Bake the cupcakes according to the directions on the box EXCEPT.....when filling the cupcake liners; fill halfway with the batter then place a cookie in the liner and finish filling with the batter.
Allow cupcakes to cool completely.
Start working on this while cupcakes are baking and cooling:
Place the black candy chips in the corner of zippered sandwich bag and heat in the microwave for 45 seconds. Gently massage to ensure candy is melted and smooth. Clip a tiny piece off the corner of the bag to pipe.
Make a black dot in the center of each M&M to look like an eye.
Gently twist apart each Oreo. Cut each candy string into 4 equal parts and press each piece into the icing of the cookie to make 8 legs.
Pipe a little melted candy to act as glue and put the top back on the cookie.
Pipe a little melted candy on the top of the cookie to glue eyes in place and allow to cool and set.
In a large bowl, cream the butter and vanilla. Slowly add in the powdered sugar, and milk (as needed) until everything is incorporated and frosting is the right consistency.
Beat for 5 minutes to make sure it is fluffy.
Ice cupcakes then decorate tops with the spiders.