Aspartame

From mercola.com:

Got an Ant Problem? Use Aspartame
For all the dire health problems associated with aspartame -- the worst of them being cancer -- the original "anything-but-sugar" substitute may have an ideal purpose to exist, not as a food additive, but an ant poison.
Already aware of aspartame's origins as a toxic chemical, a health conscious consumer with an ant problem emptied one packet of aspartame in the corner of each of her bathrooms two years ago. The "sweet" solution worked brilliantly, as she's seen no signs of carpenter ants crawling around for the past year.
Aspartame may be just the thing for getting rid of fire ants (impervious to many poisons) too, although this solution takes a bit more effort. Initially, fire ants ignored their aspartame treat until a light rain moistened it. After the rain, however, the fire ants came back with a vengeance, taking the aspartame back to the mound by the hundreds. Within two days, any evidence of fire ants existed at all, save for an empty mound, vanished.
No mystery aspartame works like a pesticide, as the asparctic acid contained in this toxic product is a well-documented excitotoxin that cause specific brain cells to become excessively excited to the point they quickly die, just as both kinds of ants did.
Makes you wonder if aspartame is a far safer, better alternative to getting rid of lawn and home pests than the average toxic pesticides found at your neighborhood hardware store...
Idaho Observer June 2006

(So the idea is, if it kills ants, it can't be THAT safe for humans, either! This is one of the first things we were convinced to eliminate. So long, diet sodas [and many other "diet" foods, too, check your labels]!)