We had five monarch caterpillars on the butterfly weed. Yesterday the smallest of the five formed a chrysalis. It only took a few hours but over 24 hours earlier the caterpillar had positioned itself into a J hook shape while suspended from a short thread attached to the underside of a leaf. I read it takes about 10 days for the butterfly to emerge. We have hunted and hunted for the other four caterpillars or chrysalises to no avail.
It is so amazing how a caterpillar transforms itself.