Why do bees swarm and what do worms do?

A swarm of honey bees
A swarm of honey bees

Before I get all technical on the beekeeping front I must share with you that I have just started a dog poo (or poop as our North American friends would say) wormery in my back yard – I’m a backyard wormer! The idea is that I establish a colony of worms and then, once they are strong and healthy, throw in the poo from my two beagles for the worms to devour and turn into compost. I think my dogs must posses extraordinary poo generating parts because these worms are going to be busy. The kit came from Earth Essentials and I have high hopes of becoming an expert worm keeper as well as hopefully being a good bee keeper one day. At first sight it looks as though I just spent a lot of money on a plastic wheelie bin and a bag of worms – worms which look suspiciously like the worms I already have in my garden, not supercharged poo eating worms, but I am prepared to give this thing a fair trial.

Anyway, back to bees. I mentioned swarming in my last post, although it may have got lost due to the turkey story, but the fact is that swarming is a big deal for beekeepers. The idea is that beekeepers keep bees, that is, keep them in the boxes we call hives, rather than let them fly off in a swarm to make a home elsewhere. That is very bad form indeed, ho hum. It matters because we don’t make much honey from a colony that has swarmed, and considering the effort we put into keeping our buzzy friends healthy I feel that we deserve some reward at the end of the season. For commercial bee keepers a big swarming problem could mean a big financial loss, and it doesn’t take too many of those to put people out of business.

We know a lot about swarming, and yet we don’t really know quite enough. There have been research projects and academic papers on the subject, which means that we can read about what the scientists say, and of course there are the experiences of beekeepers themselves, sometimes passed on by word of mouth, sometimes through teaching, mentorships and books. In very simple terms the bees want to swarm because that is how the colony reproduces, and the beekeeper does not want them to swarm because he or she wants them to stay in the hive and put their considerable energy into making lots of honey. In the end, sometimes the bees have their way and sometimes their keepers do. This is how life is.

Some of the factors involved in swarming as far as I can tell are as follows:

Time of Year

Bees evolved in forests and lived in holes in trees so it makes sense that they are programmed to swarm at the time of the year when many trees come into flower. This seems to be hardwood trees like oak and horse chestnut in my area. The first proper queen cells in my hives generally come in mid to late May and normally the urge to swarm has abated somewhat by July. The fruit tree blossoms come earlier and the bees have not built up enough strength to be able to swarm then. It seems that for me mid May to mid June is prime swarm time, partly because the strength and size of the colony is matched by the abundant pollen and nectar provided by the flowering hardwood trees. I need to ensure that I inspect my colonies every week during May and June because that is when I’m going to have to deal with queen cells.

Horse Chestnut flowers
Horse Chestnut flowers

Weather Conditions

Most beekeepers that I have spoken to agree that there are certain conditions which seem to prompt the bees to make queen cells and then swarm. When the colony is big and strong they need to be working. There is a large force of older worker bees who delight in foraging for food and who do not seem to enjoy, if that’s the right word, being confined to their hives by rainy weather. The younger bees have their duties inside the hive, raising brood and house cleaning and so forth, but the older bees want to be flying all day long – they fly until they drop, literally. The worst weather appears to be something like 3 days of rain followed by one sunny day, then 3 more days of rain followed by another sunny day, and so on. Combine this with it being the preferred time of year for it (May/June) and you are going to have some serious swarming to deal with.


Some sub-species of the honey bee are more prone to swarm than others, such as Carniolans, but even for the majority of our “mongrel” bees there is a genetic component responsible for swarming (Winston 1980). There are certain traits which have been shown to be influenced by genetics, such as defensive behaviour, hygienic behaviour, foraging, grooming, and tendency to swarm. The beekeeper can influence the genetics of their bees by using queens from stock that is less likely to swarm than others. This is why, if you have a particularly swarm prone colony, you should not raise their next queen from their own queen cells, because this will simply propagate the undesirable trait.

Age of the Queen

One of the pheromones given off by the queen is Queen Mandibular Pheromone (QMP) which is dispersed throughout the colony by the grooming behaviour of the bees. It’s presence suppresses workers from starting to make queen cells. This was confirmed by several studies that showed that administration of synthetic QMP to queenless colonies suppresses the production of queen cups (Pettis et al. 1995) if the administration occurs within 24 hours from queen loss; but if synthetic QMP is applied 4 days after queen loss no effect is observed, indicating that QMP inhibits the initiation of queen-rearing but not the maintenance of established cells (Melathopolous et al. 1996).

Queen emerging from cell
Queen emerging from cell (photo: Kathy Keatley Garvey)

It turns out that the amount of QMP that a queen honey bee produces tends to fall as she ages, so that queen cells are much more likely to be started in a colony with a two year old queen than a one year old. A study in 1969 in New Zealand by I.W Forster showed that many of the methods used by beekeepers to reduce swarming did not work, and that the single best way to suppress swarm preparations was to use queens that were in their first year, particularly Spring reared queens in their first year.

Amount of Space for the Queen to lay eggs

When the colony is building up it’s numbers and the queen is laying flat out all day and all night she needs space to lay her eggs. There is only so much comb in the hive; some is used for storage of pollen and nectar, and some is occupied by the developing larvae and pupae. Beekeepers can notice changes in the hive as the season progresses. In the Spring the brood nest is expanding outwards and cells that once held honey are used by the queen for her eggs. However, a strong force of flying worker bees combined with a good nectar flow can mean that a lot of nectar is coming into the hive in the daytime. It tends to be “dumped” in the brood nest during the day and then moved higher up in the hive later on at night, ensuring that the space for laying eggs is still there, but eventually space runs out and the area of brood starts to shrink, and cells vacated by emerging young bees are used for nectar storage. Once the brood area starts shrinking and being used for nectar storage the next stage will be the production of queens cells and the issuing of a swarm, or swarms.

Size of colony

As a colony grows, hopefully into a monster which will produce over 100lbs of honey, the possibility of swarming also grows. One factor will be the dispersion of the QMP. In a small colony the QMP is dispersed across all workers so they know that they have a healthy queen present, but in a large colony those bees furthest away from the queen may not “get the message” for some time, and they may start to behave as if they do not have a healthy queen, which means taking steps to replace her i.e. make queen cells. Furthermore, it appears that as the population density grows (overcrowding) the bees are more likely to swarm.


This is not so much a cause of swarming, but the bees should not swarm if there aren’t drones flying around looking to mate with queens. The whole point of the exercise is to establish a new colony with the old queen whilst the parent colony gets a newly mated queen, and for that to happen we need there to be both queens and drones. So another sign for beekeepers to look out for is the presence of drone brood. Drones will emerge 24 days after the egg was laid and they take another 12 days or so to be sexually mature.

Right then, at some point I will write about what the beekeeper can do about all of this. There are two stages to the beekeepers job as far as swarms go; prevention and control. Swarm prevention is what we do to try to prevent swarming – the bit when mankind takes on Mother Nature and says, “back off!” It doesn’t seem to work that well but one must at least try. Swarm control is what we do when we accept that our hive has decided to make swarm preparations and ignore our attempts to persuade them to stop procreating and stay home and watch TV instead.

Clover field - Canterbury Pains
Clover field – Canterbury Pains, New Zealand (photo: Peter Bray)

I’m flying out to New Zealand this month and as there are no walruses living in the Southern Hemisphere it could be a difficult time for me. There are plenty of bees though, and for them it’s mid Summer, so I’m looking forward to it. I might even get to taste some clover honey and see what this Manuka is all about.

3 thoughts on “Why do bees swarm and what do worms do?

  1. […] referred in my last post to a study in New Zealand by I.W. Forster which […]

  2. We’ve just ordered a Dog Poo Wormery, just wondering how yours is getting on?

    • Hi, the dog poo wormery seems to be doing its thing. I never actually see the worms unless I dig around in there, which is not especially pleasant, but the poo is being turned into something else…

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