i thinking killing a spider is bad luck.
spiders symbolizes different things: creativity (the way the spin webs); your desires your in waking life; bugs represent irritations, hidden emotions
i think there is a book called animal wise that discuss the symbolism behind seeing animals frequently. I plan on getting that book, bc I am always seeing Hawks. In HS it was squirrels. I think animals can denote and send messages just by seeing them often there is something you are meant to be aware of.
the dream could just be a playback of what you saw in reality.
Knix--You are a very gifted interpreter of dreams!
Just went to look [online] for the book mentioned above as I've been seeing Cardinals a lot lately.
However, based on a review on Amazon
http://www.amazon.com/review/R3K5FE43U5CFS3, it may not help with birds and mammals we see day to day in North American. For instance, according to the reviewer squirrels and cardinals are not included. Though this book and another cited in the review was said to cover insects, arachnids, reptiles and amphibians.