I have a theory about that - the disappearance of the horny toad. When the fireants move in, out go the army ants and that is what the horny toads feed on. I believe the fireants do kill them, but mostly they kill or run off their food source. When I moved into this house, beach house a half hour north of Corpus Christi, there were a bunch of the toads living in the backyard. And, I had a whole nest of army ants back there too. Now I have only fireants around, no more army ants and no horny toads.
I have also found a lot of horny toads when driving near Oc Fisher Lake near San Angelo. I also found lots of army ant mounds there too. And no fire ants.
Growing up in San Antonio we had horny toads everywhere. I just loved those little dudes. They were so scary, in a prehistoric kinda way, and yet they were such friendly little guys. I feel bad for their disappearing. Reminds me of the Don McLean song Vincent -- 'This world was never meant for one as beautiful as you'.
Up until 1969 I lived in Robstown and I remember them well. After that we moved to an area inbetween Houston and Galveston and I've never seen a one in the wild here. When we went back to visit family the little creatures seemed to have disappeared. I was told the fire ants killed them, but the loss of their food source also makes sense.