Make cake according to box instructions.

Preheat oven to 350 degrees F.

Divide batter into 3 bowls and add natural food colorings into each.

Pour batter into 3 6-in. cake pans and bake for 30 minutes or until toothpick comes out clean.

Remove and allow to cool for 10 minutes.

Whip icing and spread between each cake layer, top of cake and around all sides.

Use spatula to even icing out and transfer cake to fridge for 30 minutes and allow icing to harden.

Melt marshmallows in microwave and mash them between hands, slowly pulling apart to get strings.

Drape over cake and add plastic spiders for extra decoration.