Filmed in Mexico, The Black Scorpion was the last theatrical feature to bear the imprimatur of special-effects maven Willis O'Brien. Allegedly an outgrowth of a ten-minute "test" film, the story is set in motion by a volcanic eruption which releases dozens of giant scorpions from a cave. American geologist Richard Denning and his cohorts try to drive the scorpions back into their lair, but the huge arachnids are soon at large in civilization, munching on innocent bystanders as they go their merry way. The authorities are able to destroy all but one scorpion, who unfortunately is the nastiest of the bunch. The climax takes place in a Mexico City bullring, where the scorpion does battle with a fleet of military helicopters.
by Hal Erickson synopsis