I wouldn't recommend refrigeration, as that will promote condensation when you open the camera to shake out the chilled critter.
I'd suggest you let the poor thing expire, then open the camera body and thoroughly work over the interior with a rocket blaster or similar. Keep the open lens mount pointed down, and perhaps place a sheet of dark paper or the like underneath so that you can confirm you got the wee beastie out of the camera body.
As for how it got in, Leadbelly, I think you guessed right about leaving the camera open too long during a lens change. The K10D's body sealing includes the LCD's external protective screen, IIRC, so the path to the LCD itself was most likely through the open mirror/sensor box during the lens change.
Good luck!