Archetypal Permanence

Since the book spans thousands of years, documenting the evolution of the spiders could have turned boring pretty fast. But the spider history arc is told using the same archetypal characters. We follow Portia, the adventurous spider, Bianca, the heretic or Fabian, the only male character. 

Using the same names for the spider heroes is more than a trick. It makes sense in the lore of the book because the spiders evolved by passing their innovation (called the Understanding) to their offsprings. So there is a genetical timeline continuation to the main characters ... over thousands of years.