My favorite caterpillar! Pseudosphinx tetrio.I've only encountered these on St. Croix, but they range all the way from Brazil to the southern United States. They are HUGE. The one on my index finger is the smallest one I've seen yet. Amusingly, their heads and tails seem to stay about the same size.
They feed on trees of the Apocynaceae family... and they poop a LOT. There are some trees that grow over the top of the fence around the pool where we stayed, and the poolside was littered with caterpillar poop.
Some of my further observations -
Their tails move up and down with each body movement forward, which looks quite silly.
They do not like each other - when two caterpillars were brought close to each other, they would thrash around and try to bite each other.
Their true legs have some sharp claws!
They can not bite people, at least not enough to break the skin.
They can spit up some nasty smelling green liquid.
They smell a bit, rather like the plant they are eating.
I also encountered an adult moth - they are not nearly as flamboyant as the caterpillars.
I still can hardly believe such large colorful caterpillars exist, they're next on my list of plushies I need to make.