What´s the meaning of......

I think a story like this isn't supposed to be exactly explainable. I think the writer deliberately puts loose associations in our mind. As I remember it, in the movie it is the last story Molina tells, and in the book it is a fabrication of the drugged mind of Valentine that has the shape of the sort of stories Molina told. Molina said he always identified with the female lead of the story, so Molina is the spider woman in that last story, for sure. The weaving of a web I associate with the stories Molina told, capturing himself in guilt and capturing Valentine in betrayel. All the stories Molina told where around the same kind of motives, and in the end Molina fulfills his own leadpart in a story of that nature, becoming the spider woman (becoming a heroin in a story).

While some some think that "Spider Woman" is a deeper metaphor, the answer is actually quite literal. When Raul Julia sprayed diarhea all over the jail cell, it was in the shape of a spider.