In the world of dreams the rules of reality do not necessarily apply. Each dream is unique and it's a direct link to the soul and spirit. Psychology provides its own theories on what dreams mean, but so did tradition and the study of dreams for thousands of years before any relevant science had developed.
Dream Meanings - Spider
If you are cleaning your house of spiders then something good will happen to you. If, however, you dream of spiders or their webs then there will be difficulties in your life.