Walt Disney screened the movie because he was interested in casting James Arness as Davy Crockett. However, he was so impressed by Fess Parker as the "Crazy Texan Pilot" that he chose him for the part.
In 1998 Joan Weldon revealed that during shooting, the temperature reached 110°F and both she and Edmund Gwenn were wearing wool clothing. It was even more insufferable for Gwenn, who struggled with advanced arthritis. Although unnoticeable to audiences, he was in pain and was helped off set by his valet.
It was also supposed to be in 3-D. Some elements of the 3-D effects, such as the ants having extreme close-ups and the flame throwers shooting straight into the camera, were used in the film. Although the second eye print was filmed, it was never struck and likely destroyed later.
Was originally supposed to be filmed in color. Two days before shooting began, a nervous studio cut the budget, and the film had to be made in black and white. However, in the opening credits, the title is shown in bright red against a black-and-white background.
The sound that the giant ants make as they approach their prey is a recorded chorus of bird-voiced tree frogs (Hyla avivoca) of the southeastern US. Occasionally a gray tree frog (Hyla chrysoscelis) can be heard on the soundtrack as well, as these species can often be heard together at the same wetland. These distinctive whistling-type sounds were reused in various other films in the years that followed, particularly in Mohawk (1956) and The Black Scorpion (1957).
The camera Dr. Pat Medford is using in the helicopter is a Stereo Realist, which is a 35mm format stereoscopic (3-D) still camera. This is both perfectly natural and ironic since the film itself was originally planned as a 3-D release.
Shortly after the helicopter reconnaissance, a meeting opens with an army officer looking through a Stereo Realist red button viewer. He is evidently looking at 3-D slides taken by Dr. Pat Medford. A second viewer is on the table next to Dr. Medford. This was rather clever product placement, considering the film was originally slated to be shot in 3-D format.
Relating to the "S.S. Viking" incident, there was no cruiser named "U.S.S. Milwaukee" in commission in the United States Navy at the time this film was made. The last ship so named was an Omaha-class light cruiser (CL-5) which was commissioned in 1923 and scrapped in 1949 after service in World War II in both the U.S. and Soviet navies. The next ship named "Milwaukee" would be a Wichita-class replenishment oiler (AOR-2) that would be in service from 1969 until her decommissioning in 1994. Her name was stricken from the Navy's list in 1997, and as of 2007 she is awaiting final disposal at the James River Reserve Fleet, Fort Eustis, Virginia.
The subterranean chase scenes in He Walked by Night (1948) convinced a Warner Bros. executive to use the storm drain tunnels under Los Angeles for the climactic scenes in this film. The original story idea to have the giant ants invade New York City's subway system was scuttled partly due to budget constraints, but mainly because of the horrified reaction of NYC transportation secretary William J. Daley to such a suggestion.
In the movie, James Whitmore and James Arness battle the giant ants with machine guns, flamethrowers, and bazookas, while wearing army uniforms - although neither of their characters is technically a soldier. (Whitmore is a New Mexico state trooper, and Arness is an FBI agent.) However, Whitmore and Arness had previously appeared together as soldiers in combat in the film, Battleground (1949).
The trivia item below may give away important plot points.
WILHELM SCREAM: Can be heard four times in the film. When the giant ants attack the crew of the ship at sea, when James Whitmore's character Police Sgt. Ben Peterson is throttled to death by a giant ant, when a soldier is struck by the falling debris in the sewer and when James Arness gets separated from the rest of the Army and ants try to attack him. The ceiling falls in and while he reloading his weapon, an ant tries to attack him. There's also a scream off-screen from Peterson's partner, Ed Blackburn when he investigates the sounds made by the ants.