Immediately following production of this film, Ski Troop Attack (1960) was filmed on the same location in the South Dakota Black Hills. Both films featured much of the same cast and crew.
Roger Corman and Gene Corman partly chose their filming location in the Black Hills because they were encouraged to come by the Chamber of Commerce in South Dakota. The Chamber of Commerce offered financial incentives in order to ensure that this, and future Corman films, would be shot in their state.
The cave in the film was actually an abandoned mine in Deadwood, South Dakota.
Some scenes required the actors to fire guns inside the eponymous cave (which was actually an abandoned mine). The reverberations from the gunshots made part of the mine's ceiling collapse. None of the cast or crew were injured, but they were greatly unnerved by the situation.
According to Chris Robinson, the actor who portrayed the monster, he added aluminum stripping to a plywood base, then covered the frame with chicken wire before wrapping it in sheets and muslin in order to create the monster's skeletal base. He then soaked the frame in vinyl paint in order to waterproof the design, since it had to be used in the snow. The creature's head was fashioned out of quarter-inch aluminum wire, which was then encased in steel wire and wrapped in muslin. The creature's fangs and teeth were also constructed with aluminum wire. Robinson then placed putty and patches of crepe hair onto the design before adding spun glass in order to give it a cobwebby appearance.
This film debuted as a double feature with The Wasp Woman (1959) upon its theatrical release.
The Corman brothers, Roger Corman and Gene Corman, had grown tired of making films in Bronson Canyon and the Los Angeles Arboretum (frequent shoot locations for their films) so they moved to South Dakota's Black Hills to shoot this film and Ski Troop Attack (1960).
Director Monte Hellman was introduced to Roger Corman through his wife, Barboura Morris, who had previously acted in some of Corman's films. Corman gave Hellman the director's job for this film on the spot. According to Hellman, he offered the job through a handshake agreement and there was no official contract. Hellman recalled that "We didn't have a contract or anything. Just a handshake. And Roger's handshake was better than most people's contracts."
Charles B. Griffith wrote the screenplay for this film by reworking his own script from Naked Paradise (1957).
A version of this script, which was itself adapted from Naked Paradise (1957), was reworked to provide a more comedic angle in the horror-comedy Creature from the Haunted Sea (1961). Each script was written by Charles B. Griffith.
According to Monte Hellman, the film's director, his salary for the picture was only $1,000.00.
Chris Robinson, the actor who portrayed the monster, grew rather attached to the constructed beast, which he nicknamed "Humphrass."
Whilst filming scenes in the cave (actually an abandoned mine) the air grew very stale and some actors found difficulty breathing. The film crew began pumping fresh air into the mine, however the issue was never completely resolved. The cast and crew would shoot scenes whilst breathing the bad air and then rush outside to get fresh air after each take.
Directorial debut of Monte Hellman.
The monster was based on the appearance of a wingless hangingfly.
As well as his $1,000 director's fee Monte Hellman claimed to have received 2% of the profits - which he said came to $400 over the next five years.
Although the movie was apparently released in late 1959, some of street scenes must've been added later. As the criminals drive around in the opening scenes there's several cars shown that are 1961 models (two Thunderbirds, a Chrysler, a Corvair--this could be a '60, and an Olds Cutlass).
It was Roger Corman's practice to stretch his budgets and make the most of a location by shooting a second film. The snowy South Dakota location led to the creation of "Ski Troop Attack" (1960).
Despite the white make-up in Frank Wolff's hair and mustache that was intended to make him appear much older, he still looks his actual age: 31. In fact, he was only one year older than the "youthful" lead, Michael Forest.
The film was shot with the understanding that a sequel would soon be in the works, with the surviving characters reprising their roles. The plans for the sequel, however, were never realized. This film's open-ended conclusion was a result of the nixed sequel idea.