Crazy ants DO kill fire ants! Since we became infested with them (Texas upper coast) we hardly see any fire ant mounds. Crazy ants are harder to kill even than fire ants, though. They do like to muck up electrical outlets, and will use an extension cord or a water hose left on the ground for a raised ant highway. I have to put my dog feeding dishes in a larger container filled with water to make a "Moat" around them when the ants are really bad to keep them out long enough for the dogs to eat. I've seen them eat dead roaches, and a coon I shot one morning was covered with them in just a few minutes after he hit the ground. Generally, I prefer them to fire ants, but they will bite humans, just don't hurt nearly as bad.
