Originally Posted by joecaption
Could be as simple as when you killed the hornets some critter saw them and just dig out the already cracked concrete block to get to more of them.
That would explain the situation. I'd have thought nothing would eat hornets because it would be toxic to ingest the venom, but perhaps it's neutralized in their digestive system. Although it can't be good for anything to consume the residue from the stuff I sprayed.
The rest of the foundation seems fine. The only cracking/deterioration is around the door sill and drain hole, which is all you see in the photos.
Thanks for the reply!