The size of a hive

I'm afraid that the title is a bit misleading. This post is more about the size - numerically - of the contents of the hive, rather than the hive itself, though that does get a mention. However, I fancied a rhyming title, and the only things I could think of to rhyme with colony was polony (a Bolognan sausage) or felony.

Neither really seemed appropriate.

Another title I considered, 'Live fast, die young', is related to the topic being covered, but provides the answer before the question {{1}}.

Which is ...

What determines 'the size of a hive' of honey bees?

It's not the hive, as most readers will be all too aware. You can house a colony in a hive that is too big without any real issues (at least in the warmer months), but a colony will quickly outgrow a hive that is physically too small.

The colony does not stop expanding once it has run out of space. Instead, it produces queen cells and swarms. Just think how much easier colony management would be if this wasn't the case.

But let's return to that colony housed in a box that's too big for it.

The colony expands, and expands, and expands ... but does this continue ad infinitum? If you simply provided your bees with an enormous box, or kept on adding boxes as the colony grew, would it prevent swarming, and would the colony keep getting more populous?

Yes ... but no.

Let's temporarily ignore the fact that honey bees are not immortal (because that is the primary topic of this post) so the population cannot expand forever.

Providing a growing colony with more space is a classic swarm prevention strategy, but they will eventually (almost certainly) make swarm preparations. Once the queen's pheromone levels are sufficiently dilute the colony will produce queen cells.

But, assuming they don't swarm, how big does the colony get?

It depends

There are a series of factors that determine the size of a colony. Some are obvious ... for example, a colony is larger in the summer months than it is in the winter.

This is the seasonal variation in colony size.

This occurs because the colony expands in Spring as forage becomes available, and the queen starts to lay more eggs. If it didn't expand, it wouldn't have a big enough population of workers to collect sufficient nectar to survive the following winter.

So perhaps the question should be, "What determines the maximum size a colony attains?"

We can consider the various factors involved as extrinsic or intrinsic; inevitably, the intrinsic ones are influenced - directly or indirectly - by the extrinsic ones.

Extrinsic factors

Temperature, nectar and pollen availability, together - at certain times - with the availability of water (or presence of rain) ... all of these things will impact the size of the colony.

All other things being equal, a colony in an area with good forage is likely to be larger than one in an area with poor forage.

At lower temperatures or if it is raining, even if forage is available, foraging might not be possible, or might only occur at limited times of the day, thereby limiting the size of the colony.

These are all pretty obvious and inevitably interrelated.

Moving quickly on ...

Intrinsic factors

These are the factors that directly influence the production of new bees and the loss of old bees from the colony.

The most obvious {{2}} of these intrinsic factors are:

• the rate at which new eggs are produced, and
• the longevity of worker bees (and, as you'll see, the rate at which they die)

Assuming the same worker lifespan, a colony headed by a queen laying more eggs per day will be larger than one in which egg production is more limited.

I'm going to ignore the queen and drones for the rest of the post. There's usually only one queen present and drone numbers - at least if you use frames with foundation - are managed at an artificially low level and comprise ~5% of the total population of the colony.

A picture is worth a thousand words

Except when it's one of my graphs ... but I'll have a go anyway.

Let's assume that - in late Spring and early Summer - the queen lays between 500 and 2,000 eggs per day. These are not unreasonable upper and lower limits {{3}}.

How long does a worker live?

Well, if you've attended one of my talks - or probably almost any talk in a beekeeping association - you'll have heard me glibly say something like:

Workers live about 6 weeks; spending the first 3 weeks as 'hive' bees and then becoming foragers for a further 3 weeks.

Does that sound familiar?

Assuming the queen lays at a steady state of 500 to 2,000 eggs per day, then the maximum total worker population is that number multiplied by the lifespan of a worker.

For convenience, I've done the calculations for you. If the queen lays 1,000 eggs per day and the resulting workers live exactly 6 weeks, then the adult worker population of the colony will be 42,000 (red line in Fig.1).

Conversely, a queen that only laid 500 eggs per day (green line) and whose workers only lived a month would create a colony numbering no more than 14,000 adult workers.

At the other end of the spectrum, a queen laying 2,000 eggs per day, with long-lived workers that survived for 8 weeks, would produce a colony numbering 112,000 (magenta line).

Caveats

Some of the eggs laid by the queen never hatch. Some hatch, but are dud. Both 'failures' are probably eaten. Likewise, some of the larvae die (and are eaten), or the pupae fail to emerge and are - all together now - eaten.

Waste not, want not.

There are losses at every stage. But, they're probably not huge, and they don't fundamentally alter the figures illustrated above.

Let's ignore them 😉.

Of course, the queen does not lay at a steady rate, day after day. However, trying to do the maths on fluctuating, or increasing or declining laying rates gets really messy {{4}} and adds little to the overall story.

Basically, the more eggs the queen lays per day, and the longer the lifespan of a worker bee, the larger the colony is.

My specialist subject ... the bleedin' obvious.

Sanity checking

Before I consider these colony sizes and whether they are realistic or not, let's do some sanity checking.

Our hives are a finite size.

They have 8, or 10, or 11 frames, or whatever ... and those frames provide an area of comb in which eggs are laid, the larvae are fed and the pupae, er, pupate.

How much of the available comb would be filled with 'brood in all stages' (eggs, larvae or pupae) at the laying rates used above.

At the highest laying rate - needed to produce the largest worker populations - is there sufficient comb in the hive to produce all those workers?

We can calculate this because the development cycle of workers is (effectively) invariant, and because we know the number of cells in a frame of drawn comb.

At least, I thought we did 😦.

Cells per frame and per hive

When I looked up these figures, they were all over the place. I won't cite all the sources, but here are a couple for starters.

Total brood cells in a National bee hive = 63,625

Worker cells = 50,000 (perhaps indirectly from the Thorne's catalogue which quotes the same number)

"Assume 25 worker cells per square inch of foundation" that measures 13.44 x 8 inches (and 11 frames in the box) = 59,000

So, to assuage my naturally rampant pedantry, I measured some Thorne's Premium worker brood foundation using the 'rhombus' method described by Allen Dick.

This foundation was a year or two old, but had been stored flat (near the top of the stack) and in a cool location.

I also measured the comb area (i.e. inside the woodwork of the frame) of a few of my standard National brood frames. These were 33.6 by 19 cm.

Then it was time to dust off the calculator and 'do the maths'.

If fully drawn, one face of a brood frame would have:

((33.6 x 19)/26.44) x 100 = 2,414 cells ...

Or 4,828 cells on both sides of one frame ...

Or 53,108 cells in a full brood box (i.e. 11 frames)

I've rounded the numbers down. These figures are all likely to be overestimates, as the frame is not a perfect multiple of cells wide or high.

Nevertheless, it's close enough for me, and it's a number I can trust as I measured it {{5}} .

The space occupied by 'brood in all stages'

So, assuming the queen lays at a constant rate of 500, 1,000, 1,500 or 2,000 eggs per day, how many cells will be occupied with 'brood in all stages', and what proportion of the total brood area available does this correspond to?

The numbers of eggs, larvae and pupae are simple to calculate - egg laying rate per day multiplied by the number of days of development at that stage, i.e. 3 for eggs, 5 for larvae and 13 for pupae.

So a queen laying at 500 eggs per day will produce 10,500 cells occupied with brood in all stages; 1,500 eggs, 2,500 larvae and 6,500 pupae.

These 10,500 cells is just ~20% {{6}} of the total cells available (the magenta line shows the percentage of comb occupied, on the right vertical axis).

Conversely, a queen laying 2,000 eggs per day will have brood in all stages occupying a total of 42,000 cells, which is about 79% of the available comb.

The latter figure is still some way short of the total number of brood cells in an 11 frame National hive ... but it's also more than I usually see in my hives.

What rate does a queen need to lay at to achieve the 18-20 'full' frames of brood you sometimes see claimed?

I'll leave that as an exercise for the reader 😉.

A quick reminder ... I'm ignoring cells occupied by drones, pollen, stores, those that are unoccupied, built wonky, over the wires etc.

Six weeks? Really?

So, a single brood box does have the capacity to produce the huge worker populations calculated.

But are these populations a reality?

No.

Colonies of managed honey bees do not contain 84,000 workers, let alone 112,000.

In fact, I'd be surprised if many colonies managed by amateur beekeepers in the UK contained more than 40,000 workers (the dotted line in the first graph).

It's not unusual to find 8, 9 or 10 frames of brood in all stages. Even though most are not more than ~75% full (the remaining space often being occupied by stores) that's still a lot of developing bees ... why are the colonies not bigger?

To generate that much brood the queen must be laying at a good clip ... therefore, the most likely explanation for the more modest size of the population is that worker bees do not live for 6 weeks.

Average lifespan

I'm not aware of any living thing that lives an exact period of time. Some live a little or a lot less, and some live a little or a lot more. The average of those lifespans is 6 weeks (bees {{7}}), ~80 years (humans, in the UK) or 1,500 - 2,000 years (the bristlecone pine {{8}}).

There are all sorts of ways to represent this range of ages around an average, but - typically - they create what is known as a bell-shaped curve.

So, does the average worker bee live 6 weeks?

No.

How long would the average worker lifespan need to be to produce a hive containing 30, 40, 50 or 60,000 bees?

That's a simple calculation of population divided by the eggs laid per day (or workers emerging per day).

For convenience {{9}}, I've indicated the average lifespan in days with the horizontal lines at week intervals. I've added a dotted line at 6 weeks.

Assuming no losses, a hive containing a queen laying 1,000 eggs per day, with workers that lived for almost 6 weeks (actually an average of 40 days) would have a worker population of 40,000 bees.

If she were laying 1,500 eggs a day, the workers would only need to live an average of 27 days to achieve the same population. If she was 'firing on all cylinders' and laying 2,000 eggs a day, an average worker lifespan of just 20 days would produce a colony 40,000 strong.

So how long is the average lifespan of a worker bee?

Not a bell shaped curve

This is where the 'Live fast, die young' title (that I didn't use) becomes relevant.

Most workers live much less than 6 weeks.

There are numerous studies of worker longevity, and the factors that influence it, e.g. flight activity, chronological age, extrinsic mortality or foraging specialisation (for example, see Rueppell et al., 2007).

Rather than get bogged down with those, I thought I'd briefly discuss two much simpler studies of worker age and longevity.

Jozef van der Steen and colleagues (van der Steen et al., 2012) marked hundreds of newly-emerged workers and then - every week - inspected colonies to determine their location in the hive {{10}} and - consequently - their survival.

This is relevant if you want a range of bees of different age classes ... 'pick a frame, any frame!'

Of the marked bees, only 41%, 23%, 17%, 11% and 8% were present after 1, 2, 3, 4 and 5 weeks respectively.

That means that 75% of workers that were marked disappeared within a fortnight, and over 90% had vanished by 5 weeks.

This study is not without fault; some of the older bees would have been out foraging, and the very early losses are higher than recorded in some other research, though apparently typical for work from this group.

Tagged bees survival study

More recently, Prado and colleagues (Prado et al., 2020) have used RFID tagging to monitor worker longevity. Over 3,000 bees were tagged and their activity - flying from and to the hive entrance - was recorded until death.

There was a short-lived population of workers that never became foragers. 40% died before 15 days of age, and 50% died before ever taking a foraging flight.

I don't know whether they were living fast, but they were certainly dying young.

Many of these bees likely died on orientation flights (these differ in duration from foraging flights, allowing a distinction to be made computationally).

Leaving the safe confines of the hive is a risky business.

Those that did mature into foragers experienced an average of 9% or 36% probability of death per hour or per day, respectively.

Those are pretty sobering numbers ... {{11}}. They also demonstratee that a forager only forages for part of the day.

The Prado study recorded the age bees first left the hive (~8.5-12 days) and the age at which they started foraging (~19.5-22.5 days). During the intervening period, those that survived were on orientation flights (and probably doing scouting duties as well).

Remember that quote about '3 weeks as hive bees and 3 weeks as foragers'? The Prado results provide a bit more granularity; those first three weeks are spent as hive bees and - after ~10 days - orientating to the environment outside the hive for a further ~10 days.

Then they become foragers ...

But most foragers perish within ~8 days (a figure in good agreement with an earlier study by Dukas and Visscher, 1994, and the 5 days quoted in another RFID-tagging study by Klein et al., 2019 that I've covered in a discussion of elite foragers).

Unsurprisingly, the later a worker takes her first flight, the longer she is expected to live.

In addition, and more interestingly, the greater the time that elapses between the first flight and the onset of foraging, the longer the overall expected lifespan.

Experience gained during orientation flights is clearly valuable.

Live fast, die young

Treat the numbers - at least any I generated - with caution. I've taken a lot of liberties in the name of 'simplification'. Some I mentioned in the text, others I have quietly ignored.

However, the numbers - even if rounded - provide some interesting insights into 'the size of the hive'.

In reverse order, a worker can expect to spend only about one week of her life as a forager, and ~3 weeks before that as a hive bee and learning about the environment around the hive.

Foraging is particularly risky; only about 50% of workers ever make a foraging flight. Those that do suffer a very high attrition rate.

Her overall longevity can be more than 4 weeks (from emergence) but typically is not.

Therefore, a colony with a queen laying 1,500 eggs per day might be expected to have a population significantly less than 42,000 bees (which would be the number expected if they all lived an average of 4 weeks; 28 x 1,500).

If you make some (more) arm-waving assumptions about the time at which 50% of the 'flying but not yet foraging' bees die, the number is more likely to be ~31,500.

For completeness, assuming the same life expectancy and 50% loss of orientating bees, queens laying at 500, 1,000 and 2,000 eggs per day would have hive populations of 10,500, 21,000 and 42,000 workers respectively.

Conclusions

The queen lays a lot of eggs ... she needs to.

Colonies must be strong to collect sufficient stores to overwinter, and they must also be strong to reproduce (swarm) successfully. Strong colonies overwinter better and can also defend the precious stores they have collected from being robbed in late summer.

Those facts alone dictate that the queen must lay a lot of eggs.

However, they are compounded by the very high losses of young workers within days of them first leaving the hive, and the subsequent very high mortality experienced by foragers during their short lifespan.

Live fast, die young and leave a good-looking corpse.

Entertaining? Informative? Useful? ... choose any three.
Please support further articles by becoming a sponsor or funding the caffeine that fuels my late night writing ...


Thank you

Notes

'Live fast, die young and leave a good-looking corpse' is a modern version of a quote originally attributed to Mrs. Irene B. Luce in a letter quoted (in 1920) during her divorce:

“I can’t be bothered with a husband,” one letter said.
“I intend to live a fast life, die young and be a beautiful corpse,” Mrs. Luce wrote.

References

Dukas, R., and Visscher, P.K. (1994) Lifetime learning by foraging honey bees. Animal Behaviour 48: 1007–1012 https://www.sciencedirect.com/science/article/pii/S0003347284713339.

Klein, S., Pasquaretta, C., He, X.J., Perry, C., Søvik, E., Devaud, J.-M., et al. (2019) Honey bees increase their foraging performance and frequency of pollen trips through experience. Sci Rep 9: 6778 https://www.nature.com/articles/s41598-019-42677-x.

Prado, A., Requier, F., Crauser, D., Le Conte, Y., Bretagnolle, V., and Alaux, C. (2020) Honeybee lifespan: the critical role of pre-foraging stage. Royal Society Open Science 7: 200998 https://royalsocietypublishing.org/doi/10.1098/rsos.200998.

Rueppell, O., Bachelier, C., Fondrk, M.K., and Page, R.E. (2007) Regulation of life history determines lifespan of worker honey bees (Apis mellifera L.). Experimental Gerontology 42: 1020–1032 https://www.sciencedirect.com/science/article/pii/S0531556507001313.

Steen, J.J.M. van der, Cornelissen, B., Donders, J., Blacquière, T., and Dooremalen, C. van (2012) How honey bees of successive age classes are distributed over a one storey, ten frames hive. Journal of Apicultural Research 51: 174–178 https://doi.org/10.3896/IBRA.1.51.2.05.

{{1}}: As usual, I ignored the AI-proposed clickbait offerings of 'The five essential things you need for beekeeping NOW!' or 'The ten errors most new beekeepers make'.

{{2}}: There are others; worker policing of eggs, brood diseases, genetics etc. ... all of which I'm going to ignore.

{{3}}: Which is why I chose them.

{{4}}: I'm already outside my comfort zone, mathematically speaking.

{{5}}: Though whether you should is a different matter.

{{6}}: Actually 19.77 and a bit percent, but I'm rounding all the numbers to improve readability.

{{7}}: Or, is it?

{{8}}: It's sometimes good to feel inferior.

{{9}}: Don't say I never do anything for you.

{{10}}: There was no difference - young bees were just as likely to be found on outer frames as the older bees.

{{11}}: At least, they are if you are a bee.