There are biological limits to the size insects can grow due to there respiratory system. Simply put, it's the square cube law. That's why back in prehistory when there was more oxygen in the atmosphere that insects were larger. What I'm trying to say in my incoherent way is, those giant spider monsters should be impossible based on Earth biology and physics. So they should simply be a case of parallel evolution and an Earth solution should not have worked on them as they are not real earth spiders, they just look like them.