When backwoods Florida shopkeeper Dave Walker (Bruno VeSota) discovers his hot but hostile wife Liz (Yvette Vickers) has been having an affair with his best friend Cal Moulton (Michael Emmet), he pursues the offending couple into the swamp with a shotgun. But before he can exact his revenge, the pair are dragged under the water by a couple of enormous slug-like creatures.
While Dave is arrested for the murder of Liz and Cal, game warden Steve Benton (Ken Clark) conducts a search for the victims, aided by his girlfriend Nan (Jan Shepard) and her father Dr. Greyson (Tyler McVey). Lots of footage then ensues of Steve and Nan rowing through the Everglades, even as people continue to disappear. Finally, Dr. Greyson uses dynamite — against Steve's orders, no less — to inadvertently dislodge a bevy of corpses, giving the heroes an idea where to look for the other victims. Steve dons an aqualung and a speargun and dives down to do combat with the giant leeches before more dynamite is used to finish them off.
This movie leeches off of the following tropes:
- And I Must Scream: The leeches keep their victims (barely) alive in order to continue feeding off them.
- Artistic License – Gun Safety: Steve horrendously violates the second rule of gun safety when he rescues a woman and then holds her to his chest, all while his gun is pointed directly at her face.
- Asshole Victim:
- Just listen to the way Cal talks about his "best friend" Dave, whilst having an affair with Dave's wife.
- Liz, by way of contrast, is given a touch of sympathy via her Freudian Excuse.
- Attack of the Killer Whatever
- Big Bad Duumvirate: There are two leeches attacking the town.
- Bittersweet Ending: In the end the giant leeches are destroyed, but with the cost of swamp's ecology. But then there's the below to consider...
- Cassandra Truth: The film opens with a local drunk telling everyone about the strange creatures he's seen in the swamp, but everyone dismisses the sighting as a case of the DTs. The drunk is dead a couple of scenes later.
- Daddy's Girl: Nan treats Steve's actions towards her father as borderline unforgivable, implying that Steve is being cold, cruel and pigheaded. Steve is, in fact, remarkably lenient and patient with her father, offering him multiple warnings, making his position clear several times, and is technically in the right when he talks about what his job responsibilities are and what he's required by law to do.
- Deep South: Quite a few side characters are played as total local yokels.
- Driven to Suicide: Dave hangs himself in jail when no one will believe he didn't kill his wife.
- Event Title
- Exactly What It Says on the Tin: It's a movie about an attack of giant leeches.
- Freudian Excuse: Liz blames her long streak of bad relationships for landing her in Dave's hands.note
- Hillbilly Horrors: Giant leeches terrorizing a swamp town.
- Men Are the Expendable Gender: One female victim among four male ones; the woman even manages to outlive Those Two Guys who are captured long after she is, giving the audience a false hope that she will ultimately be rescued. Furthermore, the eventual discovery of the men's bodies is played as a shock sting, while the discovery of the woman's is treated as more tragic.
- Mistaken for Murderer: Dave only meant to put the fear of God into Liz and Cal; he wasn't counting on giant leeches.
- Nuclear Mutant: A Hand Wave mid-film suggests that the leeches were mutated by waste run-off from nearby Cape Canaveral. (Cape Canaveral never did any nuclear experiments.)
- Police Are Useless: The local sheriff refuses to partake in Steve's search for Liz and Cal, preferring to believe that there are no monsters in the swamp and that Dave shot Liz and Cal in a jealous fit. He publicly maintains this attitude even after Cal's body is recovered and after an autopsy proves that he was killed by something like a giant leech, not a shotgun; he even goes so far as to (vaguely) threaten Steve for "poking around in other people's business". He is convinced only when he personally witnesses Liz's body rising from the swamp.
- Remonstrating with a Gun: Dave chases Liz and Cal with a shotgun when he discovers their affair.
- The End... Or Is It?: The last thing heard in the film is the sound of the leeches 'gurgling'. Implying that some others survive.
- Those Two Guys: The leeches' final two victims, who are captured even as they search for Liz and Cal.
- Ugly Guy, Hot Wife: Dave and Liz.
- The X of Y