Ants hate, hate, hate peppermint.  You can use peppermint essential oil or
peppermint spirits (or even peppermint mouthwash, in a pinch ...) to keep
them away.  Best bet is to leave cotton balls with peppermint essential oil
in areas which you would like them to stay away from.  It's a repellant; it
won't kill them.
 
As for killing them, if you are so inclined .. I understand that borax
works - the good old 20 Mule Team stuff.  Apparently, they take it back to
the nest, and it kills them.  I usually just try to repel them, though ..
not kill them.
 
- Ela
[Posted in FML issue 2714]