This red snake was hunting quite determinedly for something on and in the ground. It didn't seem to care that I was only a meter away taking photos.

Thanks to all the iNat help, and a very large book on snakes in the Americas in the Texas State University Library, it appears that this is Micrurus diastema alienus.

Several different people told me this was a non-venomous snake. They suggested close to 10 different incorrect species. Never mess with snakes you don't know; especially in foreign lands! :-)