What‘s a pandora moth?

I caught the tail end of the Pandora moth outbreak on a recent visit to Bend, Oregon. I lived in Bend for almost five years without seeing a single Pandora moth. This summer I saw thousands littering the streets and parking lots, mostly dead or dying. When I asked friends about the moths, I got shrugs. Nobody really knew what they were or where they came from.  I was fascinated. Was this a foreign invader, a ravenous beast that would defoliate the state? Would its larvae overwhelm the town come spring?