[genewitch]

boric acid is extremely effective. I use only boric acid, and i live in a forest. I put the powder under the stove, around the edges of cabinets, under the fridge, etc. After a new dusting (every 3-4 months or more) the carcasses will show up, maybe a half dozen.

And if you want a spray to kill insects you can see and watch, IPA (rubbing alcohol) and mint extract works fine. Except against centipedes.

For ants boric acid works sometimes, but so does talc or diatomaceous earth. However this stops them from tracking while you clean up whatever they're after. In my experience dealing with sugar ants, pissants, RIFA (fire ants from south america), fire ants (red ants in CA), and so on; the only 100% effective way to get rid of them is to put popcorn kernels in a blender and chop it till everything is smaller than 1/16" or so, and leave that somewhere moisture can't get to it. Ants eat it and bring it back to the nest to eat and then explode. I can't verify they actually explode, but that's the mechanism of action.

AFAIK boric acid and DE aren't harmful to humans, and corn and rubbing alcohol are usually fairly safe.