I agree with Maljonic that a lot of it depends on how you personally feel about the things in your dreams. I think that the snake attacking with you might mean that something is bothering you, and the fact that you can't find the spider could mean that you are having trouble finding out what is wrong or what you have to do about it.

The second dream about the taxi also brings to mind the theme of being lost. In the first dream, you've lost the spider, in the second you are lost, in space as well as in time.
Maybe the feeling of being in the 1900's specifically came from a book you read or a film you saw, maybe even something you read or saw a long time ago.