Final answer:
The spell used to blast away spiders in Harry Potter is Arania Exumai, and the text provided for context is a poetic interpretation of a spider in nature, symbolizing innocence and malice.
Step-by-step explanation:
The spell used to blast away spiders in the fictional context, specifically in the Harry Potter series, is Arania Exumai. However, this question also engages with poetic interpretation, as it somewhat relates to the analysis of a poem that features a spider.
The provided passages draw attention to the contrast between innocence and malice in nature, particularly focusing on a white spider poised on a white flower with a moth, symbolizing themes of death and design. The imagery used creates a scene that is simultaneously natural and ominous, suggesting a design in nature that can be dark and complex.