I have had better luck putting a shell NEAR, but not ON, a fire ant hill.
Even fifteen or twenty feet away the ants will find it and clean it out.I
will put a milk crate and four cement blocks over it to deter raccoons or
seagulls from dragging it away.

The fire ant poison I use says to sprinkle it around, but not on, the hill.

I once caught a small shark, and it was hooked so badly that it bled to death
before I could release it. (I'm a big promoter of catch and release). Anyway,
I decided to cut out the jaws, and I placed them directly on an ant hill. Not
one ant took advantage of this, and the jaws rotted and fell apart.

Scott
Florida