The Black Belly of the Tarantula (1971)

When nymphomaniac Maria Zani is murdered, her ex-husband and insurance broker Paolo Zani becomes the prime-suspect of Inspector Tellini. Then the saleswoman Mirta Ricci is murdered in the same modus operandi - both victims had been paralyzed by acupuncture needles with poison introduced in their necks and their bellies had been ripped open with a knife with the victims still alive, in the same way that tarantulas are killed by tarantula hawks. As suspects keep dying, the Inspector directs his attention to a spa all the victims had a connection with...