While preparing to shoot the sequence where Leiningen pours oil on himself to repel the ants, Charlton Heston was told that oil would ruin his wardrobe so syrup would be used instead. Heston spent a miserable day on location as the "oil" attracted every insect for miles.
Charlton Heston improvised during the argument scene between Eleanor Parker and himself. It was not scripted that he splash perfume all over her. This move intensified the action and a surprised Parker was able to react accordingly.
William Conrad, who plays the commissioner in this movie, played the lead role of Leiningen four times in radio adaptations of the original Carl Stephenson story: three times in 1948 on the radio program "Escape" and once in 1957 on the radio program "Suspense".
A remake was once in development in 2004 with Jonathan Hensleigh hired to write and direct the project but according to Hensleigh himself, once the regime change happened at Paramount, there was no longer any interest in making the film and has been since abandoned.
When Leiningen is showing Joanna around his plantation (about 33 minutes into the film), there is singing, presumably by native workers. They are singing in remarkably good English, and the most discernible lyric is, "We are the Polee." The singing is not closed captioned, so spelling and additional lyrics are unknown.
The trivia item below may give away important plot points.
Despite this film being marketed as a movie about killer ants, the first 2 acts of this film have nothing to do with the ants. In fact the ants are not even mentioned until 50 minutes into the movie and do not appear until the one hour mark, the films entire runtime is only 1h 35m.