In a large bowl cream together butter and vanilla. Slowly blend in the sugar, one cup at a time beating well after each addition. I love using my Kitchenaid mixer for this! Beat in the milk and continue mixing until light and fluffy. You may need to add more sugar or milk until you find the right consistency, this varies every time I do the recipe.
Mix in green food coloring until you reach the desired color. If you are not going to use the frosting right away keep covered until you are ready to do so. Stir in the vanilla bean seeds just before using.
Pipe frosting using piping bag or Ziploc bag with corner cut off) on the bottom of one Oreo (not covered in chocolate side), go around the edge of the cookie two times, so that the cookie has 2 layers of frosting. Then top the frosting with another Oreo, bottom side directly on the frosting, while making sure that the eyes line up. Slightly push the Oreos together, to make sure that they hold together.
Look at pictures above recipe card if you need help with decorating. Place on wax paper, and repeat with remaining Oreos and frosting.
Cut Twizzlers into strips, 6 for each spider. Insert into the frosting, 3 on each side.
Let them set, then serve and enjoy! They can be wrapped individually to give as a treat.