"They" say nucs don't swarm but whoever "they" are are wrong. Went into the Munly's hive today. Two deeps, six or seven frames of bees in each box. A little honey and a little pollen. Lots of capped brood and larva. The bees were doing a magnificent job of drawing out comb. Magnificent! Adding extra wax to the frames made a huge difference.
But there were about a dozen swarm cells. A couple of them were closed up and the rest were well on their way. The colony was not out of space in any way, shape, or form. We did not find the queen but there was lots of very young larva.
Once we found the first swarm cell we ended up shaking all the bees off of each and every frame into the brood box. We cut off every swarm cell and cup. There's no way one could find every swarm cell without shaking off all the bees first. If you miss even one, they will swarm.
This colony was not strong enough to survive if it had swarmed. We did the right thing. So we want you to be sure you check for swarm cells ASAP. Putting the top deep on it's side allows you to get a good look at the bottom of the frames where the swarm cells usually are. If you find even one, take action. If you need help and have a bee buddy, give that person a call. If you don't, call or email Claire (clairemoody503@gmail.com).
If this had been an overwintered hive the action to be taken would likely be a split or an artificial swarm: taking the queen and half the bees to a new location and letting the swarm cells mature.
With a nuc those are not good choices.