According to director Bernard L. Kowalski, producer Gene Corman didn't want to pay the grips the extra money for pushing the camera raft while they were filming in the Pasadena Arboretum in the water, so first Kowalski and his brother did it and later Corman put on a bathing suit and did it himself and ended up in a hospital for a few days.
The giant leeches are played by actors in sack-like suits made of thin black plastic raincoat-like material and complete with fake "suckers" sewn on.
The music score for this film was a stock score used previously in the film Night of the Blood Beast (1958), also produced by Gene Corman, brother of Roger Corman (it can also be heard in Beast from Haunted Cave (1959)).
Shot in eight days for $70,000 utilizing the same basic crew as "Night of the Blood Beast" and existing sets on the Chaplin backlot.
Viewed on an episode of Mystery Science Theater 3000
Lead actress Yvette Vickers promoted the film by stripping off for a Playboy centerfold.
The film's Spanish title is "El Pantano Diabolico", meaning "The Diabolical Marsh."
In the public domain.
During filming, producer Gene Corman was hospitalized with a bout of pneumonia.
The film was released by American International Pictures on a double bill with A Bucket of Blood. Later, in some areas in 1960, Leeches played on a double bill with the Roger Corman film House of Usher.
Attack of the Giant Leeches was one of a spate of "creature features" produced during the 1950s in response to cold war fears; a character in the film speculates that the leeches have been mutated to giant size by atomic radiation from nearby Cape Canaveral.
A remake of the film, directed by Brett Kelly and written by Jeff O'Brien, was released on July 7, 2008.
In July 1992, Attack of the Giant Leeches was featured as a fourth-season episode of the film-mocking television series Mystery Science Theater 3000. It was also featured on the nationally syndicated horror host television show Cinema Insomnia, and in the second episode of season 5 of Shilling Shockers, a New England-based television show hosted by the witch Penny Dreadful XIII.
Being in the public domain, Attack of the Giant Leeches has received numerous bargain bin DVD releases. The MST3K version of the film was released on October 26, 2004 by Rhino Home Video as part of a box set, The Mystery Science Theater 3000 Collection: Volume 6. Cheapskate Theater released an HD download of the film on June 7, 2016 featuring a new introduction by Toby Radloff and Radloff outtakes and bloopers.
Some critics have characterized the film as one of the worst science fiction horror films made, and one of the all-time worst films of any kind, even suggesting that it may be worse than Ed Wood's legendarily bad Plan 9 from Outer Space.
The film was shot over eight days, including outdoor sequences at the Los Angeles County Arboretum and Botanic Garden.