Why do bees swarm and how can it be prevented?

Every year, during the spring while driving, I run into four or five bee swarms with my car. They seem to be everywhere flying in all different directions yet maintaining a somewhat disorganized grouping.

I would wonder “Why did that beekeeper allow his bees to swarm and how could he have prevented it?” So I drilled down a little on the subject and this is what I discovered.

Swarm Photoshopped CJBD Street Tree in Oakland Small

Why do bees swarm and how can it be prevented?

Bees swarm because:

  • The hive becomes very overcrowded.
  • The Queen’s pheromone is diluted by the mass of the bee population.

Bees don’t swarm when provided additional space by adding:

  • Adding a honey super to the beehive.
  • Or adding a brood box using the “checkerboard” technique.

What do bees need to be able to swarm?

  • They need a new viable Queen in the old hive.
  • They need lots of bees that will follow the old Queen as she leave the hive in a swarm.

Overcrowded Conditions:

In overcrowded conditions, worker bees start to build Queen cells, an early warning sign of bees starting the swarming cycle.

Worker bees start to build out Queen cells to raise a new Queen in anticipation that half of the hive will be leaving in a swarm. They will need a fertilized Queen to get busy laying eggs just to replace the workforce they have lost to the old Queen’s swarm.

It is always the old Queen that leaves the hive in search of a new home to build a new hive. About half of the beehives population will follow the old Queen in a swarm as they seek a new home hive.

Until the reigning Queen decides to leave the hive with a swarm, she will sting to death any new Queen that is born or destroy the swarm cell before the new Queen can emerge.

Unlike the worker bees, the Queen can sting as many times as is needed while a worker bee stings once and dies.

Queen bees do not sting human beings for some reason, some say stinging a human is beneath them.

Beekeepers do not want their bees to swarm. If they swarm, the beekeeper loses half of the hive production capability to some natural habitat such as a hollowed out tree, and a lot of honey that the hive has already produced and stored. The swarm will take as much honey as they can carry when they swarm.

That is not in the beekeeper’s interest at all, so the smart beekeeper keeps a close eye on his beehive in the early spring for any signs that the hive is preparing to split and swarm.

Bees can multiply very quickly. In the winter time they can reduce their numbers down to about the size of a baseball to ride out the winter. Upon the arrival of spring the Queen gets busy laying eggs. She can lay up to about 2,500 eggs a day, so it doesn’t take very long to be in an overcrowded situation.

What are the early beehive warning signs of swarming activity?

  • Worker bees constructing drone birthing cells is the first very early sign.
  • The Queen bee beginning to slim down is a very early sign as well.
  • Worker bees constructing Queen cells is the third early sign. For many beekeepers, this will be the first sign recognized.

During swarming season, spring, the beekeeper needs to inspect the hive all the way down to the bottom board at least every two weeks.

One of the very early signs of swarming is drone brood being cultivated. When drone brood is being cultivated, the swarming event is generally going to take place within the next two to three weeks. The bees are increasing the drone population in preparation for mating.

Very early detection of drone cell building can be done by placing an empty frame in the middle of the hive at the beginning of swarming season and frequently check that newly inserted empty frame to see if the bees are building worker bee birthing cells or drone birthing cells.

Learn more about reading a brood frame….

Drone cells are a red flag for swarming while worker bee birth cell construction is a sign the hive is strengthening its work force in anticipation of building the hive stronger.

Drone birth cells are larger than worker bee birth cells by about 30% making them easy to identify to the trained eye.

The worker bee birth cell and the honey storage cell are much closer in size making it much less identifiable by cell size. Cell caps are a better way to differentiate worker bee brood and honey cells, but we are looking for the EARLY signs of drone cell construction to tell us what the bees intentions are.

If they are building larger cells, usually constructed in the bottom two corners of the frame, they are constructing drone birthing cells, one of the earliest signs of a potential swarm.

Drone brood is usually grouped together in one or both corners of a brood frame. Capped drone cells are dome shaped construction as opposed to the relatively flat surface of a worker bee birth cell.

Drone cell construction will precede the construction of Queen cell construction, so it is a very early sign of a potential swarm of the hive.

A Queen bee will slim down as the hive prepares to swarm, this is also an early sign to be aware of to prevent swarming.

How can beekeepers prevent their bees from swarming?

  • Inspect the hive’s brood frames regularly in the spring looking for drone and Queen cell building.
  • Scrape the Queen cells off the frame.
  • Provide additional space by adding a honey super or a third brood box using the “checkerboarding” technique.

Queen cells will always “hang down”, they are most frequently found hanging from the bottom of a brood frame.

Worker bees start to construct Queen cells in overcrowded hives in anticipation of a swarm happening, they don’t want to be left Queenless, the hive would die.

Queen cells will almost always be on a “brood” frame, a frame that the bees use to raise new bees. Normally, there are less than half of the frames that have brood in them. These are the frames the bees will likely choose to build Queen cells in preparation of swarming.

Once Queen cell construction and verification of egg or larva are in the cell, the swarming could take place within the week. Or the old Queen will simply kill off the new Queens as they hatch (or destroy the Queen cell before the new Queen hatches), until she decides to leave the hive in a swarm. It is entirely her choice.

That is why worker bees construct Queen cells daily. A new Queen hatching every day will assure there will alway be a successor to the old Queen.

Any new Queens, born after the first surviving new Queen, are either stung to death by the newly reigning Queen or she destroys any remaining unhatched Queen cells, otherwise known as “swarm cells”.

A Queen cell containing an egg or larva is referred to by beekeepers as a “swarm cell”.

Sometimes bees make “potential” Queen cells, called Queen cups, but there won’t be any egg or larva in these cells. Bees tend to make some of these empty Queen cups “just in case”.

Queen cups are not a sign the bees are about to swarm, but Queen cells (those with egg or larva inside the Queen cell, swarm cell) is a good indicator of a potential swarm.

If a beekeeper finds swarm cells in the hive he will destroy the swarm cells before adding a super or third brood box, thus greatly decreasing the potential for the hive to swarm. However, be very careful with this technique. The beekeeper must see the Queen, or at least evidence of the Queen laying eggs recently. If the Queen is not seen and no evidence of recent egg laying is seen, it is possibly the hive has already swarmed.

When the Queen first lays an egg in a cell it will be seen as a small white dot at the bottom of the cell.

If there is a “glob” of jelly-like substance in the cell it tells the beekeeper that this egg has been laid in the recent past but is not a “freshly” laid egg. The white jelly-like substance is Royal Jelly.

Once the egg is hatched to the larva stage the worker bees will cap the birthing cell with wax to complete the metamorphosis from larva to a live bee.

A beekeeper can determine the stage of larva development by looking at the color of the wax cap placed over the bee’s birthing cell. When the bee’s birthing cell is initially sealed by the worker bees, the sealing cap will be light yellow.

Freshly laid eggs will be covered in a light yellow, indicating recent activity by the Queen bee. The wax covering will darken as the larva continues to mature. Some claim this darkening process is caused by larva excrement within the cell as the larvae develop over time.

But remember, it is always better to see the Queen instead of just recent activity signs, she still could have already left the hive.

If all the swarm cells are destroyed, and the hive has already swarmed, the hive will be left with no Queen and no way of producing a Queen. It will be the death of the hive.

When a beekeeper finds swarm cells there are two options available to the beekeeper:

  • Option 1: Destroy the swarm cells.
  • Option 2: Remove the Queen cell intact and place them in a nuc along with some of the hive’s bee. The hive will not miss the transferred hive bees as the hive is already overpopulated.

This is a great way to start an additional hive or sell the nuc for additional profit.

Adding A Super To The Hive To Prevent Swarming:

The most common way to provide additional space for the overcrowded beehive is by adding a super to the hive. This is just adding a third story to the beehive that is filled with frames for the honey bees to fill with honey.

Adding a super to the hive is considered the most effective way to prevent swarming.

Most beekeepers will add frames to the super that already have comb built out or a frame with “foundation”, a structure to help the bees get started building cells into which they can make honey.

The less work the bees have to do building wax foundations, the more time they will have gathering nectar to make honey.

Most beekeepers will put a Queen excluder between the brood boxes and the newly added super, however there is a strong contingent of beekeepers that do not use Queen excluders at all, but that is another topic, deserving its own dedicated article.

Most supers are added to the beehive with the intent to harvest honey from the supers at harvest time, therefore the beekeeper would have normally added a “Queen excluder” to prevent the Queen from entering the super and depositing eggs in the honeycomb (this would be called “brood”) and most beekeepers do not want brood in their honey harvest.
They want just pure unadulterated honey.

If the hive becomes overcrowded before the beekeeper adds a super, one will often see a phenomia know as “bearding” on the front of the hive.

Bearding happens when there are so many bees they can’t all fit inside the hive, so they attach themselves to the front of the hive forming a mass of bees hanging on the front of the hive, looking much like a beard on the hive, hence its name, bearding.

Some seasoned beekeepers say that if bearding happens it is too late to add a super to prevent the inevitable swarming. The beekeeper’s best option at this point is to try and capture the inevitable swarm in a “bait box” as the bees leave the hive.

If the beekeeper is successful at capturing their swarming bees they have double the number of hives they now own instead of losing 50% of their productive bees and still only having one hive.

Beekeepers would prefer to add a super and prevent the swarm instead of splitting the bees into two hives.

Adding a super makes for a stronger and more productive hive than the combined efforts of two weaker hives.

So when the brood box is full of bees on every frame, even if there is no Queen cell construction yet, experienced beekeepers suggest adding two supers to the hive to give the bees more room to work.

Some beekeepers will add a super without adding a Queen excluder. If the Queen is not blocked from entering the super, either with a Queen excluder or a domed honey filled cap on every frame, she will enter the super and start laying eggs in the honeycomb.

Adding a third brood box using the “checkerboard” technique to prevent swarming:

Some beekeepers try to produce a highly productive hive by allowing the first added super to be used as an additional brood box. The theory is, the greater the workforce the faster honey will be produced. Beekeepers will later add additional supers, using a Queen excluder, and expect a quick build up of pure honey in the new super(s) which they intend to harvest at the right time.

When adding a third box to be used as another brood box, many beekeepers will be aware that the Queen bee will not cross honey filled cells in search of new cells to lay more eggs, therefore they use a technique known as “checkerboarding” to assure the Queen can access the newly placed third brood box.

As the bees successfully “over-winter”, they eat all of their honey stores starting in the bottom brood box of the hive and work their way up through the honey stores into the second story of the hive.

In January bees will be mostly in the second story of the hive, having eaten all the honey stored in the bottom box of the hive.

In February the Queen will begin laying eggs in the empty cells that contained the honey the bees consumed to survive the winter. She begins to lay a lot of eggs.

In March the two bottom brood boxes combs are almost completely filled with various stages of developing bee larva. A LOT of new bees are being reared.

When all these new bees are hatching (the new workforce to collect nectar and pollen from the approaching spring nectar flow) the hive becomes overcrowded and overcrowding is the reason bees swarm.

One way to prevent this natural progression to swarming is to give the bees more space in the bottom two brood boxes by adding a third brood box. The correct time to do this addition is in March when the frames in the brood boxes are becoming crowded.

The new brood box needs to be the same size as the overcrowded brood boxes below it because the beekeeper will be pulling frames from the two bottom brood boxes and inserting them into the new third story brood box.

Typically the second story brood box has a honey cap on the top of each frame. This means there are honey filled cells all across the top third of the second story brood box frames and distributed in a “dome” shape at the top of each frame. This is the leftover honey stores that were not consumed during the winter.

The Queen will not cross these honey domes in search of new opportunity to lay more eggs.

The beekeeper takes a couple frames of brood out of the bottom box and a couple frames brood out of the second story box and disperse them into the third story brood box. The beekeeper then fills the remaining space in the third story with empty frames for the bees to fill out.

Replace the removed frames in the first and second story with empty frames.
Bees do not like to have open frames next to frames of brood, so they will quickly fill in these blank frames with more brood cells.

Using this third brood box technique accomplishes two things that will prevent swarming:

  • Adding these empty frames allows the Queen a path to find the newly added third brood box. Without this pathway she will continue to lay eggs only in the first and second story brood boxes and when she has no ability to find empty cells to deposit eggs, she will leave the hive in a swarm.
  • It adds significant additional space to the hive and decreases the over-crowdedness thereby greatly reducing the primary cause of honey bees swarming, overcrowding.

Adding this third brood box will build a massive workforce for the hive and will increase the amount of honey this hive produces.

Using the checkerboard approach, once the third story box is filling out with the honey dome pattern, it is time to put the bees to work producing pure unadulterated honey by adding a super as the fourth story of the hive.

Once the super frames are filling out with honey, the hive is ready to accept another super.

There are two techniques that make the bees work harder once this second super is added to the hive.

  • Take some of the honey frames from the first super and place them in the second super with blank frames between the transplanted honey frames. This will cause the bees to feel compelled to fill the empty frames, they do not like empty frames next to filled honey frames.
  • Another option is to add the second super to the top of the brood chamber and place the first super on top of the second super giving the hive an empty super between the brood boxes and the filled first super.

As a general rule, bees will never need more than three brood boxes.
Usually, at about two and a half brood boxes filled out, the nectar flow is over and the Queen bee’s egg-laying will diminish, the size of the hive will diminish, and the need for new brood box space will diminish. Some say if there are brood boxes already in place, there really is no need to inspect for swarming.

What do I do if my bees want to swarm in the fall?

  • Capture the Queen in a Queen cage.
  • Place the captured Queen in a nuc for safe keeping.
  • Allow the hive to hatch the new Queen they are rearing.
  • Kill off the newly hatched Queen.
  • After all the Queen cells are hatched and killed off, put the original Queen back in the hive.

Overcrowding is the reason for bees to swarm regardless of what time of the year the overcrowding happens. Be sure to keep your eyes open for overcrowding and Queen cell construction in the fall after the fall nectar flow.

A swarm of the hive in the fall will leave the hive with a Queen that has not mated so she will not have the ability to lay eggs and insure the survivability of the hive.

And the old Queen that has swarmed, with about half the hive, does not have the capability of carry enough honey with them to survive the winter.

A swarm in the fall is a lose lose situation.

Final Thoughts:

  • Sometimes a hive that is preparing to swarm will abandon the swarming activity when there is an abundant nectar flow. Nectar flows are a biannual event when flowers produce a lot of nectar. These nectar flows are in the spring and late summer, each lasting a few weeks.
  • Some beekeepers try to prevent swarming by clipping the Queen bee’s wings but this technique is usually just marginally successful.
  • Remember, when you lose half your bees you also lose some of your honey. The swarming bees will take as much honey with them that they can carry.
  • Dearths are the several week period of time that flowers do not produce much nectar. They occur after the two nectar flow events, one nectar flow is in the spring and one in the fall, each lasting several weeks.
  • Foraging bees begin their work of bringing in nectar and filling the frames with honey as soon as the spring nectar flow begins. As they fill the frames with honey, the Queen runs out of cells in which to lay more eggs. This starts the process of preparation to swarm.
  • The bees will recognize the approaching nectar flow with the first warm days of the new year. This happens much sooner than one would expect; they must be strong in numbers before the spring nectar flow starts.
  • The Natural Instinct of bees is to propagate for survival, so in the very early spring the Queen gets busy laying lots of eggs. When the Queen lays enough eggs to overcrowd the hive the bees will swarm.
  • Some beekeepers will not use Queen excluders because all worker bees are not the same size and passing thru the queen excluder can shorten a worker bees life by up to 50% because of the wear-and-tear on the worker bee’ wings as they pass through the queen excluder to deposit their foraged nectar and pollen in the frames of the honey supers. Learn more about Queen excluder vs no Queen excluder…..
  • Using the checkerboard technique, you can elect to use the brood frames that are removed from hive to make a nuc or split the hive, but a super will still be added to the donor hive to relieve the overcrowded factor which is the causes swarming in the first place.
  • Bees regulate the temperature and humidity in the hive very precisely. The temperature they maintain the hive is 95 to 98 degrees Fahrenheit. When a hive is opened with the outside temperature at 70 degrees Fahrenheit it is like opening the front door of your house on a winter’s day. They get a very cold blast of air that completely disrupts the hive’s internal environment. The experts recommend getting into and out of the hive in about five minutes, more quickly if possible. Learn more about hive temperature and humidity…..
  • The best time of day to open and inspect the hive is mid-day when a lot of the hive’s bees are out in the field foraging.

Related topics:

What type bait box should I use to catch a swarm of bees?

There are many types of bee bait boxes. All types of bait boxes work well. More importantly is the size of the bait box. Small bait boxes catch small swarms. Big bait boxes catch big swarms. And afterall, bees swarm because they need more space.

How can I find a honey bee hive in the wild and capture it?

  • Capture a few bees to a hand held bee capture box.
  • Mark the bees with color dots.
  • Feed the captured bees a great food source.
  • Release the marked bees and note their flight direction back to their hive.
  • Time their return to your great food source.

Happy BeeKeeping

(with “keeping” being the operative word here)

Paying It Forward

Robert Donaldson

I am Elizabeth's father, a physical therapist, and someone who has completely landscaped our family home's nearly 1/2 acre lot after losing our home and landscape to the Thomas wildfire in 2017. All landscaping was done to accommodate our wildlife friends, especially the birds and bees.

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