The timing was right. Art house sex films were all the rage and the marketing in the States was simple and brilliant, taking good advantage of punters seeking cinema kicks during the dawn of the sexual revolution. A phone number was published for people to call who wanted to know what the title meant. The bewildering erotic-horror element and the hallucinatory visuals and dialogue were not what many of them expected.
Old-timers in the Manhattan theatrical exhibition business told me it did very well at the box office. The put-downs by Canby and Ebert didn't hurt. Newspaper of the subway crowd, The New York Post, gave it a good review. The gloss of Euro-sophistication gave it a veneer of respectability that the crude sleaze of routinely shot American sexploitation films lacked. Viewers didn't feel the urge to slink out of the theater trying not to be seen.
In today's DVD and streaming world, with thousands of independent theaters now vanished from the landscape, without titillating ads in big city newspapers, Succubus-style films released today would be quickly forgotten.