ants.
I just squished another glob of the caulky stuff right on top of them. The dislocated ants that wandered up later were relocated to government housing and given a nice pension.
Mel is being extra sweet. Must be an earthquake coming.
If they are sweet ants like the ones that I used to get in Florida, this stuff works:
It's a gel that you leave at the place where the ants are coming in. They think it's food, bring it back to the nest, and it kills them all. Very effective.
That's only if the caulk still fails you, though.