What was that bizarre balloon-spangled creature?
It’s the larva of a Theope butterfly in the family Riodinidae. Here is the full photo, from Panama:

An infinite number of highly valuable Myrmecos Points(™) go to commentator JasonC, who not only identified the larva but researched the function of the balloons.
I was leaning toward something extraterrestrial.
Gorgeous shot, Alex! And what an intriguing beast it is.
Great Job Jason! I love you!