I got a call today right at 5:00 pm from a gentleman who had a very small swarm in his back yard on the ground. I grabbed a nuc box and got them inside in just a few minutes. I'm not sure if there's enough bees to even survive though. The total mass looked about the size of your fist. I've left the hive at his home for the evening to let the stragglers move in during the night. I also put in a frame feeder to give them a good meal. I hope to get several swarms this year along with the package bees I've already ordered.
Did you use a queen excluder as a means to keep the queen in the box? If not I would suggest showing up really early and put one on. Or you might find the bees gone.
a frame of brood will help keep them from leaving also plus give them a population boost, it is also a good thing to add a empty frame of drawn out comb also if you have one so the queen can start laying right-a-way.
Picked up the nuc tonight and brought it home. The bees are all safely inside and working on the comb. There's not a lot of them so I don't have too high of hope for thier survival though. The homeowner had hit the swarm twice with a garden hose to knock them off his home. Time will tell. Photos are at my smugmug site. Look at smugmug.com and do a search for Lenny Taylor (I can't do links yet.)