I found them on the Lilikoi (passion fruit) plant. For many days I've been wondering why the leaves were full of holes and assumed it was my black thumb in action again, but upon close inspection I spotted a small prickly caterpillar munching a stalk. Then I found two and three and now four of these spiny fellas.
My web search identified these as Gulf Fritillaries or passion butterflies. You can read more about them here and see them as butterflies. This is the first time I've ever seen caterpillars such as these, but according to the article, these butterflies are quite abundant on the islands.
I hope the passion fruit vine will have enough leaves to feed these hungry hungry caterpillars because I'm excited to see these monsters transform into beautiful butterflies.