Attack of the Giant Leeches (1959) - Trailer

In the Florida Everglades, a colony of larger-than-human-size, intelligent leeches is living in an underwater cave. They begin dragging local people down to their cave where they hold them prisoner and slowly drain them of blood.

This film was one of a spate of monster movies produced during the 1950s in response to cold war fears. In the film a character speculates that the leeches have been mutated to giant size by atomic radiation from nearby Cape Canaveral. The leeches themselves can also be interpreted as a sort of allegory on the supposed dangers of covert communists lurking undetected in even unlikely parts of America. As with many of these films, the analysis can be more entertaining than the film itself. - wikipedia