Combine leaf green and lemon yellow icing colors for green shown. In advance, make webs. Tape wide web pattern on the outside of large flower former; cover pattern with waxed paper and tape in place. Tape narrow web pattern to cake board; cover pattern with waxed paper and tape in place. Use tip 5 and black royal icing to outline web patterns. Make 4 of each size web and extras to allow for breakage. Let all webs dry overnight. Carefully remove from waxed paper.
Bake and cool cupcakes. Ice smooth in yellow buttercream with spatula. Using orange, violet and green buttercream icing and tip 12, pipe spider body. Pipe tip 10 head. Use tip 3 and white buttercream to pipe whites of eyes and tip 2 and black icing to pipe pupils. Pipe tip 4 legs.
Position cupcakes on stand. Place wide webs on lower level of stand and narrow webs on top level of stand.