The memory of swarms

I’m writing this waiting for the drizzle to clear so I can go to the apiary and make up some nucs for swarm control. Without implementing some form of swarm control it’s inevitable that my large colonies will swarm 1.

Swarming is an inherently risky process for a colony. Over 75% of natural swarms perish, often because they do not build up strongly enough to overwinter successfully.

As a mechanism for reproduction swarming is somewhat unusual in that the intact colony is split into two not fully functional ‘halves’ 2.

By not fully functional I mean that neither the swarmed colony, nor the swarm are guaranteed to survive.

The swarmed colony lacks a queen, but has ample stores.

The swarm has a queen but has only the stores carried in the bellies of the workers.

The swarmed colony needs to rear a new queen. The swarm needs to find a new nest site, move there, build comb, rear brood, forage etc.

That seems like the very opposite of intelligent design, but it’s the way evolution has made things work. This being the case it involves a whole range of compromises and quick fixes that make it work.

One of these involves the memory of worker bees, which is what this post is about.

Two-stage swarming

A range of events within the hive – which for reasons that will become obvious I will term the original nest site – trigger the urge to swarm. I discussed some of these when covering swarm prevention. Swarming is then essentially a two-stage process. 

The two stage process of swarming

The first stage is the swarm leaving the original nest site and establishing a bivouac nearby. This is the classic cluster of bees hanging from a branch.

The bivouac sends out scout bees to search the nearby area for potential new nest sites. After ‘discussion’ (comprehensively covered by Thomas Seeley in Honeybee Democracy) between the scouts they reach a consensus of the best site.

The second stage is the relocation of the bivouacked colony to the new nest site. For example, this could be the church tower, a hollow tree or a bait hive. This site is likely to be within a few hundred metres of the original nest site, but can be further away.

All of which should raise some questions in the minds of beekeepers who are familiar with the “less than 3 feet or more than 3 miles” rule.

Have these bees not read the rules?

If you want to move a hived colony of bees you’ll often be told, or have read, that you need to move them either less than three feet or more than 3 miles.

Worker bees have a foraging range of about 3 miles. Within this range they have an uncanny ability to return to the hive location using features of the landscape to orientate themselves. The ‘final approach’ uses scent from the hive entrance.

Therefore, if you move a colony 3 feet they’ll still find the general location using landscape features, and then orientate to the hive entrance using scent.

If you move a colony 10 miles away everything is new to them and they’ll embark on some orientation flights to learn the new landscape features.

But if you move the colony a mile they’ll use the landscape features to return to the site of the original hive … to find it gone 🙁 3

Swarms break all these rules.

The bivouac is (in my experience) always more than 3 feet from the hive entrance. If the scout bees make the choice (e.g. selecting a bait hive to occupy), the swarm always relocates to a new nest site less than three miles from the site it left 4.

And a beekeeper who drops a bivouacked colony into a skep can move it wherever she wants, even back to the same hive stand it recently vacated.

If the swarm followed the rules, the majority of the workers would return from the bivouacked swarm to the original nest site.

At least they would if they had orientated to the original nest site in the first instance.

Are the bees naive?

About half of a workers life is spent as a forager collecting water, pollen or nectar. But before they venture out of the hive, the first half of a worker bees life is spent building comb, nursing larvae or cleaning cells.

Therefore, one possibility is that the bees present in a swarm have no knowledge of the hive location because they’ve never before left the hive.

We know that the proportion of workers that leave the colony when it swarms is about 75%. This has been determined in a number of independent studies and is remarkably consistent, irrespective of the size of the colony that swarms.

If 75% of the workers leave the colony when it swarms it is mathematically impossible for the swarm not to include older foragers (assuming the laying rate of the queen is steady).

In fact, we don’t need to resort to any underhand mathematics as the age classes of bees in a swarm have been measured. I’ve discussed this before when comparing natural and artificial swarms.

Age distribution of bees in swarms

Age distribution of bees in swarms

The median age of adult bees in the hive is 19 days. The median age of bees in a swarm is 10 days. Therefore swarms do contain younger bees, but not exclusively so.

One of the reasons for this bias towards younger bees must be to do with the relatively short lifespan of foragers. Many of the older bees in the swarm will have perished long before the new brood laid by the queen emerges.

Permanent amnesia?

The bivouacked swarm doesn’t dwindle in size as the older foragers drift back to the original nest site. Other than a few hundred scout bees, the majority of the bivouacked swarm huddle together to protect the queen, buried somewhere in the centre, from the elements.

They don’t fly or forage … they’re waiting for the signal from the scout bees that a new nest site has been located.

And, once they relocate to the church tower, the hollow tree or a bait hive, the older foragers stay in the new nest location. It’s as though the bees in a swarm that previously knew where the original nest site was have amnesia.

And this makes sense. If they did return to the original nest site the swarm (whether bivouacked or relocated) would shrink in size and it’s chances of surviving would be severely diminished. Other than a full belly of honey a swarm can rely on nothing. They need as many bees as possible to take on all the roles needed to establish a new colony – comb builders, nurses, foragers etc.

But have they really forgotten the original nest site?

Temporary amnesia?

It turns out that swarms do retain a memory of their original nest site.

In 1993 Gene Robinson and colleagues demonstrated that a swarm shaken out from its new nest site preferentially returns to the original nest site, rather than to an equidistant alternate 5.

This ability must rely on the memory of the foragers in the swarm. Therefore it is likely to be lost in a relatively short time (days, not weeks) 6.

Firstly, the foragers will be busy reorienting to the new nest site, effectively overwriting the memory of the original nest location. In good weather this takes just a couple of days.

Secondly, these ageing bees don’t have long to live, so there will be ever-decreasing numbers of them to lead a shaken out swarm back to the original location.

Rain stops play

Sometimes the bivouacked colony never relocates to a new nest site. Either the scouts never achieve a consensus or – more likely – bad weather forces the swarm to hunker down.

When you hive a bivouacked swarm you will often find a small crescent or two of new wax on the branch they were clinging to. If the bees get trapped by bad weather I think the comb building continues. It’s not unusual to find comb in hedgerows near apiaries where bees that have got trapped have ended up trying to make a new nest.

Natural comb

Natural comb …

What does the memory – or lack of it – of swarms mean for practical beekeeping?

The (temporary) amnesia of swarms means you can collect a bivouacked swarm and move it wherever you want. A swarm that relocates to your bait hive can also be moved, but don’t wait too long. Within just a few days of a swarm arriving the bees will have reoriented to their new location. I always try and move bait hives to their final location within three days of a swarm appearing.


The drizzle stopped and I spent the entire day finding queens and making up nucs.

Note to self … a super-strong colony with no queen cells, wall-to-wall brood and no very young larvae or eggs probably has a faulty queen excluder 🙁

Second note to self … Sod’s law dictates that the colony with the faulty queen excluder probably has supers filled with drone comb 🙁


  1. The queens are all clipped, but that’s not so much swarm control as damage limitation.
  2. And, as we’ll see in a minute, it’s not divided equally either.
  3. There are all sorts of tricks to circumvent this rule, but that’s not what this post is about. I’ve written about some of the tricks that can be used to move colonies intermediate distances previously.
  4. More usually 200-800 metres away.
  5. Robinson G E and F C Dyer (1993) Plasticity of spatial memory in honey bees: reorientation following colony fission. Animal Behaviour 46 : 311-320.
  6. This is reasoned speculation – I don’t think anyone has measured this experimentally.

21 thoughts on “The memory of swarms

  1. Jeremy Quinlan

    My recollection is that Tom Seeley emphasised that the bees’ decision where to go was by quorum not consensus.

    1. David Post author

      I think you’re right Jeremy … my mistake. I’ll check when I’m next near my copy of the book. It’s a slightly subtle distinction and perhaps not too important in the context of what’s written here, but useful to be correct. When I get hold of my copy of Honeybee Democracy I’ll add a footnote …

      With thanks

  2. vince poulin

    Such relevance. I’m sitting here after having one of our hives swarm yesterday. It started by a volcano of bees being wind swept across the garden. Within minutes on to an overhanging tree forming – your language – a bivouack. To high for me to reach. Soon a twig breaks and down comes 1/3rd+ bees on top an adjacent carport. Scramble for equipment – box, dust pan, and brush. All bees successfully scooped or walked into the box. Gentle as kittens (you say 75% nurse bees – I believe it). Sprayed with sugar solution and dumped into a bait hive for over-night. 5 am this morning I transferred them to one of the new 2020 NUCs. Using newspaper to join. All happened within our back garden all in less than 60 feet. The remaining cluster is still in the tree. I placed the near empty bait hive used for the transfer just below the remaining bivouacked bees. Also scrambled together a second bait trap and placed it about 15-18′ away (at property boundary). Residual bees left in the transfer box have been flying in and out all day but not enough action to entice the bivouack to break ranks and come down. Now – the second trap has had visitors. The odd bees – possibly scouts – assessing digs. Tomorrow will be telling. Will the bivouack be off to the Church Tower or the bait hive? David, I worked hard at swarm prevention. Read all your posts! but hives here have exploded – insane nice weather. We over-wintered 1-strong 2019 package and 3-2019 NUCs made from that package. I removed frames – obviously not enough but enough to set-up 4 new 2020 NUC’s. 2-now have mated queens (from grafting) and 2 virgin queens from swarm cells. I added supers and removed all capped honey frames as soon as I could to increase space (4 kg of honey). Despite all of this I got queen cells in 2-hives. All of your posts were playing out before my eyes. I took further action – but not drastic enough. I removed all swarm cells. A bunch went into NUCs having failed grafted cells. Those hatched giving us 2-new virgin queens. Such a fine line, but hey – it’s OK – two honey supers need only a few days to harvest (likely 8 more kg). Also two under positioned mixed-honey brood boxes (50% nearly capped honey). Could be 15 kg. An amazing spring. All this and we are yet to be in the primary flow season. It is why the hives populated so furiously. It’s OK – I don’t mind a bunch mountaineering – bivouacks are great especially at 14,000′.

    1. David Post author

      Hello Vince

      The beekeeping season often seems to take ages to get started properly and then – wham! – suddenly there’s too much to do and bees everywhere. Some things go well, some things go badly. I remember years ago in which all my hives (5 or 6 perhaps) simultaneously had no queen, either because they’d swarmed or because of my cackhandedness. I’m usually a bit more in control of things now … and if there are queen cells I pretty much always take action. Knocking them back can hold the colony back a few days, but it’s risky and if you miss one … adios.

      I try not to give my bees a choice of bait hives too close together. I’m not sure if this really matters, but I want them to have one choice at a particular site. All of my bait hives are essentially identical and I get concerned about splitting the scouts up too much.

      I hope the main flow goes as well as the start of the season. Here it’s a bit too cool, but there’s still a fortnight or so to go before the spring crops go over and it’s predicted to warm up next week. All of my colonies have some pre-emptive swarm control (due to my location and lockdown) so we’ll see how they behave over the next month while requeening.


      1. vince poulin

        David – Question? Checking the hive that I think swarmed it remains filled with bees along with 3-nicely formed capped queen cells. The inspection was incomplete due to rain – one brood box (lowest) was not checked I saw lots of bees. I can not tell from the number of bees the hive swarmed. I’m not entirely certain this was the hive but the queen cells suggest it is. I did not find the queen in Boxes 2 and 3. The hive is an overwintered NUC from 2019. In an inspection 2-weeks ago I found a similar number of capped queen cells but the hive queen-right. I removed all I found along with about 4-frames of bees and placed them in new NUCs – 2-hatched. My inspection 1-week ago found no evidence of queen cells nor did I see the queen. What initiated the swarm? Population growth? This hive expanded rapidly this spring. So much so the hive became filled with honey. Most brood frames had many cells filled. To give space I removed frames and supered. That super over the past two weeks has been filled and 95% capped. Brood Box 3 is mostly capped and uncapped honey (80%). I see two choices going forward: 1. Remover all except one capped queen cell and let the hive re-queen naturally, or 2. Remover all capped queen cells and re-introduce a mated queen to the colony. I have two recently mated queens and 2 virgin queens. If I re-queened I could take the capped cells out along with their frames of bees and place them in the NUC and start one new NUC. What do you think? Which has the least risk of casting new swarms and leaving with a newly mated queen?

        1. David Post author

          Hi Vince

          Diagnosis by internet is almost impossible … your idea of lots of bees might be very different from mine.

          Colonies usually swarm (weather permitting) around the day the new cells are capped. Unless the queen is clipped in which case they’re delayed a few days, perhaps until the new queen(s) emerge. It seems odd that there were QC’s a fortnight ago (and the colony was Q+) but none a week ago. What’s more important than seeing the queen is seeing if there are eggs present. If not they’ve likely swarmed if there are sealed cells present. A strong colony can swarm and still seem full of bees.

          If the recently mated Q’s are good quality I’d be tempted to use one of them. Faster than letting the colony requeen, so you might be able to exploit the nectar flow. Remember that a colony is unlikely to accept a new queen if there are cells present. Knock them all down (unless you make a nuc up as suggested, in which case save one for that), wait three days, check again and then put her in a cage into the colony. If they attack the cage don’t let her out. Alternatively you can make up a nuc, again with no QC’s, introduce the Q to that and then unite it back to the original colony. Nucs are always easier to requeen.

          I’ve been meaning to write about queen introduction for a couple of years but never really feel qualified. About 95% of mine ‘just work’ and I’ve never found it a problem. I certainly don’t have enough experience to give an account of a wide range of different methods.

          Good luck

          1. vince poulin

            Thanks greatly David for the direction. How about this? I take my best 2020 NUC – build this spring (good looking queen) and combine that NUC with the swarm hive using newspaper. Before doing this I’ll remove all queen cells, wait the 3-days to ensure I’ve got all those cells and then combine with the NUC. Yesterday I completed full inspection on the hive. Queen cells everywhere. No eggs, no queen. Removed one frame of bees containing two queen cells plus two frames of bees and moved to a NUC. I’ll do this again to create a second NUC and to provide space given the NUC I will be adding is strong. It is contrary to your experience about me finding capped QC’s and still having the queen present. But – as you expected the hive did swarm. I did not stop the clock by simply removing the first batch of QC’s. I though it might work because I defied the odds on another of my hives. Also a very strong hive. I discovered capped QC’s just after reading your swarm prevention post! I really did not want to split the hive because it was my best. I defied the odds by destroying the QC’s and reducing the hive by removing frames of bees. I pulled 3.5 kg of honey off the hive – improving space. It seems to have worked. They did not swarm and the super is nearly re-filled. This is why I tried doing the same to the swarm hive but in this case it failed. I’ll make preparation for the NUC transfer. I do like that idea – if successful it re-queens and replaces the frames of bees removed for NUC building.

          2. David Post author

            Hi Vince

            Keep good notes! You never know when you might need to redo something again … and you’ll have something to read on a long winter evening when you can think up alternate ways solve the problems the bees create.

            Make sure you don’t divide and split the colony too much. Remember that getting a new queen mated and laying takes best part of a month during which time bee numbers will be dropping all the time. That new mated queen will need support when she starts laying strongly.

            Good luck

  3. Charlie Gerber

    In most beekeeping literature it says that the old queen leaves with the issuing trek swarm. This labels her as inferior , being old. In reality she is very good, having been able to build up a swarm to such an extend that they could make a natural split. I capture on average 800 trek swarms a year here in the northern part of South Africa on two nectar flows and very seldom find a trek swarm with an inferior queen. This bring us back to preventing swarming. It is my opinion that because we strive to have optimally big swarms we are doing exactly what is needed for swarming to happen. Trying to breed bees that is not prone to swarming is an exercise in futility. Making splits is the only way to successfully mimic nature and have at least the benefit of an additional swarm

    1. David Post author

      Hello Charlie

      I agree completely … a strong prime swarm is usually headed by a very good queen. She might well be ageing, but she’s proved her worth. I’m always delighted to have a big, strong, healthy prime swarm … not only might it generate a super or two of honey later in the year, but it’s also clearly got some good genes onboard.

      Temper can be an issue sometimes, but that (and disease, which may be present) are the only major downsides.


  4. Nigel Hurst

    Hi David, I have kept bees for about 23 years now. Over that time I have for one reason or another had to move quite a few of them short distances. I have tried various ideas including leaving an empty box on the old site and reuniting the returning bees with newspaper between the boxes . There turned out to be a very easy solution, in the evening go to the hive to be moved and stuff the entrance with grass. Move the hive to the new position leave for a few days until the grass starts to wither and the bees find there own way out. If they haven’t managed to clear the entrance after a few days, pull enough grass out for a couple of bees to get through. The bees realise something fairly dramatic has happened and they will reorientate themselves. Something else comes into play here as well as the amnesia thing , they don’t like leaving young brood, so a lot of the bees would probably stay when moving the hive . This method works well. When housing a swarm you can help keep them in by stuffing grass in the entrance too. This helps them settle and they are less likely to disappear the next day after hiving!

    1. David Post author

      Hello Nigel

      Those are certainly all useful tricks to relocate colonies/swarms intermediate distances. I didn’t have time/space to cover them having spent about 10 hours in the apiaries that day searching for queens and making up nucs. I was also trying to focus on the natural events of swarming per se, rather than on the ways beekeepers move established colonies about.

      Nuc entrance stuffed with grass

      I’ve noticed that hive entrances stuffed with grass act as a very effective way to knock pollen off the legs of returning foragers.

      Pollen trap

      Not of course an issue over the couple of days it’s in place.


  5. Chris Lloyd

    Good morning.
    Firstly, your articles are really useful and informative. Thank you.
    Secondly, your discussion above doesn’t mention small casts. I’m especially interested to know the originating conditions of these tiny swarms. I caught one this week – together with a proper swarm of around 10K bees on the same day – and they only occupy about two frames now they’ve settled in the hive. It was a bit irritating because really I should have put them in a nuk, but when I was told about the swarm I just grabbed a normal brood box and, once they were in, that was that. I caught a similar size swarm a few years ago and it never really took off and didn’t last the winter.
    I usually put a frame of honey in with a new colony to help them past that initial phase – would you recommend that or do you leave them to their own devices? I’m in Devon, so we don’t have the harsh climate your bees have to deal with. Usually. We do get a lot of wet though. It was awful this winter.

    1. David Post author

      Hello Chris

      It didn’t mention casts because it wasn’t about casts 😉

      If by ‘originating conditions’ you mean where do they come from? then that’s straightforward … they come from strong colonies that have reared multiple queens. The prime swarm with the mated queen goes first, taking a very significant proportion of the workers with her. A few days later the virgin Q’s emerge. These can then leave the hive, taking smaller and smaller numbers of bees with them. Some are little bigger than an orange when clustered. Two frames is a pretty good size for a cast.

      A colony will often generate several casts (if you’re unlucky the parent colony will effectively swarm itself to non-viability). If you can catch them you can bung them into the same box and let the queens sort out who will rule the roost. Individually, as you suggest, they often are too small to thrive. Personally, unless they were a good size, I’d remove the queen and shake them out in front of some strong colonies. The bees will find a home. I would not do this with a cast from an unknown hive … they might be carrying foulbroods.

      To avoid casts it is really important to only allow one new virgin queen to emerge. I’ve got a half-written post about this lurking in my drafts folder but am waiting on some pictures I hope to take this week.

      If there’s no nectar flow a swarm might well need supplementary feeding. Thin syrup to encourage comb building is probably best. Hooper recommends a gallon if the weather is poor. This makes sense – lots of mouths to feed, not stores and an urgent need to build comb.

      I’ve have discussed swarms and casts previously.


      1. vince poulin

        David – once again these posts have been valuable. You’ve given a lot of us such useful information. In your above response – it is bang-on. I commented earlier – had a very productive hive that threw a “prime-swarm”. I recaptured 1/3 of it and joined the with a NUC. The swarm hived (Yellow) was checked completely – I removed all visible QC’s (queen cells) building several new NUCs. To not loose our upcoming flow I gave the swarmed hive a young NUC (using newspaper) with a mated queen 5-days after the swarm. I checked before adding that NUC – no QC’s. 5-days after adding the NUC – I checked the hive. The new queen was in her box above the newspaper. Newspaper was now scattered, bees flowing between. I inspected the lower boxes (2). Lord – Box 2 – 4 hatched supercedure queen cells!!!!!! My jaw dropped. Holy Batman. I then spent a long time working through frames – no virgin queens. Did the new queen kill them? That afternoon – A SWARM! Swarm 2 – your cast swarm. Did the new queen leave or one of the virgin queens I did not find. I fretted for 3-days. Amazing but my new queen was still in the hive and thriving. Every nook and cranny filled with recently laid eggs. The cast swarm was off in a tall tree two houses from us. Your comments and understanding about swarming – has played out here. Luckily I did not loose my new queen. Looking at the process – for we urban keepers of bees managing swarm impulses is very challenging. Once we have more hives than we can deal with our options are limited. How many NUC’s can we manage especially when all of them are successful in raising the cells we give them. Must say though – 3-4 NUC’s provides enormous insurance. It is extremely satisfying to be able to react pro-actively to a lost queen especially when we raise them from kids.

        1. David Post author

          Hello Vince

          I’ve written previously about the stage during a beekeeper’s early years when they transition from too few bees to too many bees. In the early days we’re always worrying about getting queens mated and not losing swarms. With experience, although we may still be concerned about these things, we’re much better at keeping hives together and strong, or splitting at an appropriate time to increase stocks. Before too long we have too many bees to manage easily. For some that’s three hives, for others, 300. For me it’s about a dozen, but I usually seem to have about 20 🙁

          We also get better at understanding what went wrong (and how to rescue things) when it, inevitably, does … which I think is the topic for next week.


  6. Alan Deeley

    Dear David,
    What would you recommend as the minimum distance from an Apiary for the quarantine of a swarm?
    I collect swarms as a service to the community, and I routinely treat new swarms with Oxalic Acid vapour for varroa, but I am getting increasingly concerned about the potential virus load in a swarm, especially CBPV.
    You may recall that we are running an Apiary at Warwick University, and we have added a large 82msq extension separated by a 2m fence with debris netting. I’m worried this may not be enough and we may need a separate location altogether.

    Kind regards, Alan Deeley

    1. David Post author

      Hi Alan

      A colony heavily infested with CBPV is unlikely to swarm. It’s really pretty sick. Whether there are significant numbers of healthy carriers is an interesting question we are starting to tackle. It’s also not clear what role fomites play in disease transmission.

      If ‘healthy carriers’ are present in significant numbers I’d suggest that the distances involved would be the same as would apply to the foulbroods or any other disease. Samik Datta and colleagues (at Warwick) looked at American foulbrood transmission on Jersey – most was either owner-related (i.e. either moving infected bees between apiaries, or through use of contaminated equipment) or short distance transmission, usually less than a couple of kilometres. Although the latter might still have been beekeeper-mediated, it could also be due to bee to bee contamination. For example, through robbing or drifting either directly, or possibly through intermediate contact with feral colonies.

      Keith Delaplane and others have also looked at the relationship between drifting and distance. I’ve reviewed some of the literature previously. In these studies Varroa transmission occurred from colonies up to 1.5 kilometres away. I presume these were acquired by robbing, not drifting. I’ve tracked robbing bees across farmland to an apiary about a mile away.

      So, in answer to your question, a fence and an adjacent apiary are not going to stop bees moving between colonies in your main apiary and quarantine site. I’d definitely be looking for something situated further away (but know the area well and realise this might be a struggle – most of the fields have bees on them). Although one of the studies cited showed no reduction over distance, many do have an inverse relationship between drifting/robbing and distance … even a few hundred metres would likely make a big difference.

      You’re not going to find a site a mile away from other bees in your part of Warwickshire … I’d blame the local BKA for training so many enthusiastic and successful beekeepers 😉


  7. Eric Goulden

    Thank you David, you have answered many questions that I have. On behalf of beekeepers everywhere thank you for your very informative and educational articles

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