Today a hive I split six weeks ago swarmed. This hive was queenless I till three weeks ago and they requeened themselves. The new queen was doing fine. Hive shows lots of capped and uncapped brood and fresh layer eggs. I inspected hive and it has zero swarm cells. This morning I find a small swarm the size of a grapefruit about 10 feet from the hive. I was feeding and they had a pollen patty. I was able to capture the swarm and I placed them in a temporary box. I have two questions. One. Why would they swarm if they had plenty of space and zero queen cells. And two. Is it possible to give them a week and put them back in with their original hive? There is not enough in numbers for them to survive the season.
How many bees in the hive that might have swarmed from? Are you sure the hive is queen less? I would look hard for queen or wait few days and look for eggs. In the mean time start a nuc with what you caught. Give them some comb and frame of brood if you can spare it and feed. See if they stay. Give it a little time to get it correct. If your hive still has queen use the nuc as queen bank and combine before winter. You can then decided what queen is better. Small swarms are sometimes bees that absconded not swarmed.
Are you sure the swarm is from your hive? I would put it in a nuc with some honey and brood and feed it like there is no tomorrow. Nothing lost if they don’t survive your winter but a free hive is not to be ignored.