This is a known bug. It consumes lots of beans, but other than that, it's relatively harmless.
bugguide.net/node/view/349515
It's called a shield bug in the vernacular, or Megacopta Cribaria. I think it looks pretty cool, as known bugs go.
Any other neat "known bugs"?
(NB4 'OMG BT UR PUNZ R TERRIBAD')