Attack of the Giant Leeches (1959)

In a community near a swamp, a local dweller sees a couple of giant monsters but nobody believes him. Later, the cuckold Dave Walker finds his slut wife Liz Walker cheating on him with his friend Cal Moulton. He chases the couple through the swamp, and forces them to jump into the water. The leeches take them and shocked Dave is arrested and accused of murder. Two other locals decide to look for the bodies of Liz and Cal to get the prize of US $50.00 per body, and also vanish in the swamp. Finally, game warden Steve Benton organizes a patrol to investigate the caves under the swamp, finding the lethal giant leeches.