Mmm, ribs! Now where's my bbq sauce?

The front of a Monarch caterpillar looks very much like the back. That gives the caterpillar a 50-50 chance of decoying a predator into attacking the wrong end -- if any are foolhardy enough to ignore the bold black & yellow pattern which advertises the fact that it is poisonous. It concentrates noxious compounds from the milkweed -- the milkweed makes these compounds to discourage things from munching on it, & the caterpillar has evolved the ability to not only evade the milkweed's defenses, but turn them to its own advantage.

This is a big guy (maybe ~3", or ~8 cm), probably about to pupate soon.

Rick gets credit for spotting these caterpillars. I checked that milkweed patch every time I visited, & just when I had finally given up...