Do ye not understand that we are worms,
Born to bring forth the angelic butterfly
That flieth unto judgment without screen?
I don’t know why these particular caterpillars are leaving the relative safety of the plants (which are naturally toxic to their predators) to take to the stucco rooflines, but they are. They carry the nectar toxins within their bodies, so they continue to be repellent to predators, even when away from the plants. I did a quickie wiki background check for their lifespan/cycle. The eggs hatch within four days. The worms eat ravenously and grow for two weeks. The chrysalides develop for two weeks. The butterflies live up to 6 weeks, except for the last “generation” of the summer, which live up to 8 months and migrate to/from warmer climates.