The reason both chalk and Comet cleanser keep the ants at bay is because they are both made from D.E. or Diotamceous Earth. (You would NOT believe the crap I learn because I keep chickens!) D.E. is sold in food grade and pool grade, for swimming pool filters. It's in your toothpaste and flour and will not hurt you or your pets. But for insects it is deadly. Any pest company who used natural substances will be using D.E. and Borax to kill pests.
"Diatomite is also used as an insecticide, due to its physico-sorptive properties. The fine powder absorbs lipids from the cuticle, the waxy outer layer of insects' exoskeletons, causing them to dehydrate. Arthropods die as a result of the water pressure deficiency, based on Fick's law of diffusion. This also works against gastropods and is commonly employed in gardening to defeat slugs. However, since slugs inhabit humid environments, efficacy is very low. Beekeepers are apparently experimenting with it, to keep small hive beetles from breeding. It is sometimes mixed with an attractant or other additives to increase its effectiveness. Medical grade diatomite is sometimes used to de-worm both animals and humans. It is most commonly used in lieu of boric acid, and can be used to help control and eventually eliminate a cockroach infestation."