Theory of Swarming

The bee literature is full of discussions about swarming.  Many of them are about what to do about it with, as usual, as many opinions as there are opinionators.  I'm more interested in why it occurs so that I, and others, might be informed as to what, if anything, can be done about it.  The quick answer from the literature is that swarming is an instinctive behavior and the best one can do about it is live with it.  On the other hand there are many, many reports of attempts to stop it, some with reported success.

The scientific method starts with observations, proceeds to a hypothesis about what might be happening to produce those observations and moves on to a theory which is an attempt to explain all the observations in a rational manner and that also permits one to make predictions about observations not yet made.  It is in the success of explaining existing observations and making successful predictions that a theory gains credence.  In the physical sciences the theory is usually expressed as a mathematical formula of some sort but that doesn't usually work with life sciences.  Instead we have to rely on a heuristic method based upon rigorous logic but still allowing for "hunches" or "common sense."  Hence, such theories are never likely to please everyone but still might be useful to understand bee behavior a little bit better and to take action where needed in a more enlightened manner.

To list many, if not all, observations of bees that are reported in the literature (plus my own unpublished observations) I shall do without attribution.  Most readers of this piece will recognize them and accept them as fact.  The reader may comment on any or all, or cite missing examples that the theory should account for at the bottom of the page.

The first observation I want to mention is that, to my researches, the most common is that the bees appear to be "crowded" before swarming.  The most common advice I've found to prevent swarming is to prevent "crowding."  Just what crowding means needs to be explored and my attempts to do so were the origin of my thoughts to formulate this theory.  In particular, I asked "how does an individual bee 'know' that it is crowded?"  Before we come back to that let's list some more observations.

The bees start new queen cells and it is often reported that they start backfilling the brood nest with nectar and honey.  A good theory needs to explain this.  There are at least some pre-swarm observations needed to understand what is going on as well.  In particular, we need to understand the general process by which bees process and store honey which we accept as an evolutionary advantage to the species as a whole.  Among these observations are that the bees store honey above and "behind" the brood nest (there are statements in the literature that bees will not tolerate honey in or below the brood nest).

But the most cogent observation, to me, I can't find explicitly stated too often in the literature but is is fair, I think, to surmise it.  That is that a bee (at least a forager bee) will never pass up the opportunity to gather nectar and take it back to the hive.  The evolutionary advantages of this behavior should be clear.  So, following the path of the nectar leads to the theory of swarming.

It has been observed that foragers returning to the hive with a full load of nectar transfer it to hive bees of a certain age and return to the fields for more.  The hive bees "process" the nectar by adding components from their bodies to it and then deposit it in cells for ripening (removal of excess water which is accomplished by passing a breeze generated by the wings of others over the nectar).  This seems to be a well understood process.

But what happens if there are no cells in which the nectar-swollen bee can deposit her load?  IE, all the cells in the hive are occupied with honey or brood.  That this can happen is obvious and begins to explain the concept of "crowded."  It is not likely that such a bee would regurgitate her precious load and allow it to go to waste just to make her more comfortable (no evolutionary advantage there).  Instead, she will most likely simply wait and, during this wait, will start to digest the contents of her stomach(s).  The result of this would be - wax production.  With the production of wax, the problem of not enough cells in the hive becomes solvable and one can see a clear evolutionary advantage here.

This also accounts for other the observation that bees only draw comb when nectar (or sugar water) is coming in and the observation that bees "gorge" themselves on honey in order to make wax.  I cannot imagine that any given bee would decide that it is necessary to gorge herself for the good of the colony but if, in doing her instinctive job, she may find herself so gorged the overall effect is produced for the good of the colony as a whole.

Now, if we have a strong hive (ie, lots of foragers) and a strong nectar flow (ie, plenty of nectar to be gathered) we can see that a situation wherein the foragers are bringing in more nectar than can be stored in available cells can arise.  All of the processing bees can get sated and, when that happens the returning foragers will be unable to unload so will, presumably have to stop their foraging.  This could put a lot of bees in an uncomfortable, unhappy state and one can understand that a group decision to leave and find another home could build to a crescendo.

We also need to pay attention to the queen during these times.  If all the cells are full of honey or brood she can't lay and, presumably, must wait for the cohort of eggs laid 21 days earlier to emerge and free up some cells.  This number of cells equals her daily laying capacity and it would take her a whole day to fill them up again.  But there are many, possibly thousands, of bees full of nectar waiting to deposit their loads in an empty cell and they could probably  fill all those newly vacated cells in minutes (ie, the brood nest becomes backfilled).  The queen doesn't stand a chance.  So the queen is likely to be frustrated and unhappy, too, along with all the worker bees who are full of nectar with no place to put it.  This is a recipe for swarming.

We might also speculate that as the queen is forced to stop laying she emits some sort of distress signal (pheromone or other) that the workers interpret as a failing queen and they start "swarm" cells which might actually be supersedure cells (I doubt that the bees label them either way).  At this point, all the literature agrees that swarming is unavoidable.

We also note that there is no need for the swarmers to gorge on honey in preparation for their flight - they are already full and that is the root cause of the impetus to swarm.  It also means that the swarm will consist of foragers and hive bees capable of producing wax and making comb in their new home.

I believe this theory explains all the observed facts of swarming and may permit some more detailed observations not yet made.  But the practical application seems to be merely to reinforce the recommendations of old to give the bees enough room to satisfy their needs and they won't swarm (as likely).