I was inspired by this site to make my own Caterpillar Birthday Cake for my daughter's first birthday party. It was actually really easy, but looks complicated and received a ton of compliments.
I used the Wilton Sports Ball Pan, but you could easily use any oven-proof bowl that doesn't have a flat bottom. Using the Wilton set, one cake mix makes 2 bowls, so I used three mixes. You could certainly use a scratch recipe (times 3), but mixes work generally work for me.
Because the cakes are so thick, they take awhile to bake...around 50-60 minutes if I remember correctly. The instructions for the Wilton set (available online) could be adapted for a different bowl of similar size/shape.
After taking the cakes out of the oven, I let them cool for about 20 minutes, then used a bread knife to trim the excess where the cake rose above the pan, then turned the cakes out onto a cooling rack (or, in my case, paper plates). Since the cakes took so long to bake, I baked most of them on Thursday and the last 2 on Friday, and wrapped them well and stored them on the counter until I iced them on Saturday morning (party was at noon on Saturday).
Then it was just a matter of covering a cardboard box (which I reinforced in the center with pieces of cardboard, because the cake was pretty heavy) with a plastic tablecloth (stapled), arranging the cakes (I cut templates out of paper plates first to get an idea of where I wanted to put the cakes), coloring the frosting, and slapping it on. Most people seem to do the star method, but I didn't have that sort of patience. I think it looked fine with the icing kind of swirled. I used gel food colors to get the vibrant colors, and a Dream Whip buttercream for the icing. The antenna were black pipe cleaners.