you shouldn't have that many spiders in your house , if you do its a sign of other bugs , and thats typically due to something wrong , either moisture trapped in attic / old insulation that is allowing them nest .. etc etc . find the source of WHY there is bugs.
The best way to be energy efficient. Is to fix whatever is constantly causing the humidity. Have you properly encapsulated the space? I've heard great things about Aprileaire. What unit's are you currently using?