When playing the last mission of the campaign my Hive was attacked by some flyers, and was reduced to red. I finished off the attackers and thought my buildings would heal back up, but when the next attack came in a few minutes later my building was still bleeding and in red. It just barely survived this time, so I parked a queen next to it for some healing, but when the next attack came in it didn't look like it had healed at all, and the queen had 100+ energy. Manually transfusing the building seemed to work, but it would take a ton of queens to make this viable, so I think I must be missing something.
Do Zerg buildings heal? Is there a way to make a queen auto-transfuse a building, in case I want to park one next to my Hive?