Tag Archives: Karl von Frisch

Making a beeline

Synopsis : Honey bees use a range of navigation skills including path integration – to shorten return flights – combined with map-like spatial memories to relocate the hive.

Introduction

Regular readers will be aware that I’m interested in the origins of words. The Oxford English Dictionary (OED) is a fantastic source of information and produces a free Word of the Day email 1. This includes both the meaning and etymology of one word each day.

Since the complete dictionary includes over 600,000 words it will take a few years to collate the 20 volumes that comprise the entire dictionary 2.

At the beginning of this week the word of the day was beeline.

The word beeline of course means:

A straight line or course, such as a bee follows in returning to its hive after having collected a full load of nectar; (occasionally) the course taken by a bee.

The word originated in the US almost 200 years ago. It was first recorded in the American Quarterly Review in June 1828. Anyone who has read Tom Seeley’s Following the Wild Bees will appreciate the context in which the word beeline was used:

The bee-hunter..encloses them [sc. bees] in a tube, and letting one fly, marks its course, by a pocket compass. Departing to some distance, at right angles to the bee-line just ascertained, he liberates another, observes its course, and thus determines the position of the hive, which lies in the angle made by the intersection of the bee-lines.

Beelining is the art of finding feral or wild colonies by following the returning flight of bees. The book has a companion website with some interesting videos if you’d like to know more.

Find and tell

Beelining ‘works’ because bees fly in a straight line back to the nest 3.

The basics of beelining

Assume the blue flowers above are nectar-rich and favoured by the bees. You capture a couple of bees feeding on the blue flowers and give them some additional syrup so that they are replete and need to return to the colony to unload.

When you release the bees at ‘A’ they fly at a particular bearing back to the colony. However, if you instead release them at ‘B’ they fly at a different compass bearing back to the colony.4  .

How did the bees find the nectar-rich blue flowers in the first place?

Perhaps they observed another worker in the colony performing the waggle dance which informed them of the angle (from the sun) and distance to the blue flowers?

Alternatively, they might have just been searching around and chanced upon the blue flowers … they didn’t know they were there in the first place.

If they found the blue flowers by interpreting the waggle dance then you should be thinking how the waggle dancing bee found the blue flowers.

Alternatively, if they found the blue flowers by chance then you should be wondering how they will communicate their location to other foragers in the colony.

Transient nectar sources

Nectar sources are transient. They yield at particular times of the year … and of the day. The nectar may be dependent on recent rainfall or a variety of other environmental conditions.

All this means is that foragers may have to search widely to find a good source of nectar. If the source is really good – ample sugar-rich nectar and with lots of flowers producing it – then it’s important that the forager that found it tells her half-sisters how to also quickly find the same source.

Foraging and finding

On the left the blue flowers have been yielding for days. The workers fly there in a straight line and return along the same path. Newly orientated workers observe the returning foragers waggle dancing and follow the same route to quickly and efficiently exploit the source.

But all good things come to an end …

On the right is what happens when blue flowers stop yielding. The foragers that arrive at the blue flowers find slim pickings and start casting about looking for a better source of nectar. They first find the marginally better yellow flowers, then the similar (but far from outstanding) purple flowers … so they keep looking.

And eventually, they find the red flowers. Lots of nectar and lots of flowers. They load up and return directly to the colony (black dotted line).

There are two striking things about this return flight. The first is that it does not follow (in reverse) the route by which they reached the red flowers. The second is that when these returning foragers perform the waggle dance they ‘instruct’ the observing bees to fly in the direction of the red dotted line … rather than to the blue, then yellow, then purple and then red flowers.

Path integration

The foragers who find the red flowers perform a process termed path integration to return:

Path integration is the process by which an animal, when moving away from a start point, often its nest, cumulatively sums its path, generating an internal vector that specifies the line from the animal’s current position back to the start point, however circuitous the outward trip (Collet, 2019).

This is a skill I singularly lack when trying to relocate my vehicle in the multi-storey car park.

Path integration is seen in other insects … Drosophila fruit flies can do it (over a range of centimetres), walking ants can do it over a range of hundreds of metres, and honey bees can do it over at least 5 kilometres (and probably more).

Path integration requires two pieces of information – the direction and the distance of travel.

Path integration – individual parts of the flight are in different directions and of different lengths

Clearly, the very existence of the waggle dance provides compelling evidence that bees are aware of both. The dancing forager reports the angle (relative to the sun) of the nectar source and the distance at that angle that must be covered before the nectar source is located.

But for path integration, not only must the angle and distances be determined, they must also be cumulatively summed.

Neurophysiology and evolutionary conservation

Detailed neurophysiological experiments – recording the firing of individual neurones in the bee’s brain – have identified that these events occur in a region called the central complex (CX).

Two types of neurones are involved; the first is a set of polarised-light-based compass neurones and the second are optic-flow-based speed neurones. The former use celestial cues to create a visual compass. The latter provide a visual odometer (Stone et al., 2017).

Together – and there are additional integrator cells that link these functions – this relatively simple 5 neuronal circuitry allows path integration, enabling the bee to return ‘home’ directly after a convoluted outward flight.

Many of these studies were conducted on the nocturnal sweat bee Megalopta genalis. This forages at night when polarised skylight provides the directional cues in its rainforest habitat.

Importantly, similar neuronal organisation is found in the CX’s of locusts, some butterflies and dung beetles. The visual odometer neurones were analysed in Megalopta genalis, but are physically and likely functionally similar to structures found in Bombus terrestris (a bumble bee).

You may have noticed that none of these studies used our favourite, Apis mellifera, the honey bee.

The evolution of termites, ants, wasps and bees

Nevertheless, there’s every reason to think that honey bee path integration involves very similar neuronal activity. Megalopta (belonging to the family Halictidae) and Bombus (a member of the Apidae family) are very distantly related and evolved from a common ancestor over 100 million years ago (Cardinal and Danforth, 2011). It’s therefore likely that all bees derived from this common ancestor – including honey bees – share similar neuronal activity underpinning their path integration ability.

Food vectors

Before considering another point about honey bee flight I wanted to to briefly mention features of the outbound trip back to the high quality food source (the red dotted line in diagram above). This is termed the food vector and is essentially the reverse of the path integrated return flight back to the colony i.e. the same length, but pointing in the opposite direction.

The waggle dance communicates this food vector to nest mates of the successful returning forager.

But what happens if bees are displaced when starting, or while following this food vector?

For example, if a huge gust of wind blew them off course by tens or hundreds of metres, or an evil eager scientist captured them as they left the hive and transported them in a dark box across a couple of fields and then released them?

Where do displaced foragers go?

Do the bees fly a corrected route to the food source (the blue dotted arrow), or do they continue flying the same vector (angle and distance – the green dotted arrow) they would have done when they left the hive?

I’m not sure this exact experiment has been done with bees (but see below), but it has been done with ants (Cataglyphis fortis). In these studies the ’displaced’ ants did alter their direction of travel (Collett et al., 1999). The food vector is more than just an angle and distance, it also points to a position relative to the nest. The redirection exhibited by the ants was not perfect, but it clearly showed they were able to integrate the path to a location other than the nest after displacement.

Gusts of wind are not the same as eager scientists

However, back to the bees.

The gust of wind and eager scientist are not equivalent. Bees cope with gusts of wind every day. It always amazes me how well bees cope on windy days.

When blown off course they will get lots of visual cues – not least changes in optic flow and their angle to the sun – both of which should be readily corrected. If they didn’t then foragers would be lost in droves on windy days … or fail to find the food source.

In contrast, the eager scientist took care to place the bees in a darkened box, thereby immediately removing visual cues such as the angle of the sun and the optic flow.

In the studies conducted with the ants the scientists made sure the ants could see the sky but not the surrounding landscape (they trained them in open topped channels). This is because ants can also use landmarks in the surrounding landscape for orientation 6.

And bees can do the same, which is the final sub-topic for this post on bee flight and orientation.

The map-like spatial memory of bees

Path integration is both useful and necessary. It means that foragers can return – fully laden – with minimum delay to the hive. They can therefore tell other foragers (via waggle dancing) promptly, and – in the case of elite foragers – they can set off again on another trip.

By reducing the distance flown – by integrating the path – they save not only time but ‘fuel’ as well i.e. path integration allows bees to maximise the nectar returned at the end of the foraging trip.

But, if all flights were a combination of random searches and path-integrated returns, why do bees go on orientation flights?

Orientation flights are short range (10’s to 100’s of metres) flights around the hive. These are taken by workers around 3 weeks after emergence as they transition form hive bees to foragers. They are also taken by older foragers if the hive is moved.

The very existence of orientation flights is compelling evidence that honey bees also use learned environmental landmarks for route finding, or at least for mapping the area around the hive to aid efficient return trips.

What evidence is there that these landmarks are used for this purpose?

Harmonic radar tracking of displaced foragers

I’ve previously discussed the use of short range harmonic radar to track bees ‘tagged’ with a small transponder. The key point is that it allows relatively accurate mapping of the entire flight of a bee up to 900 metres away. The resolution is, at best, about 3 metres.

Menzel and colleagues (Menzel et al., 2004) tracked the flights of three types of ‘displaced’ foragers:

  • SF-bees trained to a stationary feeder a few hundred metres from the hive; these have ‘route memory’ and have traversed the route from the hive to the feeder multiple times
  • VF-bees trained to a regularly moved feeder within 10 metres of the hive; these bees have no route memory
  • R-bees which were recruited by a waggle dancing forager and have only secondhand route information of the position of the feeder i.e. they have never made the trip themselves

These are not trivial experiments. To ensure the environment was as uniform as possible they conducted the experiments in a large, flat mown field approximately 800 metres square. There was no forage within the field other than the experimental feeders. The field was surrounded on all sides by uniform coniferous woodland with insufficient variation in elevation (<1.5°) above the horizontal to provide any visual clues to the bees.

The field itself was not uniform. There were differences due to different mowing times and soil conditions. In addition, the scientists erected a number of radar-transparent coloured tents around the hive to provide additional landmarks.

Common features of flight paths determined by harmonic radar studies

Bees were allowed to orientate to the new hive position and then SF- and VF-bees were collected at a feeder and R-bees were captured as they left the observation hive (having ‘watched’ a waggle dance). The bees were fitted with a transponder, released some distance away from the feeder or the hive and then tracked by radar.

SF- and VF-bees were stuffed full of syrup and so – although they could fly for a long time – were motivated to return to the hive to unload their cargo. R-bees, whilst ‘primed’ to seek the feeder, had limited range and so would have to return to the hive to refuel.

Return flights of SF-, VF- and R-bees show some common features.

The SF- and R-bees exhibited three broadly conserved flight patterns during their return trip to the hive:

  1. A fast (20 m/s) straight line flight in the direction they would have taken back to the hive (for the SF-bees) or out to the feeder (for the R-bees). The length of this part of the flight was approximately the distance between the hive and the feeder.
  2. A slow (13 m/s) curved search flight.
  3. A fast homing flight back to the hive.

The VF-bees only exhibited the slow curved search flight and the final fast homing flight. This was unsurprising as they had never learned (or been told) to follow the route between the hive and distant feeder.

Food vectors and von Frisch

We therefore have the answer to the question I posed earlier (in the Food vector section above). A bee displaced when about to embark for the first time on a trip to a distant feeder – learnt from following a waggle dance – initially flies at the angle and to the approximate distance they would have taken from the hive (stage 1 of the flight).

Remember, unlike the ants, these foragers are ‘in the dark’ while being displaced, so have no visual clues about the displacement.

This is a really nice result and supports the contention made by von Frisch that the waggle dance communicates only distance and direction (relative to the sun) information, rather than positional information (von Frisch, 1967) 7.

Homeward bound

After a period of slow curved flights the returning forager switches to a direct, fast homing flight. These started at positions – starred in the figure above – from which the bee could not see the hive (based upon distance and the known resolution of honey bee vision).

Homing flights of displaced SF-, VF- and R-bees (A, B, C respectively). H indicates the position of the hive.

Individual bees were randomly displaced around the study field. The homing flights were in a straight(ish) line and bees approached the hive from a range of different points of the compass. This argues strongly against the bees following a particular feature on the ground that led them back to the hive.

Instead, the authors argue that, since all the bees exhibit these direct homing flights, it must be based upon previous exploratory memory i.e. from orientation flights.

The tents were not critical landmarks. If they were moved some distance away the bees still returned using the same three flight phases (in the case of SF- and R-bees) and with similar navigational performance. Clearly there was sufficient information in the ground structure alone (mowing patterns, soil differences) acquired during the orientation flights.

In support of this, some of the harmonic radar data showed bees flying along boundaries between mown areas (in a similar way to homing pigeons follow rivers or motorways; Guilford and Biro, 2014.).

These experiments indicate that during orientation flights the bee develops a local spatial memory of landmarks that provide a ‘memory map’. This enables the bee to return to the nest once it recognises some of these familiar landmarks.

Repeated displacement flights of the same bee further indicated that the landmarks recognised (whatever they were) could be approached from different angles.

Final inspections

My bees are still out foraging despite the large blocks of fondant most hives are now topped with. I’m not sure what they’re collecting but it’s clearly worth the trip … and going to the initial trouble of finding it and telling other foragers about it.

Returning foragers

We usually take the amazing navigational abilities of our bees for granted. Those returning foragers are using navigational skills that evolved at least 100 million years ago while dinosaurs roamed the earth.

100 million years is a long time to develop a range of skills and subtleties; it’s no wonder we still only partially understand honey bee navigation. Of course, we don’t have to understand it to still marvel at their ability to find the way back.

And it’s worth also remembering that these navigation skills – many of which are based upon the angle of travel relative to the direction of the sun – also operate on dull, overcast days. But that’s a topic for another post …


References

  • Cardinal, S. and Danforth, B.N. (2011) ‘The Antiquity and Evolutionary History of Social Behavior in Bees’, PLOS ONE, 6(6), p. e21086. Available at: https://doi.org/10.1371/journal.pone.0021086.
  • Collett, M., Collett, T.S. and Wehner, R. (1999) ‘Calibration of vector navigation in desert ants’, Current Biology, 9(18), pp. 1031–1034. Available at: https://doi.org/10.1016/S0960-9822(99)80451-5.
  • Guilford, T. and Biro, D. (2014) ‘Route following and the pigeon’s familiar area map’, Journal of Experimental Biology, 217(2), pp. 169–179. Available at: https://doi.org/10.1242/jeb.092908.
  • Menzel, R. et al. (2005) ‘Honey bees navigate according to a map-like spatial memory’, Proceedings of the National Academy of Sciences, 102(8), pp. 3040–3045. Available at: https://doi.org/10.1073/pnas.0408550102.
  • Stone, T. et al. (2017) ‘An Anatomically Constrained Model for Path Integration in the Bee Brain’, Current Biology, 27(20), pp. 3069-3085.e11. Available at: https://doi.org/10.1016/j.cub.2017.08.052.

Growing old (dis)gracefully

… but in this world nothing can be said to be certain, except death and taxes.

So wrote Benjamin Franklin in 1789 1.

Taxes are a subject that I’ve not previously covered. Furthermore, I have no intention of writing about them in the future. My once a year late-night wrestle with the HMRC website is a distressing enough experience and one I’d prefer not to be reminded about.

So this week I’ll deal with that other certainty … death.

Eilean Fhianain burial ground, Loch Shiel

Sooner or later it will happen to us all.

No ifs or buts, and – unlike taxes – it really is a certainty.

What’s interesting about death is the ‘sooner or later’ element.

Some die young, due to bad luck, poor health or overindulgence.

Others live to a ripe old age, outliving their peers by many years or even decades.

Talking the talk

Beekeeping has been a relatively solitary pastime for the last 16 months. The restrictions imposed by lockdowns and social distancing have meant that beekeeping meetings have all been ‘virtual’. 

I’ve written about these recently and it seems likely that many associations are going to continue (at least some of the time) with Zoom talks.

A caffeine-fueled Q&A session

Whether in person, or online, one of the things that’s noticeable is that all beekeeping audiences are – how can I put this delicately? – not as young as they used to be.

By which I mean the individual beekeepers are not callow youths, but are instead older, wiser, and – of course – better looking. 

In my experience, giving talks over the last decade or so, beekeeping audiences have always had an older average age than a cross-section of society.

In addition, as I briefly mentioned recently, the average age of beefarmers in the UK is about 66 years old.

Why is this?

It seems there are two possibilities:

  1. Since beekeeping takes a reasonable amount of time, it’s largely people who have more spare time who start or stick with the hobby. At least at the start, beekeeping also costs quite a bit of money. Again, those who are a bit older probably have more disposable income (or fewer distractions like mortgages or kids to spend it on).
  2. Beekeepers live longer. The relatively high average age of a beekeeping audience – when compared with a similarly-sized cross-section of society – reflects their increased longevity.

Of course, both of those are rather simplistic explanations, but it’s a start.

Do beekeepers live longer?

When you start beekeeping you tend to be interested in honey and swarm control and pathogens.

Or just honey 😉

But after a few years of successful beekeeping you probably produce quite a bit of honey. Your success in honey production is partly due to your understanding and implementation of swarm control, and by your interventions that minimise disease.

And so your interests in beekeeping expand.

Some produce award-winning candles or wax flowers, some rear hundreds of queens a season, some explore esoteric hive designs, and some become interested in the history of beekeeping.

And one of the things that’s noticeable about the history of beekeeping is that several well known beekeepers lived to a remarkably old age.

With improvements in nutrition and healthcare, the average life expectancy of the population has been increasing for the last 150 years or so. 

UK life expectancy (from birth) 1765-2020

If you were born in the 18th Century you’d be expected to live (on average) about 40 years. However, in the last third of the 19th Century, life expectancy started to increase.

I was going to say ‘inexorably increase’ were it not for that little blip around 1918-1920. That wasn’t the First World War. It was the last significant global viral pandemic, the so-called Spanish ‘flu 2. Only recently has this increase in life expectancy started to plateau, and actually reverse.

Well known historical (old) beekeepers

My knowledge of the history of beekeeping is rather patchy so I did a quick search for ‘famous beekeepers‘.

Don’t bother with the first couple of hits 3, but the third is the ever-dependable and enjoyable Bad Beekeeping Blog by Ron Miksha.

Here’s a few picked at anything-but-random ( 😉 ) to support my hypothesis that beekeepers live longer. 

In no particular order:

  • François Huber (1750-1831, 81 years), Swiss, ~40 years 4. Huber was an extraordinary individual 5. Despite being blind his ‘observations’ worked out many details of the life cycle of the queen and he developed one of the first observation hives.
  • Lorenzo Langstroth (1810-1895, 85 years), US, ~40 years. Langstroth combined an understanding of ‘bee space’ with the movable frame ‘leaf hive’ (developed by Huber) to develop and patent the first removable frame hive.
  • Brother Adam (1898-1996, 98 years), German (lived in UK), ~47 years. Brother Adam (Karl Kehrle) was an authority on bee breeding and the developer of the Buckfast strain of honey bees. He resigned his post of beekeeper at Buckfast Abbey at the age of 93.
  • Charles Dadant (1817-1902, 85 years), French (lived in US), ~40 years. Dadant invented the Dadant hive, ran thousands of hives (after failing as a vintner) and founded the – still flourishing – Dadant & Sons beekeeping business.
  • Eva Crane (1912-2007, 95 years), UK, ~52 years. Eva Crane was a mathematician/physicist who spent much of her (long) life doing research on bees. She founded the Bee Research Association (still flourishing as the International Bee Research Association) and wrote hundreds of papers, and notable books, on bees and beekeeping.
  • Harry Laidlaw (1907-2003, 96 years), US, ~51 years. Harry Laidlaw was one of the pioneers of studies on bee genetics and optimised methods for instrumental insemination of queens. 
  • Karl von Frisch (1886-1982, 96 years), German, ~39 years. Karl von Frisch deciphered the waggle dance of honey bees and received the Nobel Prize in 1973.

And there are many others … including many much less famous but equally old 6

Correlation not causation

Just because (some) beekeepers live a long time doesn’t mean that beekeeping is responsible for their longevity. 

Perhaps they’ve just got ‘good genes’ and they’d have lived into their 80’s or 90’s whether they’d been beekeepers or BASE jumpers.

BASE jumping, Half Dome, Yosemite

Maybe it takes that long to become an acknowledged expert at beekeeping? 

How many famous beekeepers can you name who died young?

If Harry Laidlaw had only lived to his mid-60’s (still older than the average for his year of birth) perhaps he’d have been unknown?

Unlikely … he published his first book at the age of 25, was elected a fellow of the American Association for the Advancement of Science at 48 and was the first Associate Dean for Research in UC Davis in his late 50’s.

All of the individuals listed enjoyed a near-lifelong association with bees and were clearly exceptional beekeepers well before they also achieved an exceptional age (considering the year that they were born).

So perhaps there is something about bees or beekeeping that makes beekeepers live longer?

One possibility is that honey is good for you. 

Although some beekeepers don’t like honey 7, most undoubtedly do. Honey has a host of antimicrobial, antiviral, antiparasitic, anti-inflammatory and antioxidant effects, as well as being a guaranteed ( 😉 ) way to prevent hay fever.

Or perhaps it’s bee stings? 8

Caveat

Treat most of what I’ve written above with some caution.

My selection of famous (old) beekeepers is extremely selective. 

The reason audiences in beekeeping association meetings have a high average age is almost certainly due to spare time and disposable incomes … and because all the young ones are out partying.

It’s not my sort of science, but a proper study of the association between longevity and beekeeping would be quite interesting. 

Do beekeepers actually live longer than non beekeepers? 

Is there a causative association? Is it associated with beekeeping per se, or do non-beekeepers who eat honey also live longer? How many hive/years do you need to keep bees to increase your longevity? If it’s bee stings that are beneficial, do beekeepers who keep stingless bees also live long and healthy lives?

There is literally a certain finality about studying the age at death. Are there perhaps other markers of longevity that could be investigated a little earlier in a beekeeper’s life?

There certainly are …

Chromosomes and DNA replication

We (beekeepers) have 23 pairs of chromosomes 9 that consist of DNA and proteins and contain the majority of our genetic material 10

The chromosomes are in nucleus of the cell.

Cells associate to form tissue (like muscle or nerves) which associate to form organs (like the heart or brain).

As humans grow – from egg, to embryo, to foetus, to adult – these cells have to divide. And the chromosomes have to be duplicated to ensure that all cells end up with the required 23 pairs. 

Chromosomes are not circular but are essentially linear strands of DNA. This introduces a problem. 

The enzymes that copy and make new DNA (the DNA polymerase) only ‘work’ in one direction. Since DNA consists of two antiparallel strands this means that the polymerase copies one strand directly to make one continuous product, but it copies the other strand in small pieces, and then joins them together. 

The details really don’t matter … but the consequences do. 

The small piece synthesised at the very end of the discontinuously copied strand isn’t quite at the very end of the strand 11

Frankly, this is a bit of a design flaw 🙁

Telomeres

As a consequence of this discontinuous copying, one of the strands of the DNA molecule gets a little bit shorter every time it is copied.

The DNA of chromosomes contains all the genes that make all the proteins that makes all the cells that get together to form all the tissues that create the organs that make beekeepers.

Phew!

So, if the little bit of the chromosome that’s lost during replication happened to contain an essential gene, things would go very seriously wrong™.

But chromosomes have a sort of ‘get out of jail card’.

The ends of the chromosome contain a region of highly repetitive and non-coding 12 DNA called telomeres. You can imagine the telomere as a sort of ‘cap’ at the end of the chromosome.

During replication, little bits of this cap are lost – the cap gets shorter – but this truncation does not result in the loss of any essential genes.

Telomere shortening and cell division

And all this telomere shortening is rather predictable.

As cells divide – during growth or tissue repair – the telomeres shorten. Therefore, if you measure telomere length you can get an idea of how many division it has undergone and therefore how old it is.

Telomere length is therefore a measure of biological age.

Except it’s not quite that simple

There are a bunch of things that also influence telomere length.

For example, the age of the father influences the length of the child’s telomeres. 

Telomeres also accumulate damage – and so shorten – through oxidative stress. This is a process that results from the excess production of oxidants such as peroxides, free radicals and reactive oxygen species. These are chemical intermediates in normal biochemical processes. The cell can cope with small amounts of oxidants. However, the protection mechanisms become swamped if they are in excess, resulting in cellular damage.

Some diets are rich in antioxidants which can (or at least are hypothesised to) reduce oxidative stress. 

Honey can contain high levels of polyphenols, these are well known antioxidants that are also found in some fruits, vegetables and olive oil.

Finally … we’re getting somewhere 😉

There are studies that demonstrate that eating honey every day increases the levels of antioxidants 13. However, I’m not aware that these or other studies were extended to investigate whether the test cohort also exhibited a reduced rate of telomere shortening.

This isn’t surprising … the inherent variation between individuals and the relatively slow rate at which telomeres shorten means thousands of individuals would need to be analysed. Potentially over many years.

But there is also a study of telomere length in beekeepers … which is the reason for the 2,200 word introduction above.

Beekeepers and telomeres

A Malaysian research team 14 have measured telomere length in 30 beekeepers and the same number of age-matched non-beekeepers.

The beekeepers chosen had all been keeping bees for at least five years. The non-beekeepers didn’t just not keep bees 15, they also did not consume any bee products (honey, propolis 16 or royal jelly 17 ). In addition to being age-matched (average age ~42 years) both groups excluded individuals with known disease.

And I wouldn’t have been telling you all this unless the telomere length did differ significantly. The non-beekeeper’s had telomeres that were ~30% shorter.

Chronologically they were the same age, but biologically they were older.

This small study also investigated whether there was a correlation between the period of beekeeping, the number of bee products consumed, or the period or frequency of bee product consumption, and telomere length.

Telomere length only correlated with the frequency and duration of consumption of bee products, not with the types of products or the number of years of beekeeping.

The significance of these sorts of population-based studies is related to the scale of the study. This is a small study, and the only one I’m aware of that specifically investigates telomere length in beekeepers.

It has only been cited 7 times and has not been repeated.

It remains firmly in the ‘interesting observation’ rather than ‘acknowledged fact’ category. 

So all those afternoons hunched over the hive appear to make no difference 18, but having honey every day on your porridge might actually make you younger.

Biologically younger … you’ll still look old 😉


 

Going the distance

I’m going to continue with a topic related to the waggle dance this week.

This is partly so I can write about the science of how bees measure distance to a food source.

But it’s also to encourage those who didn’t read the waggle dance post to visit it. Weirdly it was only read by about 50% of the usual Friday/weekend readership and I suspect (from a couple of emails I received) that the weekly post to subscribers ended up in spam folders 1.

If you remember, the duration of the waggle phase of the dance – the straight-line abdomen-wiggling sashay across the ‘dance floor’ – indicates the distance from the nest to the desirable food source 2. The vigour of the wiggle indicates the quality of the source.

How do bees measure distance?

Karl von Frisch, the first to decode the waggle dance, favoured the so-called ‘energy hypothesis’. In this, the distance to a food source was determined by the amount of energy used on the outbound flight.

Does that seem logical?

Foragers forage randomly, but usually return directly

If correct, foragers would only be able to determine the energy used after their second trip to a food source. This presumes their first trip was longer as they searched the environment for something worth dancing about 3.

This would be an easy thing to test, though I’m not sure it was ever investigated 4.

As it happens, far better brains determined that the energy hypothesis was probably incorrect. Many of these studies explored how gravity influences the distances reported by dancing foragers.

Going up!

Bees use more energy when flying up. For example, when flying from ground level to the top of a tall building, when compared to level flight. Similarly, they use more energy flying if they have small weights attached to them 5.

A series of experiments, nicely reviewed by Harald Esch and John Burns 6, failed to provide good support for the energy hypothesis. There were lots of these studies, involving steep mountains, tall buildings or balloons, between the 1950’s and mid-80’s.

Interesting science, and no doubt it was a lot of fun doing the experiments.

For example, bees flying to a sugar feeder situated on top of a tall building dance to ‘report’ the same distance as bees from the same hive flying to a feeder at ground level adjacent to the same building.

Similarly, foragers loaded with weights do not overestimate the distance to a food source, as would be expected if the energy expended to reach it was being measured 7.

Interesting and entertaining science certainly, but none of it providing compelling support for the energy hypothesis

It’s notable that there is a rather telling sentence from the Esch & Burns review that states “While reading the original papers, one gains the impression that evidence supporting the energy hypothesis was favored over arguments against it”.

Ouch!

Splash landing

Although Von Frisch was a supporter of the energy hypothesis 8 he also published a study that provided evidence for our current understanding of how bees measure distance.

Bees generally don’t like flying long distances over water. Von Frisch provided two equidistant nectar sources, one of which was situated on the other side of a lake.

Bees flying over calm water underestimate distances

On very calm days the bees that flew across the lake under-reported the distance to the feeder. This underestimate was by 20-25% when compared to bees flying to an equidistant feeder overland.

Von Frisch commented “the bee’s estimation of distance is not determined through optical examination of the surface beneath her”.

He assumed that the mirror-like water surface provided no optical input as it contained no visual ‘clues’. After all, one calm patch of water looks much like any other. Von Frisch used this as an argument for the energy hypothesis.

He also noted that the bees generally flew very low over the water surface, often so low that they drowned 🙁

Perhaps these bees were flying dangerously low to try and find optical clues.

Such as their height above the surface?

Or perhaps the distance travelled?

Going with the flow

Having debunked the energy hypothesis, Esch & Burns proposed instead the optic flow hypothesis. This states that “foragers use the retinal image flow of ground motion to gauge feeder distance”.

Imagine optic flow as tripping a little odometer in the bee brain that records distance as her eyes observe the environment flashing past during flight. The clever thing about that is that the environment is variable. It’s not like counting off regularly spaced telegraph poles from a train window.

When flying, environmental objects that are nearby will move across her vision much faster than distant objects. Bees don’t have stereo vision, but instead use this speed of image motion to infer range.

Optic flow – the arrow size indicates the speed with which the object apparently moves, and hence its range

Esch & Burns returned again to tall buildings to provide supporting evidence for their optic flow hypothesis. They trained bees to fly between two tall buildings with 228 metres separating the hive and the feeder 9.

Returning foragers reported that the food source was only 125 metres away.

However, the bees didn’t make a direct flight. Instead they flew at altitude for 30-50 metres, descended to fly much lower, then ascended again to approach the feeder again at altitude.

Esch & Burns experiment to support the optic flow hypothesis

The interpretation here was that the high altitude flight provided insufficient optic flow to measure distance. The bees descend to get the visual input needed to judge distance, but it’s only for part of the flight … hence leading to under-reporting the distance separating the hive and feeder.

Tunnel vision

Jurgen Tautz 10 and colleagues trained bees to forage in a short, narrow tunnel 11. This elegant experiment provided compelling support for the optic flow hypothesis.

The tunnel was ~6 m long and with a cross sectional area of ~200 cm2 – big enough for a bee to fly along, but sufficiently narrow so that the bee would be closer to the ‘walls’ than in normal free flight. The walls and floor of the tunnel had a random visual texture. Only the end of the tunnel facing the hive was open.

The tunnel experiment.

These studies were conducted when the terms round and waggle were used to distinguish the dance induced by food sources <50 m and >50 m respectively from the hive 12. Rather than emphasise the shape of the dance I’ll just describe it as a >50 m or <50 m waggle dance.

‘Tunneling’ bees misreport distances

In the first tunnel experiment (1) the feeder was 35 m from the hive. 85% of dances indicated the feeder was <50 m away. However, when the feeder was moved to the opposite end of the tunnel (2) – still only 41 m from the hive – 90% of the dances indicated the feeder was >50 m away.

To test how the random pattern influenced the perceived distance the scientists used a third tunnel (3) lined with lengthwise stripes. In this instance – despite the feeder position being unchanged from experiment 2 – 90% of the dances indicated the feeder was <50 m away.

The stripes were predicted to ‘work’ in the same way as the smooth lake surface, providing no visual clues.

In the fourth experiment (4) the feeder was 6 m along a randomly patterned tunnel, which was placed just 6 m from the hive. Over 87% of dances indicated that the feeder was >50 m away.

Interpreting the waggle run

In open flight 13 there is usually an excellent correlation between the duration of the waggle run and the distance to a feeder (see the graph below 14 ). By extrapolation, the bees in experiments 2 and 4 ‘thought’ they had flown 230 m and 184 m respectively. In reality they had flown only 41 m and 12 m in these experiments.

Determining distances from waggle dance observation

How could the bees get it so wrong?

Increased optic flow

Tunnel-traversing bees fly just a few centimeters away from the visible ‘environment’.

As a consequence, at the same flight speed, they experience greater optic flow.

If, instead of driving around in your lumbering old van, you pack your hive tool in a Caterham 7 for the trip to the apiary you’d be well aware of what I mean.

Caterham 7 … check out that optic flow … then make another trip to collect the smoker

30 mph in a Toyota Hilux feels very much slower than 30 mph in a Caterham 7. This is largely because visual reference points, like the broken white lines between lanes in the road, appear in and disappear from your field of view much faster … because you’re much closer to them.

Because the tunnel dimensions were known it was possible to calculate the calibration of the bee’s odometer. Classically this would be defined in terms of metres of distance flown generating a particular waggle run length or duration.

These tunnel studies demonstrate that distance flown is not what calibrates the odometer. Instead it’s quantified indirectly in terms of the image motion experienced by the eye. Since environments vary the way to express this is the amount of angular image motion that generates a given duration of waggle.

And, using some mathematical trickery we don’t need to bother with 15, it turns out that this angular motion is only dependent upon distance flown, not the speed of flight.

This is important. Headwinds or tailwinds could change the speed of flight, but not the distance flown 16.

It’s all relative

It’s worth emphasising that the dance followers in experiments 2 (above) should still find the feeder.

The waggle dance would ‘instruct’ them to fly 230 m at the bearing indicated and they’d experience the same visual clues en route.

This means that they should still enter the narrow tunnel and experience increased optic flow because of the encroaching walls. But they’d be experiencing the same optic flow the initial dancing bee had experienced, so would not attempt to fly further down the tunnel.

This means that the optic flow experienced is context dependent. It is related to the environment the bees are foraging in.

This makes sense as the dancing bees and dance followers all occupy the same environment.

How do we know this? 17

Changing the environment

If we change the environment the dance followers search at the wrong distance.

I qualified the statement above when I said that the dance followers should still enter the tunnel and find the feeder.

Actually, most recruits will miss the tunnel entrance – remember it’s smaller that a sheet of A5 paper. At 35 m distance a bee would have to get the bearing correct to about 0.16° to enter the tunnel 18.

So the bees that do not enter the tunnel experience a different environment.

Where do they search for the feeder?

They search at the distance indicated by the waggle duration … so bees that missed the tunnel entrance in experiment 2 (above) would have searched for the feeder 230 m from the hive. Similarly, the dance followers in experiment 4 would have searched 184 m away 19

Context dependent dance calibration

And, finally, the calibration of the odometer depends upon the environment.

Odometer calibration depends upon the environment

If the environment experienced by the dancing bee en route to the feeder in experiments 2 and 4 is different, then it generates a different relationship between waggle run duration and distance.

For example, if one feeder was across a closely mown lawn and the other was across dense shrubby woodland, they would each generate a unique optic flow, so changing the image motion experienced, and hence the waggle run generated.

In the diagram above, you shouldn’t use dance calibration for bees trained to direction A to determine the distance bees going in direction B would forage.

Phew!

Optic flow, waggle dancing and implications for practical beekeeping

None 😉

At least, none that I can think of.

A Caterham 7 isn’t an ideal car for a beekeeper but would be a lot of fun to help you understand optic flow 😉

Most of us keep our bees in mixed environments. Your apiary isn’t situated with a cliff edge on one side and an unbroken prairie on the other. Since the environment is mixed, the waggle dance calibration is not going to be wildly different, whichever way the bees fly off in. You can therefore use an approximate figure of 1 second per kilometre to estimate the the distance at which your bees are foraging, irrespective of the direction they go.


Notes

Most of the referenced studies are at least two decades old. Honey bees have remained a fertile research tool for neurobiologists. Our understanding of honey bee vision continues to improve. However, I cannot discuss any of these more recent studies with reference to optic flow. Anyway, just because they’re old doesn’t make the experiments any less elegant or interesting 🙂

 

The waggle dance

Ask a non-beekeeper what they know about bees and you’ll probably get answers that involve honey or stings.

Press them a little bit more about what they know about other than honey and stings and some will mention the ‘waggle dance’. 

Karl von Frisch

That the waggle dance is such a well-known feature of honey bee biology is probably explained by two (related) things; it involves a relatively complex form of communication in a non-human animal, and because Karl von Frisch – the scientist who decoded the waggle dance – received the Nobel Prize 1 for his studies in 1973.

Von Frisch did not discover the waggle dance. Nicholas Unhoch described the dance at least a century before Von Frisch decoded the movement, and Ernst Spitzner – 35 years earlier still – observed dancing bees and suggested they were communicating odours of food resources available in the environment.

Inevitably, Aristotle also made a contribution. He described flower constancy 2 and suggested that foragers could communicate this to other bees.

Language and communication are important. The development of language in early humans almost certainly contributed to the evolution of our culture, society and technology. Communication in non-human animals, from the chirping of grasshoppers to the singing of whales, is of interest to scientists and non-scientists alike.

It is therefore unsurprising that the ‘dance language’ of honey bees is also of great interest. Although not a ‘language’ in the true sense of the word, Von Frisch described the symbolic language of bees as “the most astounding example of non-primate communication that we know” over 50 years ago. This still applies.

The waggle dance

The waggle dance usually takes place in the dark on the vertical face of a comb in the brood nest, usually close to the nest entrance. The dance is performed by a successful forager i.e. one that has located a good source of pollen, nectar or water, and provides information on the presence, the quality, identity, direction and distance of the source, so enabling nest-mates to find and exploit it.

The dance consists of two phases:

  1. The figure of eight-shaped ‘return phase’ in which the bee circles back, alternately clockwise and anticlockwise, to the start of …
  2. The ‘waggle phase’, which is a short linear run in which the dancer vigorously waggles her abdomen from side to side.

The direction of the food source is indicated by the angle of the waggle phase from gravity i.e. a vertical line down the face of the comb. This angle (α in the figure below) indicates the bearing from the direction of the sun that needs to be followed to reach the food source. 

For example, if the dancer performs a waggle phase vertically down the face of the comb, the food source must be opposite the current position of the sun.

The waggle dance

The distance information is conveyed by the duration of the waggle phase. The longer this run is, the more distant the source. A run of 1 second duration indicates the food source is about 1 kilometre away.

The quality of the food source is indicated by the vigour of the waggling during the waggle phase and the speed with which the return phase is conducted. 

Surely it can’t be that simple?

Yes, it can.

What I’ve described above allows you to interpret the waggle dance sufficiently well to know where your bees are foraging.

Next time you lift a frame from a hive and see a dancing bee, circling around in a little cleared ‘dance floor’ surrounded by a group of attentive workers, try and decode the dance.

Remember that the dance is performed with relation to gravity in the darkened hive. You’re looking to identify the angle from a vertical line up the face of the brood comb to determine the direction from the sun.

Time a few waggle phases (one elephant, two elephants etc.) and you’ll know how far away the food source is.

Really, it’s that simple?

Of course not 😉

The waggle dance was decoded more than half a century ago and remains an active subject for researchers interested in animal communication.

What you’ll miss in your observations is an indication of the type of nectar or pollen resource that the dancing bee is communicating. The dancing worker carries the odour of the food source and may also regurgitate nectar, presumably helping those ‘watching’ (remember, it’s dark … nothing to see here!) determine the type of resource to look for when they leave the hive.

You will also be unable to detect the pulsed thoracic vibrations that the dancing bee produces. These are also indicators of the quality of the food source; better (e.g. higher sucrose content) resources elicit increased pulse duration, velocity amplitude and duty cycle, though the number of pulses is related to the duration of the waggle phase, and so is another potential indicator of distance.

Inevitably, there are also pheromones involved.

There always are 😉

The dancing bee produces two alkanes, tricosane and pentacosane, and two alkenes, Z-(9)-tricosene and Z-(9)-pentacosene. These appear to stimulate foraging activity 3.

But it’s cloudy … or rain stops play … or nighttime

What happens to dancing bees if foraging is interrupted, for example by poor weather or night? 

The dancing bee continues to change the angle of the waggle phase as the sun moves across the sky. This means that a dancing bee will correctly signal the direction to the food source, even if they have not left the hive for several hours.

During their initial orientation flights they learn the sun’s azimuth as a function of the time of day, and use this to compensate for the sun’s time-dependent movement.

Some bees even dance during the night, in which case the watching workers must presumably make their own compensations for the time that has elapsed since the dance 4.

And what happens if the sun is obscured … by clouds, or buildings or dense woodland? How can those directions be followed?

Under these circumstances the foraging bee detects the position of the sun by the pattern of polarised light in the sky. 

Scout bees

The waggle dance is also performed by scout bees on the surface of a bivouacked swarm. In this instance it is used to communicate the quality, direction and distance of a new potential nest site. 

Swarm of bees

Swarm of bees

The intended audience in this instance are other scout bees, rather than the general forager population 5. These scouts use a quorum decision making process to determine the ‘best’ nest site in the area to which the bivouacked swarm eventually relocates.

The shape of the bivouac often lacks a true vertical surface. However, since it’s in the open the dancing bees can orientate the waggle run directly with relation to the sun’s direction, rather than to gravity.

Under experimental conditions the dancing bee can communicate the presence and quality of a food source on a horizontal comb, but – with no reference to gravity – all directional information is lost 6.

The round dance

The duration of the waggle phase is related to the distance from the nest to the food source. Therefore the recognisable waggle dance tends to get difficult to interpret for sources very close to the nest.

It used to be thought that there was a distinct directionless dance (the ’round dance’) for these nearby i.e. 10-40 metres, food sources. However, more recent study 7 suggests that dancers were able to convey both distance and direction information irrespective of the separation of nest and food source. This indicates that bees have just one type of dance for forager recruitment, the waggle dance.

Do all bees communicate using a waggle dance?

There are a very large number of bee species. In the UK alone there are 270 species, 250 of which are solitary.

There’s a clue.

Solitary bees are like me at a disco … they have no one to dance with 🙁

I’ll cut to the chase to help you erase that vision.

The only bees that use the waggle dance are honey bees. These all belong to the genus Apis.

They include our honey bee, the western honey bee (Apis mellifera), together with a further seven species:

  1. Black dwarf honey bee (Apis andreniformis)
  2. Red dwarf honey bee (Apis florea)
  3. Giant honey bee (Apis dorsata)
  4. Himalayan giant honey bee (Apis laboriosa
  5. Eastern honey bee (Apis cerana)
  6. Koschevnikov’s honey bee (Apis koschevnikovi)
  7. Philippine honey bee (Apis nigrocincta)

Dancing and evolution

Dwarf honey bees nest in the open on a branch and dance on the horizontal surface of the nest. The waggle run is orientated ‘towards’ the food source. Apis dorsata is also an open-nesting bee, but forms large vertically-hanging combs. It dances relative to gravity, and indicates the direction by the angle of the waggle run in the same way that A. mellifera does.

The cavity nesting bees, A. cerana, A. mellifera, A. koschevnikovi, and A. nigrocinta produce the most developed form of the dance.

The dances of A. mellifera and A. cerana are sufficiently similar that they can follow and decode the dance of the other.

The complexity of the nest site and the waggle dance reflects the evolution of these bee species. The earliest to evolve (i.e. the most primitive), A. andreniformis and florea, have the simplest nests and the most basic waggle dance. In contrast, the cavity nesting species evolved most recently, form the most complex brood nests and have the most derived waggle dance.

When and why did the waggle dance evolve?

Assuming that the waggle dance did not independently evolve (there’s no evidence it did, and ample evidence due to its similarity between species that it evolved only once) it must have first appeared at least 20 million years ago, when extant honey bee species diverged during the early Miocene.

The ‘why’ it evolved is a bit more difficult to address.

Behavioural changes often arise in response to the environment in which a species evolves.

Bipedalism in non-human primates (like the australopithecines) is hypothesised to have evolved in part due to a reduction in forest cover and the increase in savannah. Apes had to walk further between clumps of trees and bipedalism offered greater travel efficiency.

Perhaps the waggle dance evolved to exploit a particular type or distribution of food reserves?

In this regard it is interesting that the ‘benefit’ of waggle dance communication varies through the season.

If you turn a hive on its side the combs are horizontal 8. Under these conditions the dancing bees can communicate the presence and quality of a food source. However, they cannot communicate its location (either direction or distance).

No directional or distance information is now available

In landmark studies Sherman and Visscher 9 showed that, at certain periods during the season, the absence of this positional information did not affect the weight gain by the hive i.e. the foraging efficiency of the colony.

They concluded that during these periods forage must be sufficiently abundant that simply stimulating foraging was sufficient. Remember those alkanes and alkenes produced by dancing bees that do exactly that?

Tropical habitats

This observation, and some elegant experimental and modelling studies, suggest that dancing is beneficial when food resources are: 

  • sparsely distributed – therefore difficult (and energetically unfavourable) to find by individual scouting
  • clustered or short-lived resources – when it’s gone, it’s gone
  • distributed with high species richness – if there’s a huge range of flowers, which are the most energetically rewarding (sugar-rich) to collect nectar from?

One of the experimental studies that contributed to these conclusions (though there’s still controversy in this area) was the demonstration that waggle dancing was beneficial in a tropical habitat, but not in two temperate habitats. This makes sense, as food resources have different spatiotemporal distribution in these habitats. Tropical habitats are characterised by clustered and short-lived resources.

Therefore the suggestion is that the waggle dance of Apis species evolved, presumable early in the speciation of the genus, in a tropical region where food resources were patchily distributed, available for only limited period and present alongside a wide variety of other (less good) choices.

For example, like individual trees flowering in a forest …

Finally, it’s worth noting that there is evidence that bees that dance are able to successfully exploit food resources further away than would otherwise be expected from their body size.

This also makes sense.

It’s much less risky flying off over the horizon if you know there’s something to collect once you get there 10.


Notes

If you arrived here from my Twitter feed (@The_Apiarist) you’ll have seen the tweet started with the words “Dance like nobody’s watching”, words that are often attributed to Mark Twain. 

The full quote is something like “Dance like nobody’s watching; love like you’ve never been hurt. Sing like nobody’s listening; live like it’s heaven on earth”.

Pretty sound advice.

But it’s not by Mark Twain. It’s actually from a country music song by Susanna Clark and Richard Leigh. This was first released on the Don Williams album Traces in 1987. So only about 90 years out 😉