This little creature is the larva of the green tortoise beetle (next photo). Like all tortoise beetles, it is fecally protected. That is, it carries a shield made of fecal matter, over its back. The shield is hinged at the back and can be lifted or lowered. It is probably to protect the larva from becoming a snack. Many beetle species seem to have this form of protection in the larval stage. It is on a canada thistle with which this beetle is closely associated. In fact it is often called the thistle tortoise beetle. By the way, the head is on the left and you can just about see it as it grazes on the thistle leaf.