After 50+ years, I finally understand the movie's title...

"The BLACK Scorpion"

Okay - yeah - it's "black" because, for the scenes of people stampeding out through Mexico City (see my thread on THAT topic as well), presumably the money ran out for matte printing and some other process was used to get the scorpion in the same frame as the people.

The process used looks something like simply double exposure, using a heavily darkened print of the scorpion to matte out the background in the "people" footage.

The result is a "black" scorpion.

I can only imagine the movie's title was an afterthought by the producer to prepare audiences for what would otherwise seem a shortfall in special effects (it still is, but to naive movie audiences in the 1950s maybe not so much if such a foreboding title was what pre-sold the movie).

It's a shame - because the final battle sequence is among the best in the "giant insect" genre.

"Don't call me 'honey', mac."
"Don't call me 'mac'... HONEY!"