If you want to keep away from pesticides, there is an "old-timer" trick
using borax and sugar that might be kinda.. nasty.. on the little
fellers.

Apparently a chemical reaction takes place and the ants blow up
(assuming not literally, they just get too big for their
chitin/whatever you call it) and they burst. Other ants eat that, and
it goes on in a chain reaction.

Sorry I don't have the recipe handy, I think maybe I read it in an old
back issue of mother earth news or something along those lines.