Sometimes, queens die. It could be old age, it could be she got injured during an inspection. It's hard to say what happened to her. If a queen is failing, meaning she isn't laying the amount of eggs the colony would like to see, the hive will make a unified decision to replace her. They use one or a few of her eggs she's laid to create a supercedure or emergency queen cell. As long as there are some viable eggs, that is. But, sometimes she doesn't lay eggs and then dies and the hive is queenless with no replacement potential. You have 2 options. You can buy a mated queen, but those are kind of pricey with shipping. Or, you can steal a frame of eggs from another hive and they'll make a queen from that frame. I'm telling you this because I wanted to explain what I did back on 03/07. I stole a frame of eggs and gave it to a queenless hive with no eggs. I couldn't tell at that time that it was mostly drone eggs. I know now because it was a bunch of drone capped brood when I checked on it on 03/25. Drone brood is puffier, almost like kix cereal. They can't make a queen out of an unfertilized egg, which is what drones are. So, I gave it another frame on 03/25 and on 04/01 I found 2 queen cells! Yay! Now, my next check will be on 04/15 to see if there are eggs. If I see eggs on 04/15 that means the virgin queen was born, took her mating flight and made it back successfully mated and is now laying eggs!! I will NOT open the box until then because I could disrupt that whole process by disturbing the hive. Look below at the drone brood and how it sticks up higher than the worker brood. That's how you tell if males or females (workers) are going to be born.