Meet the caterpillar of the saddled prominent moth, Heterocampa guttivitta. This spectacular, bright green caterpillar is speckled with red spots, and has longitudinal yellow stripes, and a huge, flat, almond-shaped head with black, red, and yellow stripes. Apparently the defining characteristic here is the two red and yellow horns, or warts, at the back of the head (here’s a better example from bugguide, and below a closeup of the above individual showing off the horns).
The color patterns on the body are highly variable (and gorgeous), generally consisting of yellow and orange spots or patterns on the back, with one bold yellow stripe going along the abdomen. For some reason, this caterpillar enjoys going about with its “tail” in the air, as pictured above. This may encourage predators to attack the wrong end of the caterpillar.
I don’t have a photo of an adult saddled prominent moth (yet!), but bugguide does. They’re surprisingly boring and brownish grey for having such beautiful caterpillars.
This individual hasn’t yet grown/may never grow the bright red horns in (although you can see something that might be a bud), and has different patterning, including some lovely red blotches, a broad white stripe down the dorsal side, and candy-cane-striped legs. The black lines still differentiate it from other species of Heterocampa.