So I thought it would be easy to find black paper cups this time of year, but no. Every store just sold the big plastic ones with ridges. Then I looked for any solid-color paper cups. Still nothing. So I ended up buying some monster cups from the birthday party section at Target and painted them black. It took two coats of paint, but went fairly quickly.
Fun Fact: Spiders have pale blue blood!
10-18-12 UPDATE: We made these again this year (although I found and bought black paper cups!) but used colored glitter pipe cleaners. I love the added color!