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Why do bees swarm?

From late April to July, honeybees are on the move. Swarming is a surprsing story of queens, dancing bees and an uncertain journey.

Why do bees swarm - A swarm of honeybees gathered on a fence post in front of a church - before moving to their new home
A honeybee swarm gathering on a fence post

More and more people keep honeybees. There are hives in city back gardens, on balconies and on roof tops. People have always kept them in the country and on allotments.

Wherever you live, you might see a swarm.

It's an amazing sight but a big swarm can be a bit alarming. It can be a real problem if they set up home in your home!

But, even if inconvenient to us, swarming is a natural thing. So, what exactly are the bees doing?


Honeybees live as part of a complex colony made up of thousands of individuals. At the summer peak, there are perhaps 60,000 workers (all female), a few thousand males and one queen.

Swarming is the way this colony reproduces - by dividing itself. Rather than our world of one male and one female getting together to make a child, think of an amoeba splitting itself into two.


To swarm, the colony needs to raise a second queen. At the same time, a small number of workers are scouting out new nest locations.

Even before the new queen emerges from her cell, the scout bees prompt the old queen and two thirds of the workforce to leave the hive.

There are thousands of them. They fly out in a swirling cloud and then gather their forces on a nearby fence or tree. Beekeepers call this cluster a bivouac.

A honeybee bivouac hanging in a tree - with a man hand placed next to it in order to show the size of the cluster -
A honeybee bivouac - hanging in a Cheltenham tree

The swarming bees form a dense mass. The queen is in the centre - kept safe and warm by the bees that surround her. This resting beard-shaped cluster is what most people imagine when they think of a swarm.

The bees may stay like this for a few hours or a few days because, next comes an amazing piece of animal behaviour.

Although the scout bees have identified some potential nest sites - the swarm doesn't actually have a final destination when it leaves the parent hive.

It's the job of each scout bee to convince her swarm mates that she has found the best place to set up home.

Each scout bee "advertises" the site she has found by dancing on the surface of the cluster. The dance recruits other bees to go and check out the advertised site. The dance also tells them its direction. The better the site, the more energtic the dance and the more bees are recruited to check it out. Over time, more and more bees will dance for the best site.

Eventually, one site will have more dancers than the others. This site will be the bee's new home.

With the help of many dancing scouts, the swarm of bees reach agreement on the best home for their new colony 

When they are ready to move on, the swarm flies like a swirling comet to the site they have chosen for the new nest site.

Before they left the parent colony, the swarming workers filled up on honey. They'll use it's energy to make beeswax - to build the comb that will make up their new home.

Back at base, the new queen stays to head up the old colony. So, one colony has become two! The bees have reproduced.


Bees swarm in the spring. Late April is the begining of swarming season. Spring flowers, rich in nectar and pollen, help a honeybee colony grow rapidly at this time of year.

When the weather is good, when there are lots of workers and plenty of honey, the colony will swarm.

They'll choose a warm day - leaving the hive around 11:00 to 4:00ish.

Some colonies can swarm as late as July but it's risky from a survival point of view.

A swarm in July may run out of time - it can't grow big enough or quickly enough to gather the stores it will need to survive the coming winter.


There are different schools of thought when it comes to swarms. Some beekeepers are happy for their bees to swarm. They say that it's a natural thing - which of course it is.

The more mainstream beekeeping view is that swarming is something that should be managed. This is our view. It's what we teach new beekeepers who come on our beekeeping courses.

Harry wearing bee suit ready to collect a swarm of bees hanging low down in a tree - the bees will drop into a box placed underneath them
Collecting a swarm of bees from a tree

We take this view because there are more and more beekeepers. These beekeepers are usually urban beekeepers - bees are not being kept in "natural" places or in "natural" densities. Honeybees are not in decline.

There are four reasons for beekeepers to manage honeybee swarms:

  1. Good manners - a beekeeper may love their bees but their neighbours probably won't. Every year I get calls to retrieve swarms from inconvenient places - such as inside a boiler!

  2. Loss of bees - reproduction is a strong drive. Bees will swarm as many times as they can. After the first swarm (called the prime swarm) there may be others (called a cast swarm). Each time, the size of the parent colony will roughly halve. Quite soon the original colony will be too small to survive. The bees will have done what they need to do, but the beekeeper's career will be a short one.

  3. Loss of honey - not every beekeeper keeps bees for honey but lots do. A swarm is a double whammy for honey production. A swarm takes honey with it - so there is less for the beekeeper. The swarm is made up of thousands of workers. They are part of the workforce that's needed by the colony to make honey in the summer. They've just flown away over the fence.

  4. Impact on biodiversity - honeybees are foragers par excellence. They gather vast quantities of nectar and pollen from many different flower sources. There is an unnessesary impact on bumblebees and solitary bees if honeybee swarms hoover up all their resources.

Swarm management is an important part of beekeeping. A beekeeper can learn to anticipate and take simple steps to avert it - giving the bees more space is top of the list - or, go with the flow, and manage it.

There are lots of ways to do it. All of them work with the bees natural desire to divide - just encouraging them to do so without leaving the apiary.


Generally, swarming bees will be "passing through". If they do come to rest in a tree etc they are likely in their bivouac. They'll probably move on within a few hours or a day.

The bees are focused on getting to their new home. They are unlikely to sting you - just be cautious and keep out of their way.

Especially if they are near a foot path for instance or in a building, you may want to contact your local Bee Keeping Association. Every association has a swarm collector who can help.

Follow this link to the British Beekepers Association (BBKA) for swarm collection advice.

Before you contact an association or an individual beekeeper, check that the bees you see are actually honeybees. You may be seeing bumblebees. For example, tree bumblebees nest in bird boxes. There will be lots of fluffy bees flying in and out of a box. Or, you may be seeing a host of solitary Mason bees nesting in the walls of an old building.

Although there may be lots of bees these aren't swarms as I've described here. These nesting bees will be gone in a few months. I'd say to leave them alone if you can. Follow this BBKA link for help with bee identification.


Just like us, honeybees want to survive and thrive. Swarming is their solution to this challenge. That's one of the things I love about beekeeping - it's a window into a world that's so different to ours. It blows my mind!

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Honeybee Democracy (2010) T.D. Seeley, Princeton


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