Shmu is waging vicious war on ants at present, when I saw the thread title on the main page I thought she'd had a turn of conscience.
We decided boiling water is probably more of an instant kill than powders or liquids, and generally kinder to the environment.
Me and the boys had hours of fun watching the critters when I lifted a large paving slab a few weeks back, the network of tunnels underneath was amazing and they all went potty trying to grab all the eggs and move them somewhere safe before they cooked in the sun.