Summary of Bumblebee (Bombus Terrestris) Observations & Behaviour
This page is devoted to a summary of the empirical observations we've made during our study of bumblebee colonies.
2020 update: we have now (finally!) completed our analysis of what triggers bumblebees to start foraging each day. You can read the full page here.
Our colonies are "pseudo-wild", in the sense that they are not kept in a lab, rather their nest is outdoors and they are free to forage completely naturally in the wild environment and subject to the whims of the weather. However, by the same token, most of the observation has come from commercially sourced colonies, living in a man-made nest container, with some intrusion (such as infra red cameras), and a nest location chosen by us, not them. Clearly there is potential for some of these factors to affect their behaviour.
If you're looking to discover the amazing world of bumblebees then by all means please use this page as a starting point and feel free to get in touch with any questions. Conversely, if you have or know of research that augments what we have here, please also get in touch. (It remains an outstanding task to reference some of the 3rd party research in these areas).
The observations here are essentially adhoc and based on a small number of colonies (though we intimately share in their life by way of internet-enabled CCTV!) so while extensive in terms of "man hours" cannot be said to be truly scientific, except where noted. So, if you can add to the science, please do!
On this page
This page is long, so to help understanding what it covers, here's an at-a-glance view:
Audio Communication
Audio Frequencies
Bedding
Captivity
Caring for Sick & Dead
Door Duty
Dual / Triple Colonies
Early Queens
Ejection of intruders & foreign bodies
Fanning
Fighting
First Flight Flap Navigation
Flight Times
Flying Speed
Leaving to Die
Lifespan
Mating
Memorisation (Orientation) & Launch
Moss Burrowing
Navigation
[Nest Robbing - NEW - data coming soon]
Overnight Stop Outs / Early Leavers
Pollen Turnaround Times
Stink Bombs
[Stockpiling - NEW - data coming soon]
Temperature / Weather Sampling
Training (e.g. to accept intrusion)
Warning Levels
Working Day
Audio Communication
We are currently making recordings of audio patterns in the nest that do not conform to regular buzzing - such as repetitive "chirps" by a single bee while the rest of the colony remains silent. Our question: is this some form of communication?
Since we also have a disabled queen indoors we are also monitoring various "squawks" she makes, as warnings and also when feeding.
Details will follow in due course.
Audio Frequencies
Starting 2012 we've been sampling audio frequencies under various conditions, results include:
Buzzing in the nest - 190 ±5 Hz
Queen normal buzzing (thorax) - ~130 Hz
Fanning - 130 - 150 Hz
Possible Hatching? - 180 Hz
Short Warning "Squawk" from Queen - 185Hz
Alarm response - 400 - 500Hz
Bedding
What can I say? Just sit back and marvel at this solitary bumblebee (2011B1 2nd Colony) arranging bedding in the nest over the course of 7 hours through the night.
She's not daft, she's moved it right under the heat of the infrared camera. Go Girl!
Captivity
This section has to be completed.
We have cared for numerous unable-to-fly bumblebees indoors in an articificial environment and observed many behaviours and apparent adapations, interactions with each other, "moods" and more:
'Depression' in bumblebees? We probably think so.
Nursing: one bumblebee quite clearly nudged and righted its 5 legged sister when she was stuck on her back
Becoming used to human intrusion: definitely
Anticipating the arrival of food: yes
Showing instincts for camouflage & protective measures: yes
Free to choose light or dark, inside or out - which will it be? Does it depend on the others?: seems so
Caring for Sick & Dead
In box 2011K1 it turned out that our camera was very nearly over the point where the bumblebees mainly collected to die - this was in the front corner of the box. It was also near the pollen supply inside the box.
On several occasions we observed bees dragging dead or struggling siblings to this area. In one case it appeared as though the bumblebee tried to revive a struggling bumblebee by taking it to the pollen area (not that it would necessarily do any good). This is probably an over-rationalisation on our part; suffice to say, the struggling bumblebee was dragged to one part of the nest and "fussed over", then later when/as it died, it was moved back. In fact, we have video of bumblebees arranging their dead:
How did that first bee come to bee there? This video shows how - what is intriguing is the time spent by the worker "tending" to the body, given how easily it drags it to the final resting location and leaves, why does it spend a few minutes "fussing" over the dead bee?
Door Duty
The multi-role existence of bumblebees is well documented. One (some) of these roles certainly concern security of the nest. During the night, particularly, we see "perimeter patrols" - a bumblebee that traces a repeated route round the edge of nest (in the beepol lodge, this is typically the join of the base & lid - where cool air & light can be sensed).
Furthermore, on cool/wet days it is common to see a bumblebee standing guard in the entrance, looking out of the nest. Their role appears to be monitoring outdoor conditions and acting as a barrier to other bumblebees leaving the nest. We've seen a very modest size bee force huge queens to turn round and go back into the nest.
In particular in box 2012B1, due to revised camera setup, we can clearly see activity in the entrance hole. In fact there is a guard bee(s) on permanent 24x7 duty. The guard bee is facing out of the nest and blocking the passageway. When a bee returns from outside, the guard bee moves over a little and they pass side to side (occasionally over the top of each other if there is a sudden rush on!) When a bumblebee approaches from inside she does not move, and occasionally lifts her wings slightly to increase her blockage. At this point the exiting bee has one of two choices: turn round back into the nest (about 90% do) or push on to get past.
In the case of the latter, the bumblebee has to shove its way forward and past. The guard bee allows it to do this and there appears to be no aggression, but there is a certain "jostling for position".
Here's one girl who's been on duty for over 8 hours:
standing guard at the entrance - keeping an eye on the weather and stopping foolish exits
Nest Security
When the nest is disturbed, "security" bumblebees will come to investigate. For a minor disturbance one will emerge and check the entrance and if necessary also do a check of the exterior of the nest (e.g. climb over the roof and sides of the lodge). After this check, typically they will remain in the entrance for up to 45 minutes (as per picture above).
For a more severe disturbance (such as roof loss) more will coming running (flying if day time) and potentially attack the source of threat. As the threat subsides they will take up a "watchtower" position and again, for about 45 minutes, stand guard and protect the perimeter of the nest.
For example, this occured when we attempted to remove the plastic lid from our beepol nest 2012B1. About a dozen bumblebees came to defence and (since the lodge lid was lifted) out onto the lodge. As the situation calmed, most returned, but 4 stood guard at regular spacings along the ledge of the lodge base (thus we couldn't fully shut the lodge without crushing them). After half an hour, all but one had returned to the nest. After another 20 minutes all had returned and we could close the lodge lid.
Dual / Triple Colonies
Dual Colonies are reported for some species although the literature I've read suggests they are fairly rare.
A dual colony occurs when a second colony cycle begins in the nest in direct succession after the first colony, before the onset of hibernation/winter. Conventionally the bumblebee nest is expected to have a single colony that descends into a somehat chaotic "competitive" phase at the end of its natural life; at this time the "Mother" queen produces offspring queens and males. These leave the nest, and theoretically do not return, instead going to mate and then death for the boys and hibernation for the queens.
This was not the pattern for our 2011B1 colony which we actually acquired in August (i.e late in the season). At this time it was under-developed, barely surviving, had suffered heat damage and a few days later the queen emerged to die.
Typically that would be the end of the colony with its remaining residents (workers) dying, queens and boys leaving to mate. We counted about 7 off-spring queens which for a short time continued to use the nest harmoniously (indeed, we observed one mating with another species whilst flying into the nest). These queens began to leave but one stayed, began collecting pollen, and a second colony developed. This produced very small bees and was not particularly successful, with the queen dying inside the box after 7 weeks.
We really did think is was all over at this stage, until a few days later another Queen arrived at the box from outside and eventually took up residence; over the coming days she was joined by two others and they appeared to reside harmoniously and started collecting pollen. A further colony continued to develop during the 4 weeks these queens were alive, though most of the offspring were underformed (e.g. 7mm) and unable to survive. The final queen died 16th November, with the final worker emerging 24th November, and dying in our care 30th November.
[Here's a tiny under-formed worker from the second colony]
I've also been in touch with the folks at dragonfli who supplied the colony, and they too had a triple colony in 2011.
Early Queens
Our 2012B1 colony is already showing a departure from the norm, with a minimum of 5 early queens being produced already by 16th April and I believe more since. These queens have performed memorisation and have been on foraging trips and to my knowledge all have returned so far. One or two of these queens have also started returning with pollen.
At the time of writing we are currently tracking their progress and behaviour.
Early queen memorising - showing dramatic size differenceunmistakably a queen bee at the entrance, with a regular sized worker. The sizing grid is spaced at 1cm intervals.
For the first 5 active days of 2012B1 Colony (photos above) we have tracked trips and memorisation/orientation flights (16th - 20th April) to get an impression of the size of the colony. The Data is as follows:
Total Trips: 925
Queen Trips (included in above): 62
Memorisation Flights: 228
Queen Memorisation Flights: 21
Although some memorisation flights are no doubt re-enforcement attempts, it's hard to believe there are so many Queens in the nest, so early. But the image below (taken 29th April) during a long period of rain and cold shows just how the Queens in the nest are queuing up (8 in this image).
Queens stacked up near the entrance on cold/rainy day - there is warmth from the infra-red camera here
Ejection of intruders & foreign bodies
Bumblebees will protect their colony from intrusion where possible and forcibly eject or carry out unwanted guests and items in the nest. (Wax moth is a particular threat and is so overpowering, they struggle to deal with it)
Here's viedo of a bee carrying away a foreign larvae from the nest:
What makes this more remarkable is this was her first flight! She had to perform memorisation before being able to fly off. Her trip was 2 minutes, and we estimate that the larvae was deposited at a distance of up to half a kilometre.
And here's a video of a bumblebee removing something "egg like".
Fanning
Fanning is a wing-flapping technique bumblebees use to cool their nest and improve airflow (e.g. to reduce CO2). It's intended to keep the nest at the optimum temperature (30C at the core).
Our observations show that different bees have different thresholds for fanning. In our 2012B1 colony, for example, one bumblebee moves to the entrance and starts fanning when the ambient temperature in the lodge reaches about 21.5C (even if it is wet), even though arguably this is far earlier than necessary to prevent the nest from exceeding 30C. My theory is that natural variation in the trigger point of individual bumblebees is actually a great mechanism for controlling nest temperature and balancing the need to fan and need to work.
Indeed, research shows this to be the case and not only do trigger points vary, but probabilty of response by a given bumblebee is not 100% (this causes the work to be shared); and duration of fanning varies (again causing the work to be shared). It's an elegant and advantageous behavioural design.
[The paper is entitled: The control of nest climate in bumblebee (Bombus terrestris) colonies: interindividual variability and self reinforcement in fanning response by Anja Weidenmuller]
Very clear fanning behaviour at nest entrance
Measured audio frequencies of fanning currently show 130Hz - 150Hz for normal workers
In box 2012B1 we have seen a Queen fanning at 22.3C - frequency 119Hz
A bufftailed Queen fanning at the nest entrance - 22.3C - 119Hz
Fighting
Bumblebees are known to fight in order to protect the nest. And queens will also fight to gain dominance of a nest/nest site.
Here we see a worker bee (Bufftailed/Bombus Terrestris or Whitetailed/Bombus Lucorum) attacking and fighting a cuckoo bee (Bombus Vestalis) presumably after having ejected it from the nest.
First-flight Flap navigation
Our Beepol lodge is now equipped with an anti-wax moth plastic flap, which the bees have to learn to open. (It is beyond the strength and wit of a wax moth). In general the bumblebees can learn to operate this flap successfully, however, we've made the following oberservations:
1) Not all bumblebees seem to identify the flap as the entrance upon their return. A number of them explore the lodge where scent is strongest (along joins), often scratching at these locations attempting to enter. Some remain outside the lodge for several hours, usually until by chance they discover the flap. In some cases they walk right underneath the flap, even turn such they could climb directly into the nest (i.e. between the entrance mouth and flap) and yet still do not enter! (As an observer, this is baffling!) We are wondering whether reflections of the sky in the flap (due to angle) are disguising the dark entrance. We are going to experiment with this.
scooping under the flap to return (image CH1)
2) The first exit via the flap is troublesome for the majority of the bumblebees. As they push on it horizonally it moves up, such that they can step down and crawl underneath it. However, this does not seem to be natural to them. Even though they could easily scoop down underneath it, they continue to push horizontally against the flap, struggling to push it wider as it resists more & slips against them. It could well be the instinct is to try and push the obstruction completely out of the way of the nest, as if, say it was a leaf. Eventually, possibly even out of tiredness, they dip down and this gives them a very simple and clear exit. This behaviour is a guarantee this is the bumblebee's first exit from the nest, and without fail it performs full memorisation.
Once the bumblebees have learnt to use the flap, they do so with ease, hunkering down naturally on their return, and sliding out easily by dipping down on exit. They would have to do this in nature if, say, a leaf was covering the entrance.
Flight Times
{to be completed - data exists}
For un-numbered bees we rely on visual identification to monitor trip/flight times. Consequently we've been able to collect the following data:
1st Colony flight of the day (regardless of bumblebee)
Round Trip time Mean 12 min 13 seconds - STDEV 10:48
The STDEV is possibly a misnomer, and we hope to re-analyse the data, as the trips tend to cluster around 2 mins (pretty much a weather check or local nectar top-up), 15 mins and 25mins, the longer trips usually returning pollen.
We also have data for our 2011B1 2nd colony on all trip times combined (small number of indentifiable workers) and also trip times for a specific queen collecting pollen. THe full data is to be analysed, suffice to say that mean trip times for the queen were around 70 mins and tightly regulated, so much so, we were often able to predict when she would return.
Flying Speed
it's pretty hard to judge the speed of bumblebees over distance because not only is it rather fast, but they very quickly become difficult to see! We're fortunate, however, that our camera set-up gives us a view of the bumbles taking off and landing, and every once in a while the alignment of the bees, the moon, planets and stars allows us to get enough frames to calculate a speed. ☺
It's quite remarkable that some of the bees look like they are on elastic when they take off - they absolutely shoot off the ledge appearing on only one frame of footage - the acceleration must be quite large, I'd love to figure out how many "G"'s it is. Unlike conventional wings, which require airflow to create lift (which is why the whole myth about "bumblebees shouldn't be able to fly" grew up), bumble wing design doesn't. Consequently the wings themselves can power the take off, rather than (say) having to dive into a fall (like a bird).
Our fastest bee to date was calculated at 42mph - this was from our frame rate of 12.5 frames per second across a known distance of 10 metres (about 6 frames)
Leaving to Die
Many bumblebees will leave the nest to die during their last remaining hours or days. Sometimes this is within a very short time - a few hours - and they are clearly unwell or tired/old and becoming immobile. In other cases, the bumblebees often appear suitably mobile and healthy, though often very faded. These bees will typically spend a number of days in the vicinity of the nest, but outside (e.g. sheltering on a ledge on the lodge). After a few days they are seen to leave this area and not return, despite (for example) the availability of good immediately available. However, they do not seem to go far and are often found dead within the immediate few feet of the nest. It may well be that cold, wet and lack of food finally contributes to their demise in these circumstances.
Clearly there is an evolutionary advantage (for the remainder of the colony) to this behaviour.
Lifespan
Holly was the first Bufftailed worker that we rescued (2011). She was disabled: missing a wing, a leg and with a crooked/deformed body, about 10mm. Typically her lifespan would not be estimated at more than about 14 days. (It would have been decidely less if left outdoors, as she could not fly and thus feed, and kept leaving the nest).
Holly lived 70 days in our care. She was a very old lady! But her record has now been broken - Dusty (2012 Beepol Colony) lived till 102 days in our care. (She may well have been a few days old when we found her).
In contrast:
BLB (medium worker) - 10 days
Lucy (tiny worker) - 16 days
LBB (male) - 8 days
Bea (tiny worker from 2nd colony (October)) - 17 days
Tiny worker from 3rd colony (November) - 6 days
Poppy (tiny worker from 3rd colony (November)) - 6 days
Holly (tiny worker from koppert colony 2011) - 70 days
Dusty (tiny worker, beepol colony 2012) - 102 days
This video is Dusty in her old age - 99 days - she is very shaky and has a loss of co-ordination that was quite noticeable. On day 99 when we saw this we (correctly) felt she would die soon.
Mating
In colony 2011B1 we observed one instance of a 2nd Generation Queen (i.e. daughter of the colony "mother" queen) mating as she flew into the nest. What's more remarkable, is our Bufftailed queen was mating with a Redtailed boy!
This boy entered the nest with the queen and remained in there for 20 minutes. After this episode he performed a memorisation flight on leaving and returned regularly into the nest over the next few days.
Memorisation (Orientation) & Launch
Memorisation of the nest entrance and its location upon first flight is a well-documented behaviour. The recognised term is actually "Orientation Flight" but I dislike this term for being misleading, as orientation can occur even when the bumblebee is not planning on returning (i.e. making a mental map), such as when a captured queen is released from a new location, and it is a different type of flight pattern.
During "Memorisation" The bumblebee typically launches backwards and flies in arc-swings to and fro, memorising the appearance of the nest. The arcs get wider and higher, sometimes resulting in circles over a 10 metre area. After about 30 - 120 seconds, memorisation is complete and the bumblebee leaves to forage.
Occasionally the bumblebee returns quickly after starting this procedure, e.g. within 5 - 20 seconds, particularly if the weather is inclement, or in some cases it seems, just if they are unsteady. First flights seem to fall into one of two camps - a "finding your wings" kind of flight, in the region of 10 minutes, which usually results in the bumblebee returning to the nest without having collected pollen; or a full foraging trip of at least 25 minutes, with pollen being returned.
Some bumblebees, again usually the smallest and least confident, line up to perform memorisation, make a few unsteady flaps, and then decide to return to the nest without taking off. Flying is not for them!
Seeing memorisation is one of my most joyful moments of keeping Bumblebees, it indicates new life emerging into the wide world for the first time; here's a short montage..
Memorisation is not necessarily a one-time affair. We estimate around 10% of the bumblebees perform a partial "re-memorisation" on future trips. This process is much less intense. The initial arcs are not usually as close to the nest entrance and the whole affair usually only lasts 1/3rd of the time; indeed, the primary aim seems to be re-memorisation of the immediate nest front. We speculate this may be a built-in instinct to deal with nest features that change in nature (e.g. where plants grow around them). There is nothing apparent that we've observed triggers this behaviour (our nest front is reasonably static, save for when we are standing by it) - it appears to occur at the bumblebee's own whim.
We have also noted that a small numbers of bumblebees launch into flight backwards, typically when they intend to fly up and over the nest site - which thus saves them an in flight turn. Not all bumblebees do this, however, as our 2011B1 nest was sited facing away from the prevailing garden exit, and only some bees chose to launch backwards without needing to turn. They are the smart ones who used slightly less energy to get out of the garden.
Moss Burrowing
We've often seen Queens nest searching along mossy banks and it is known that bumblebees like to find mossy areas for nesting. Indeed the Carder bee actually uses it in its nest as lining/insulation. (Carding, means "combing".)
This video shows both a redtail queen and a bufftail queen burrowing in moss. The behaviour, to me, is not fully explicable, as it seem patently obvious there is no cavity worthy of nesting or searching. And indeed, usually when nest searching queens are very quick to evaluate suitability of the location, usually on the wing. So, quite what attracts these queens to spend several minutes poring over the same but of moss is not clear. We can't be sure if these queens are what we call "mother queens" (i.e. out of hibernation, looking to set up their first nest), or newly emerged "daughter" queens from a successful colony, prior to mating. (The reason for the uncertainty is it was recorded 25th May, after a hot March, and terribly wet April, which seems to have thrown some of the natural cycles out of kilter.)
Navigation
Despite incredible navigation skills, not everything always goes to plan in bumbleworld. This one swooped in towards the nest entrance at a great rate of knots and slightly (and rather bafflingly) missed the entrance hole. Forgot the sunglasses perhaps?
We estimate incoming speed at about 17.5 metres per second from the video frame rate (about 39 miles per hour) - clearly ignoring the 30mph limit signs!
Overnight Stop Outs / Early Leavers
In both 2011K1 and 2011B1 colonies we witnessed a small number of bees that stayed away from the nest every night. In the case of 2011K1 we could not identify if it was the same bumblebee each time, as they were not uniquely identifiable. However, in 2011B1, due to the smaller number in the colony, we could actually identify the bees visually from their size and markings (and, as we discovered, behaviour).
They typical pattern was to leave nest around 20 minutes after the last bumblebee had returned and return the following morning at around sunrise, or just before, beating the first leavers from the nest. In both colonies this behaviour was shown by only one bumblebee (i.e. only one left each night) and in the case of 2011B1 we can say it was the same bee each time.
We are at a loss to explain this behaviour - as it seems a highly risky strategy for the individual for no apparent gain, and goes against the general "risk management" strategies that are in place in the colony.
One possibility is this mechanism is in part responsible for governing the "first leaver" behaviour - see Temperature/Weather Sampling and Working Day below. Does the return of an overnight "stay out" trigger the start of the day for the colony? (We need to re-examine existing data & gather more).
We were also baffled when towards the end of her life, the 3rd Generation Queen (2011B1) began coming out of the nest at around 4am in the morning. She did this repeatedly for a number of days. This was during November, so cannot be explained by either warm temperatures or sunrise. This seems to go beyond the normal security instinct, in which bees remain in the entrance. Is it possible that cold winter temperatures trigger the same response as (say) loss of nest roof? (sudden loss of heat)
We have video below - the quality is poor because of the infrared brightness from two cameras, but she is discernible.
Ultimately it seems she wanted to die outside the nest. On her final early morning exit she disappeared from view and we could not find her. Miraculously she returned to the entrance 4 days later in a very poor state of health. Attempts to revive her only succeeded in keeping her alive for a few hours and she died later in our care.
Pollen Turnaround Time
During the second colony of 2011B1 (September 2011) we were able the track each and every foraging trip of one of the workers in the colony, due to low numbers of works in the nest and unique features. Data for foraging trip times and "pollen turnaround" time (time taken to deposit pollen in the nest before leaving again) was as follows over a sample of 44 consecutive trips:
Average Trip Time: 23.56 mins (STDEV 7.35 mins)
Pollen Turnaround: 5.05 mins (STDEV 2.18 mins)
If we consider the flying and foraging time as the effective work by the bumblebee, and the turnaround as overhead (using aircraft as analogy) then we can calculate the effective "utilisation" (or efficiency perhaps) of the bumblebee as a ratio. In this case: 82.35%
Stink Bombs
2012 was the first year we kept a damaged Queen indoors. Aside from her fasincating behaviour to control "her" workers (they were sisters, not daughters) one particular activity that took us by surprise was her ability to create "Stink Bombs". She does this is the nest is threatened. Her behaviour under threat is a little different to workers (probably for evolutionary reasons).
She will buzz her wings for a short while, possibly repeatedly
She will let off a foul and extremely powerful vomit-like smell which very rapidly fills the nest space and indeed room. It clears usually within about 2 minutes.
She will then go for cover and avoid the danger - presumably allowing her workers to defend her
it is not clear if the "stink bomb" is a signal to her workers, a signal to the threat, or both.
Temperature / Weather Sampling
How do bumblebees know when to leave the nest and know what the outside conditions are? Especially given the reliability with which they are able to leave the nest first thing. Good question.
We've observed the following and think it contributes to monitoring the weather:
A solitary bee standing guard in the entrance for extended periods of time (many hours, even overnight) - often acting as a barrier for other bumblebees to exit and causing them to turn round. This is particularly prevalent on cold/damp days - as if they are protecting the colony for going out in un-safe conditions.
Periodic sampling during the day - going to the entrance, checking outside withouth actually leaving, turning round. (I suppose this is an obvious strategy).
"Bottom" sampling - very funny to watch, but there seems to be no other sensible explanation for this - when it's dark some bumblebees come to the entrance periodically and stick their tail outside, then return to the nest. Whether this is the most sensitive part of their body, or whether it's purely for safety since they can't see any potential predators, we don't know, but it seems this could be one way they are checking the weather.
Training (e.g. to accept intrusion)
Like Pavlov's dogs, bumblebees can be trained through reward and certainly to recognise where their reward is going to come from (an essential skill in nature).
We observed this incidentally with all the bumeblees we kept indoors and had to feed, in particular Holly, our very first "rescuee". Our feeding technique involved removing the lid of her nest area and reaching with a syringe to fill a small container.
As anticipated at first she reacted strongly to this often with level 4 warnings; however, day by day her warning levels subsided. We ignored her warnings because to respond to them would only re-inforce the "belief" that they worked (even though usually we would back off from a warning to avoid stress to the bumblebee). The bottom line is, Holly needed feeding, so we had to proceed.
Eventually Holly became calm about us removing the lid and poking a syringe into the nest and did not react as if it was a threat. Then a remarkable thing started to happen - she began to associate it with the reward and would thus (intially) come to the honey water shortly after we had added it; she was learning to associate our actions with the honey water (reward). It didn't stop there - after several weeks, she was actually anticipating the reward. When we opened the lid and introduced the syringe, she would come to the container looking for the honey water. There were times when we were trying to add drops to the container and Holly was already there in the way trying to get some!
So, in a sense, you could argue we had "trained" her to accept us coming into the nest and invading her space - correspondingly we never saw any aggression or defence from her subsequently.
This pattern applied to our other bees as well, although none actually got to the point of anticipating and going to the honey container first - basically they didn't live long enough. But over the course of about a week they got to the point where they did not treat our intrusion as a threat.
Warning Levels
We identified four clear levels of warning when bumeblebees are subject to attack or stress, we numbered them as follows:
Warning leg - a front leg is lifted, usually to about 135 degrees, leading to
High Leg - If the threat increases, the leg may be lifted to 160 - 180 degrees - i.e. as far as possible, with the bee turning sideways slightly and almost visibly straining to get the leg as high as possible
Standing up - the bumblebee "stands" like a dog on hind legs, making itself look as large as possible
Presenting the sting - the stand continues, resting on its tail, now with sting brought facing toward the threat. The back legs are spread as wide as possible to make her look as large as possible and the mandibles opened
Ready to sting - in the final level, the bumblebee throws itself onto its back quickly and points its sting at the threat. The legs are pressed down to thrust the abdomen and sting high. It may immediately thrown itself into this position if the threat is particularly significant. If the threat increases, even if there is no contact, it may still eject its venom from a distance
"level 2" warning, Standing up to look largelevel 3 warning - sting primed towards threat, mandibles openlevel 4 warning - sting directed up towards threat
Working Day
Ok, so here comes the science bit - you have been warned. Working days is one area where we scientifically collected and cross referenced a lot of data and I'm currently writing up the results in a more academic format. [The full paper is now actually here]
We looked at the working day of the colony from first bumblebee leaving, to last one returning, to find out what governed it. Sunrise and Sunset were likely candidates so we tracked against sunrise & sunset time, as well as other factors such as weather and temperature.
It will come as no surprise that wet and windy days really throw things out, as the bumblebees will generally not forage. (However, they will fly in some wind - in fact up to 10mph from our observations). So, we looked in more detail at the dry days.
One thing was immediately clear - the last bumblebee comes back to the nest around sunset. There is some variation in this (we have calculated standard deviation), but it seems that the bees will stay out as long as there is enough light to be able to find their way back to nest. Absolute temperature (providing it is in an acceptable range) is not relevant. In this way, the colony safely maximises the working day.
However, first exits tell a different story. There is huge variation in start time, it does not happen at sunrise necessarily, but often 1 or 2 hours later; and absolute temperature again did not reveal a relationship. At first we were at a loss to explain this and find a relationship - light and temperature seemed to be the most logical triggers.
However, when we plotted exit time against the complete temperature chart for the whole night (and not just the value at the time of exit) suddenly the result jumped out: the bumblebees leave when the temperature changes from falling to rising. Depending on cloud and other meteorological factors this does not necessarily occur at sunrise (indeed, the temperature can actually rise all the way through the night at times).
we had limitations in our data as we could only track overnight temperature to the nearest 15 minutes, but almost without fail, the first leaver from the nest did so as the temperature stopped falling and started rising, provided it was already after sunrise. (Exact statistical analysis will be in my paper). Data will be better resolution 2012. But this is why understanding how the bees monitor the temperature outside of the nest so accurately is an intriguing question.
On the best days the bumbles made the maximum possible use of available time - putting in 16 hour working days where possible.
Chart of 2011 working day lengths (normalised from sunrise to sunset) - DRAFT only
