Attack Of The Giant Leeches (1959)

Starring Ken Clark, Yvette Vickers, Jan Shepard, Michael Emmet, Tyler McVey
Directed by Bernard L. Kowalski
(actor & director credits courtesy IMDB.com)

A backwoods community is shaken by the deaths of people attacked in the swamp by giant mutated leech monsters, but the local game warden gets no help in proving the creatures exist.

Roger Corman's brother Gene produced this effective picture which I don't think gets the respect it deserves, well photographed and directed in a unique setting for the genre, especially at the time it was made.  The creature design holds up pretty well, and their bloodsucking attacks on their victims while trapped are in an underwater cave are definitely unnerving, following a similar template as used in the Corman-produced Beast From Haunted Cave the same year.  The backwoods characters in the cast, while trading in on some familiar stereotypes, are anchored by Bruno VeSota's general store proprietor, who elicits sympathy as a man detested for his girth by his beautiful and philandering wife, played by Vickers.  They're joined by a capable supporting cast, and Leo Gordon's screenplay does a good job of illustrating the ethical dilemmas facing Clark's game warden while pressure mounts to stop the creatures before their next attack.