But more seriously, it's not often you see some Caterpie art, and I can certainly say that I've never seen anything like this! First of all, the style of drawing and shading works really well, giving a good indication of a light source, blah blah blah...
Now - onto the design, which is pure genius! The claws and spiky tail fit well - they're not too over-the-top. The eyes might seem a little bit dull, and the mandibles are a little skew - but I'm just nitpicking now. I kinda feel they add to the scariness, and ferociousness of the design anyway.
I also really like the way you've used a background colour that is the same as it's mouth, as well as being [almost] a complimentary colour - it fits really beautifully!
This is my first critique, so I'm not going to go too in-depth here, but I think this is a very interesting approach to Caterpie. Throw in the fact that you see almost no good Caterpie art, and you come out with an amazingly unique piece.
I love how you added the pincers on the back of its tail; it definitely adds to the freaky feel. The only things I can pick at, well, at all are the feelers on top of its head and its "arms" (sorry, don't know the correct term here). The right (Caterpie's right) feeler is a bit askew and shorter than the other, even if Caterpie's turned to the right. With its "limbs," the left ones seem to be a bit askew as well. Really, though, I'm just nitpicking; these little things only add to its disturbing feel.
This is an amazing piece, and the fact that you were able to turn a simple Caterpie into a monstrosity makes the piece all the more stunning.
This looks sort of like what I imagined a monster to look like in GammaWorld when I played it with a club I used to be in. It really brings back memories, it doesn't look quite like a caterpi should though. I always thought them to be cute, this is just plain scary looking.