Arachnids are a class of chelicerata arthropods from which more than 102,000 species have been described. Includes well-known forms such as spiders, ticks and other mites, or scorpions.
Arachnophobia is the disgust or irrational phobia of spiders. It is one of the most common phobias, and possibly the most widespread animal phobia.
Sometimes, sunset can be viewed as "romantic". If the author wants to build a relationship the sunset is used as a pathetic fallacy (when the weather matches the mood). The sunset refers to love which will overall build their relationship.