The Black Scorpion (1957)

Starring Richard Denning, Mara Corday, Carlos Rivas, Mario Navarro, Carlos Muzquiz

Directed by Edward Ludwig
(actor & director credits courtesy IMDB.com)

A pair of geologists in Mexico trace savage killings in the wake of a volcanic eruption and earthquake to a horde of giant scorpions, freed from their subterranean lair by the disaster.

Another of the giant insect movies of the 1950s, this one boasts excellent stop-motion animation effects overseen by Willis O'Brien, who pioneered creature effects of this kind in the classic King Kong.  This film doesn't compare to that masterpiece, but remains a fun effort, much in the same vein as 1954's Them!, with Denning and Rivas tracing the beasts back to their underground nest and attempting to re-trap them inside.  Although O'Brien and his team supplement the animation with effectively grotesque mockups of the scorpions' heads, these aren't integrated too well in the film, and according to Wikipedia, a number of scenes where we only see the scorpions' silhouettes represent unfinished work by O'Brien's unit because they ran out of money.  Nevertheless, I've found this to be one of the more enjoyable monster pictures of the 1950s, and one well worth revisiting to experience and appreciate O'Brien's wizardry.