If this creature, which is straight out of bizarro-land, isn't a bird dropping mimic, nothing is. No one in their right mind would attempt to eat it. If you can't even tell what it is - forgiven. I wouldn't have known either, not so long ago. We're looking at a female Bolas Spider,Mastophora hutchinsoni. During the day, she'll rest motionless and out in plain sight on the upper surface of a leaf, relying on her unsavory appearance to discourage would-be predators.
At night, the spider stirs to action and employs one of the wildest hunting strategies of any animal, spider or otherwise. Read about the Bolas Spider's amazing predatory tactics on Julie Zickefoose's blog, HERE.
David Wagner pointed this one out to me on another field trip this summer, and it stumped me. This is an early instar of the fabled Hickory Horned Devil caterpillar, and I had no clue that these cats were bird dropping mimics in their early stages. Yet here it is, and it's doing everything that a good bird dropping mimic does.