Springtime is for Swarms

A swarm cluster in a cherry tree

One of the most iconic and misunderstood behaviors of honeybees is the “swarm.” People fear the swarm – it conjures up thoughts of an unstoppable venomous aerial assault – and yet ironically it is the most friendly and tame way to encounter honeybees! Catching swarms is one of the most fun and exciting things about beekeeping, and is often the way that new beekeepers get started. My late grandfather started keeping bees when he caught a swarm in a cardboard box in downtown San Francisco. A swarm was how I got started as well. Until recently, I have only caught swarms and have never seen one leave a hive. To continue my National Pollinators Week series, I’m going to tell you all about swarms – including the biggest swarm I have ever seen, which came right out of one of my own hives.
In the springtime while flowers are blooming and bee hives thriving, worker bees get the itch to swarm. It often happens on very warm days after a cold spell in April to July, but sometimes as late as August or September! The earlier the swarm, the better. This is because it gives the bees more time to build up their new hive to produce honey, or make it through the winter. There’s a saying that goes,

A swarm in May
Is worth a load of hay.
A swarm in June
Is worth a silver spoon.
A swarm in July
Isn’t worth a fly.

So why do bees swarm?

The life cycle of a swarm

A swarm before it entered my apartment building. Click to zoom.

Honeybees swarm as a way to start new colonies from successful ones. Strong hives with an excess of bees are very prone to swarms. The worker bees sense the growth and crowding in the hive, and start building special queen cell cups on the bottom of the combs in the hive. The queen will lay eggs in these, and the workers feed them a special diet of royal jelly – a secretion from the glands in their cheeks. In just over a couple weeks, they will emerge ready to mate and take over the reproduction in the hive. But before this happens the old queen will leave – and take a cloud of worker bees with her. This behavior is called swarming, and is how new colonies are started.
First, the workers engorge themselves with honey to provide energy for the trip and to start building their new nest. When a swarm of bees leaves the hive, it makes a lot of noise and floats up into the air. Their first destination is the branch of a tree – and sometimes a house or a fence. The queen lands on the branch, and the workers cluster around her, making a very characteristic ball of bees.  During this time, they are looking for a new home. They may stay on the branch for a matter of hours to a few days while they search.
The swarm entering the apartment building

Honeybees prefer to nest in cavities, such as a hole in a tree, or inside a hive box provided by a beekeeper. They can also move into the eaves, attics, and walls of houses and barns or old tractor fuel tanks sitting on a farm. The swarm cluster does not want to stay on the branch, so it will send out scout bees that search for good nest locations, as well as foragers to gather nectar and water for the cluster while they wait.
The scout bees return to the cluster and use the same dance they use to tell each other how to find flowers, until the swarm agrees on one location. Then a few bees run across the cluster signalling to their sisters to warm up their wings and in an instant the cluster vaporizes into a cloud of bees again, following a handful of leaders that know where to go. Not every bee knows where they are headed, so the swarm itself is an amazing phenomenon of collective behavior!
Fanning bees

When the swarm reaches its new home, they will quickly go in. The first bees to arrive will point toward the entrance and start fanning the air with their wings. They are releasing a “hive” pheromone that tells the other bees that this is where they are going to live. Once the queen enters, the rest of the bees rapidly follow her scent. I once witnessed a bee swarm move into the wall of my apartment building in Davis, and I got to see this natural phenomenon in-action. I also recorded the audio. What you are hearing here is the loud characteristic buzz of a swarm.

If a swarm cluster cannot find a suitable home, they may end up building a nest on the branch. Honey-filled bees start producing wax, and after a few days they will just start building combs right where they are. Hives have been known to live on exposed branches, but they are susceptible to the weather and I have only seen them make it through the winter in locations with mild winters.

If you see a swarm

If you see a cluster of bees like above or a swarm at your home, do not be alarmed or reach for a can of insect killer. Honeybees defend their hive, but when they are swarming there is no hive to defend. Since they are also full of honey they are very docile. While you can still get stung by an errant bee in a swarm, overall they are the most friendly they will ever be. If you are allergic to bee stings, it is best to stay away and call someone else who can help. When the news media discusses swarms attacking people, they are actually talking about aggressive hives defending themselves – not swarms.

If you see a swarm you should find yourself a beekeeper, who will often remove the bees for free, or grab a box and start keeping bees! I once went on a swarm call with my grandfather and the homeowners sprayed the bees with bug spray before we arrived. It was a sad sight, and the homeowners got an earful from him. If, however you see an established nest of insects, try to identify them as honeybees, bumble bees, or wasps before taking any specific action.

A large free-hanging bee hive in front of Mrak Hall, UC Davis (2006).

There are many different ways you can find a beekeeper who will take a swarm off your hands. They are, after all, free bees! People who see swarms of bees usually call pest control, the local police or fire department, and the offices of local entomologists. Many also use Google to find out what to do. Any one of these routes can get you in touch with a beekeeper who can collect the bees – and I get a good handful of calls forwarded to me in Madison each year.
When I get a swarm call on my cell phone, the first thing I ask is what the person on the other end of the line sees, but even then it can be difficult to communicate over the phone. If they see a cluster of bees on a branch, that’s a pretty unambiguous sign, and I try to get there as quick as I can to catch it. But if it sounds like an established hive of some sort, it can be any number of different species. Since most people have cameras on their cell phones, I ask for a picture so I can make a positive ID. I’ve come to one too many “swarm” calls to find a paper wasp nest staring back at me. These are more active in the fall, and late summer calls usually turn out to be wasps. If you see these, reach for the can of spray.
Sometimes the swarms turn out instead to be established honeybee hives in the walls of a building. And since I’ve been in Wisconsin, I have received a number of bumblebee calls. Established hives present a different sort of challenge to remove, and I’ll discuss these in an upcoming post.

Swarm catching

Shaking a swarm into a box

Catching a swarm is very exciting, and is a rite of passage for every beekeeper. It is often how people first get into beekeeping,  like my grandfather and I both did. All you need is a suitable box to contain them, and you simply shake or brush them into the box. (My grandfather sometimes just placed the branch on the hive and let them crawl in.) The bees will readily recognize a suitable home, and begin fanning the entrance to the hive. Once the queen and her smell is inside, the bees still flying will learn the new location and move in.
It is exciting to have thousands of bees flying all around you, loudly buzzing, yet practically harmless. Swarms can often be collected without any protection from stings because of this. Imagine bees flying all around you, landing on your arms and shoulders, and you can feel the vibrations of thousands of pairs of wings, all while you are brushing or shaking them off of a tree and into a box which you will get to take home and keep! It is exciting enough with all the action, but the free-bees are also nice. Even my wife Ariela, who doesn’t like to work with the bees in the hives, loves catching swarms.
Trimming the cherry branches

While you can shake bees into any box you have around, the best place to keep them is a hive with removable frames that the bees build their combs on. This allows you to open and manipulate the hive to inspect it for problems such as pests and disease. In most states (if not all) this is a legal requirement. So by all means catch the swarm in any box you have, but transfer them to a proper hive when you get home!
Sometimes catching a swarm can be challenging. The tree branch can be high off the ground, for instance. In this case, I use a ladder to get up to the swarm, and then I tie ropes onto the branch, looped over a branch above it. Next, I cut the branch on either side of the swarm with a saw. Now I can just lower the branch to the ground and shake the bees into the box. If the branch is light, I can just hold it in my hand with no need for rope. But not every swarm is accessible. The City of Madison once called me about a swarm that was 30 feet off the ground above a busy multi-lane intersection. I said unless they had a cherry-picker they could bring there for me and stop traffic, I’ll pass. Hopefully the bees found a good home on their own!

When your hive swarms

The more bees you have in each hive, the more honey you can get. But at the same time, more bees means that you can lose some of them in a swarm due to overcrowding. If you are a beekeeper and you want to get honey – you will want to prevent swarming if your hives are strong. You can do things like cutting queen cells, expanding the hives and rearranging the boxes, and “splitting” them into two hives to make new hives and reduce their numbers.
However, even the most organized swarm-prevention strategy can be foiled by the bees themselves. This year, I had one extremely strong hive, a “survivor” hive that made it through two winters in Wisconsin, and came out of the mild winter of 2011-2012 doing particularly well. I expanded the hive again and again, adding more brood chambers and honey supers, and cutting queen cells every week. But they caught on, and decided to swarm anyway – before their new queen cells were mature. Ariela and I were having breakfast overlooking the back yard on a Sunday morning, and I noticed extra activity at the hive – more than you would expect in the morning. I was talking to my Dad on the phone when I put my ear to the window screen and heard the loud buzzing, and remarked, “I think our bees are swarming.” “Bye!” – Yelled my Dad.

The swarm began to settle next to the pine tree

This was the first time I have seen a swarm actually leave a hive, and it was quite amazing. Our sunny back yard was now home to a growing tornado of bees stretching up a hundred feet off the ground, while I frantically put on my suit and got a box ready. Ariela watched the cloud while I prepared to run after them – or race down the road in the truck if need be. The cloud started to gather next to a tall pine tree in our neighbor’s yard, and I readied myself to climb it armed with ropes and a saw – but there was no need. The cloud slowly settled toward the ground, right over the fence. I brought the box over the fence to find bees sitting on the leaves of every plant, with a thick cloud ten feet off the ground. While I snapped photos, they started to land on a low branch of the pine tree, and in a minute formed a large cluster with the majority of the bees still in the air. This was a huge swarm! I ran the camera back to Ariela – I would rather not risk losing these bees for a few more photos.
Already a large cluster!

I opened the box, grabbed an empty frame, and brushed bees from the cluster into the frame. Usually this is a slow process of bringing bees to the box frame by frame. But there were so many bees I was literally pouring them in. After a few brush strokes I looked down and saw the box completely covered with fanning bees – it was not big enough! This was the largest swarm I have ever caught. I had to grab another deep brood box, get some frames ready to place inside, and continue with the operation. When the bees were inside, I closed up the top of the box, and started to tie the box together to carry it later. Typical swarms take a while to move into their new home because they get accustomed to the tree branch. When I finished tying up the boxes, there were almost no bees in the air anymore – they were all inside or sitting on the entrance. I carried the double box over the fence and put it on the hive table, just 5 feet away from their old home. The entire affair took just an hour.
Brushing the bees from the branch

I hope these pictures capture some of the excitement that swarms can bring. It was a relief to recapture these bees, which are now already a strong 2-box colony, producing bees and gathering honey. The hive they came out of has rapidly recovered its numbers. I inspected the hive, and found many young queen cells. I discovered that rather than wait for me to cut the queen cells again, they swarmed early! Clever girls. By now, the new queen has emerged, mated, and taken over egg-laying responsibilities. Once I have confirmed this, I’ll go back to my swarm control routine. Although swarms are exciting to witness and to catch, I’m hoping for a huge crop of honey from this hive. White clover is in bloom and I want the bees to take full advantage of this hot Madison June.


  1. Wow… so interesting. It’s winter in NZ so no bees around but in the warmer weather we get big dozy gorgeous bumble bees. Not sure if they swarm.. but it would be amazing to see.

  2. Bumblebees have a different life cycle. In the fall, young queens leave the nest and find places to overwinter until the spring, where they start up their own colonies. So you won’t find them swarming like honeybees do. Honeybees are where the action is! 🙂

  3. I remember seeing a David Attenborough documentary showing the life of a bumble bee. Quite ruthless and violent towards one another.
    We’re really lucky in NZ to have hard working bees that make many kinds of remarkable honey. So many flavours from the native plants, and of course the famous special Manuka honey. Such good stuff.

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