This spiky little creature is an early instar Polyphemus moth caterpillar. The head is at the right side and is tucked under so it can't be seen. To see the mature instar caterpillar (quite different): http://www.pbase.com/laroseforest/image/157185163

To see the moth it will become: http://www.pbase.com/laroseforest/image/156495801