bees swarming on tree branch

Why Do Bees Swarm? Breaking Point And Beyond

Last updated on February 3rd, 2023 at 11:40 am

A giant ball of bees can be quite an intimidating sight for the inexperienced.

But what creates this fascinating migration at such a large scale?

Let’s take a deep dive into why bees swarm including everything you need to know about honey bee swarms, one of nature’s most fascinating reproductive processes.

The short answer to why bees swarm?

When a honeybee hive population reaches breaking point it will begin to swarm. The reigning queen and anywhere from a third to a half of the current colony will leave to find a suitable location to build a new nest.

The remaining residents will set about producing a new queen that will quickly take her place as the new matriarch.

Do all bees swarm? 

No, in fact, it’s only the honey bee (apis mellifera) that swarms to find a suitable home. 

Bumblebees, carpenter bees and mining bees live in much smaller concentrations and have very different ways of finding a new place to live and raise young.

What causes bees to swarm?

In most cases, it’s overpopulation that initiates a swarm of bees but there are some other more sinister reasons honey bee colonies may choose to vacate their nest.


An ample old tree hollow can quickly become too small for an ever-growing colony of honeybees.

In most cases, a hive will swarm because there are too many honeybees for the size of the hive. This is common with managed bees as the frames become packed with honey and larvae.

If left unchecked this could pose serious risks to the existing nest with a higher likelihood of infection and disease due to the cramped conditions.

Other factors

Sometimes hives will fall prey to disease, parasites or a lack of food and water which can lead to a forced exodus.

The use of pesticides in the local area can also cause hive swarms in an effort to escape the pesticide’s poisonous effects on living organisms. 

In these cases, the worker bees and the queen will make no preparations for a successor or the continued existence of the current hive.

All the bees capable of taking flight will abscond in one large swarm in hopes of finding a suitable location for a new hive.


Honeybees vary considerably in their temperaments and in their swarming habits.

However, all honeybee colonies act on a level higher than the individual bee. This ‘hive mind’ of sorts will be motivated to reproduce and continue the survival of the species.

One of their strategies to increase the species population is to send out an expeditionary force to try and start a new colony elsewhere.

This means that some of the occupants of the hive will begin to swarm despite ample space left remaining in the nest.

This will then allow two queens in separate hives to both continue to produce a brood. Effectively doubling the rate of reproduction.

What happens when bees swarm? 

When overpopulation induces a swarming event to find a new home the flight is not instant. Careful prior planning and strict execution are required to transplant half a hives population.

Normally occurring in spring during warm weather, the bees will begin by putting the queen on a diet.

Due to their size, queen bees are not the best flyers and require rests along the way, any excess weight that can be shed before the flight will make the swarm’s journey safer and shorter.

Unlike the much heavier queen bee, the bees who are departing with her will gorge on honey.

Using glands in their abdomen honeybees can produce wax which oozes from their pores and forms flakes.

Worker bees will then chew these flakes to create a putty that can be used to make honeycomb structures with.

This will be an essential building block when establishing their new hive. 

*Interesting fact – Most queens are required to fly over 250m to find a new location for the hive.

Within the hive, workers will regularly construct new queen cells to harbour royal larvae ready to supersede the old queen after she leaves.

Under normal circumstances, queens will not lay eggs in the queen cups and will continue to produce drone and worker bees.

But when the swarm event is imminent she will lay eggs that will be fed a diet of exclusively ‘Royal Jelly’, a much more nutrient-dense food than that fed to normal new brood.

When the first queen hatches she will set about ensuring she is the only surviving successor by killing any developing rivals.

This process is aided by the young workers who will remove the wax capping to allow the queen to secure her reign.

The heart of the swarm

Once all preparation is complete the honeybee queen will leave somewhere between a third and half the hive, taking to the skies in search of a new home.

The half of the colony that leaves the old nest is called the ‘Prime Swarm’.

At first, the swarm will complete a small journey. In some cases, this may just be a trip to a neighbouring tree branch well within sight of the existing hive or nest.

Locating the new nest

From this position, scout bees will be deployed to search out potential sites for the new hive. The location will need to be sheltered from the elements but will still require some sunlight for warmth.

It will require a small protected entrance and no other unwanted inhabitants within.

When all of these criteria are met or at least partially met the scout bee will return to the swarm to report her findings. 

These can include:

  1. Tree hollows
  2. Man-made cavities in buildings
  3. Caves
  4. Bee hives
  5. Chimneys

After finding what they believe is a suitable new nest site they return to the swarm to report their findings.

Upon the scout’s return they are judged on the level of energy in their dancing to determine which scout’s location will be an appropriate site for their new home, this charming communication method is called a ‘waggle dance’.

The vigour and energy portrayed in this majestic dance of the honeybees will communicate the new nest site’s potential success, direction and distance.

If this dance is performed with particular vigour and energy other scouts will be persuaded to inspect the location. 

This time frame for this process is approximately three days with one location displaying itself as a new winner. Once a potential nest site gets approximately 80% of the scout bees’ approval the decision is made.

Once this startlingly democratic process has been completed the whole swarm will take flight with scout bees flying above the swarm to guide it safely to the new location. 

Human interaction with swarms

Considering the population of both ourselves and the honeybee, instances of human and swarm interaction are relatively low but seem to be on the rise in recent years.

This could be due to a considerable increase in urban beekeeping or the exceptionally high temperatures we have been experiencing in late spring and early summer.

On the whole, honeybees are generally fairly calm during their swarming period. Despite its somewhat threatening look a whirl of bees is gorged on honey and remains in a fairly docile state.

The swarm will only attack in defence if they feel intimidated or if the queen is threatened (like when you see morons dousing them with a hose pipe).

If you come across a swarm in an urban environment where they are a threat to themselves or other people your best course of action is to contact a local beekeeper in the hope they have a vacant hive that they can be transported to.

You can use the British Bee Keeping Associations’ handy little tool to locate a swarm collector close by.