Phase IV is an American science fiction film, made in 1974. It is the only feature-length film directed by the noted title designer Saul Bass. It starred Nigel Davenport, Michael Murphy, Lynne Frederick and Helen Horton (who would later provide the voice of "Mother" in Alien).
The film bears some similarity to an earlier film, The Hellstrom Chronicle. Both feature extensive use of close-up photography of actual insects. Both imply that humanity, having failed, must give way to insects, who will now take over from them, in Hellstrom Chronicle insects generally, in Phase IV, ants specifically.
Due to some unknown cosmic event, listed in "phases", ants have undergone rapid evolution and developed a hive mind. A scientific team then begins investigating strange towers and geometrically perfect designs which the ants have started building in the desert. The ant colony and the scientific team, along with a rural family, make war with each other, with the ants making the more effective aggressors. The narrative uses the scientific team as the main protagonists, but also an ant "hero" going about his duties in the colony. The film concludes with the last of the cosmic "phases", Phase IV, which promises a new future for all life on Earth.
Despite the lurid tone of its poster art, Phase IV approaches its subject matter naturalistically, with relatively little melodrama. The film contains relatively little dialogue, mainly relaying the storyline visually.