There are a lot of questions about how to acquire bees. We'll cover the options here.
First we have to understand why swarming occurs. Swarming is a honeybee colony's natural desire to procreate. Just as a plant will cast off seeds each year, beehives tend to want to cast off swarms. This happens when the colony feels it is strong enough to surrender roughly half it's population, and when they feel the chances of survival for both the remaining colony and the swarm have the best chance of survival. So it makes sense that the spring is a typical time to expect swarms.
I reiterate the "want" to swarm. Some colonies are more prone to swarming than others. But in general honeybee colonies want to swarm in the spring. It's ingrained in their DNA. Just like how pretty well every other living thing on earth feels a need to procreate. Turns out there is some truth to the old line about the birds and the bees!
When a beehive decides it wants to swarm, the first order of business is to get some queen cells ready. This is because when the swarm leaves, they are going to take the existing queen with them. This means that the remaining colony needs a queen as well to replace her. The colony will seek out ideal larva and begin raising queen cells. The existing queen allows this, as she has basically been informed of the plan and she knows those queens will not be a threat to her. Once the queen cells are capped, there are only a few days until they will emerge as fully developed virgin queens. A few days prior to swarming, some queens will stop laying eggs, and their abdomen will actually shrink a bit so it is easier for her to fly. Before leaving, the swarm will load on up about as much honey as they can carry. They'll need this for food along the journey, and to have the energy to quickly build combs once in a new spot.
Now it's time to go. The queen will gather up her supporters 40-60% of the colony and they will exit. Typically they will pour out in grand fashion and light in the air in a cloud. This cloud will settle nearby to gather up, and then send out scouts looking for a new home. A swarm may remain in place as little as a few seconds, to a few days, depending on weather and how successful the scouts are at finding a good spot. Once an acceptable location is found, the swarm will again take to the air and move off to their new home. A swarm may move several times along the way until the find a new place, either because of a disturbance or just because. And, a swarm may move into a space, and then decide it's not suitable after all and move back out.
A special note on swarms is that they do tend to be more docile than an established colony. It makes sense. When you think about the attitude of a colony, folks often interchange aggression with defensiveness. But the two are very different. Most beehives tend to be a little defensive of their brood. But in general don't bother you unless you bother them. Swarms on the other hand have no reason to be defensive. They have no home, no food, and no babies to defend. The only real risk of stings when dealing with swarms would be if a bee gets frustrated from you messing with them too much, or gets worked up in the confusion of being shaken into a box and tossed around. I often capture swarms with no suit and even no smoke necessary. After all, they are looking for a home, and you just gave them one. If anything they should thank you!
So you want to catch a swarm huh? Sounds easy enough. I try to make it look easy. Let's cover the options for how to benefit from catching swarms.
I call it "chasing" swarms, because that's really what you are doing. Someone calls ans says they spotted a swarm in a tree. So you drop everything you are doing to go after them. You run to the house to collect your gear and then an hour across town (this is Houston, that's not that far). You show up and guess what, no bees. Are you in the wrong spot? Nope, you were just too slow.
Now, that's a worst case scenario. But the point being, chasing swarms can be very time consuming, and may not always get there in time. In addition, there is always the chance (just like any other bee move) that you get them home, and then they leave again the next day. The first swarm I ever chased took me nearly 1.5 hrs from the house. It was 2 hours on location to get them out of the top of a small tree, and then an hour and half home. Oh, it was like 60 degrees and misty rain. I found the queen, caged her and got them home. Released her (rookie) and gave them a quart of sugar water. The next day I got home from work to find the feeder empty, and the box! They left me!
Lessons learned here. To chase swarms, you have to be ready to go on a moment's notice. Not all that easy when you have a full time job, a wife and three kids at home. The other catch is that folks need to know you are looking, so they know to call you. In three years now, I've never spotted a swarm outside my own yard. It's always been a call from someone else to let me know.
Chasing swarms can be fun and successful. But it's not my preferred method to catch them.
When it comes to trapping swarms, this is the way to go. Keep in mind that when a swarm is moving, they are looking for a place to set up a new home. By placing out a series of swarm "traps" in the area, they just might move in for you. No running all over town. No ducking work early.
Trapping swarms is simple enough, in theory. Provide them a shelter they like, and they'll move in. If you build it, they will come. Right? Well, maybe. There are a few things to consider. They want a specific size of box to move into. Something big enough they can grow into, but small enough they can defend it. And putting it near food and water is a good bet. There is literature available out there on how to optimize swarm trap design and location. There are also lures you can buy to up your chances. On the note of lures, I've had mixed results. Most folks recommend just lemongrass oil (LGO) as it mimics the bees' orienting pheromone. I've had no success with just LGO, but do use it to draw bees to the box on removals with success. I've also used it to attract a swarm to my pocket once (on accident) as I had a bottle in there the day before that leaked! I've had better luck with designed swarm lures. I sprayed some on a tree as a test, and three days later had a 1.5 lb swarm fixed tightly to that exact spot! I ran them into a box and caught the queen. Released her a couple days later and they bailed on me. DOH!
OK, so in general, you want a box about the size of 10 frame deep to catch most sized swarms. Too small of a box (5 frame deep) and bigger swarms may not settle. Too big of a box and they may not feel secure. In fact I like to use just that, a 10 frame deep. I set it up with frames and starter strips, so if a swarm moves in they can go right to building, and I don't have to cut them out of the trap later. The "swarm traps" I've seen sold online that are a cardboard box or a paper fiber cone shape make no sense to me. What a rip off, and what a pain in the butt!
Put it in a discrete location near forage and water. I say discrete, because you don't want a possible thief or vandal to find it and destroy it. Or track it when you aren't and steal it when a swarm comes in. Once the boxes are up, bait as you wish, and then once a week or so just walk your trap line to see what you got. If you spot that a swarm has moved in, come back after dark and carefully take down the box, in tact, and relocated it to your apiary. Offer them sugar water, as they need the support to build up quickly.
Check in a week or so later (or a day if you just can't wait) to see how things are going. I've had a 2-3 lb swarm fill out a 10 frame deep in just 2 weeks if fed well. Don't let them get ahead of you! If they settle in, then you are pretty well done. Success! Just make sure you replace that trap so you can catch more!