The Queen Bumblebee - Guest Post by Charlotte Rankin

Here in Cornwall, the milder weather has encouraged some brave bumblebee queens to emerge from hibernation and take advantage of the early-flowering plants here. While we do have some winter-active Buff-tail colonies here, most bumblebee queens have been tucked up underground in a long winter’s sleep awaiting Springtime. While in Summer a queen bumblebee proudly secures a nest of up to several hundred individuals, her first few weeks after hibernation are in fact spent solitarily. During this time she ensures a suitable nest site, sets out on foraging expeditions and begins her role as a mother. All whilst battling with Spring’s uncertainties, of course!

A queen Early bumblebee (Bombus pratorum) on Lesser

Celandine, one of the first bumblebee species to emerge

from hibernation. 

As the Spring sun warms the soil, bumblebee queens in their underground burrows start to stir. Here, a queen bumblebee has spent around seven months tucked up in the earth awaiting the Spring alarm. After warming up and with a morning stretch of all six legs, this determined queen eagerly digs her way out of her little burrow, dusts the soil off her coat and sets off into the fresh Spring air to begin the first of her very busy days.

After this long sleep, she is feeling hungry rather than refreshed. She has spent the last several months relying on her energy reserves and her first thought is to find nectar-rich flowers. At this time of year, flowers may be few and far between, but dandelions or a lucky garden find of Mahonia or heather should do the trick. Once revived, a clean of her proboscis and pollen-dusted eyes, she can now begin her next search for a suitable nest site.

Left to right: Red-tailed (Bombus lapidarius), Tree (Bombus hypnorum), Early (Bombus pratorum) and Buff-tailed (Bombus terrestris) queens. Queens here have been found foraging on crocuses, dandelions and lesser celandines. 

She spends considerable time zig-zaging around, searching diligently for a promising site. Depending on her species, she may take a fancy to an old rodent burrow, tussocky grass if she is a Common Carder (Bombus pascuorum), or even an empty bird box if she is a Tree Bumblebee (Bombus hypnorum)!

Following a queen Early Bumblebee (Bombus pratorum), we see her finally decide on an old rodent burrow. While it’s a ramshackle affair of cobwebs and darkness, it provides just what she needs with nesting material conveniently left behind by the previous occupants. She rearranges the material with her little jaws and legs to form a very snug hollow ball, with a single entrance just large enough for her to pass through. In this cavity, she will create a mass of ‘pollen-paste’, made up of pollen and nectar that she has collected on her foraging trips.

Having decided on her home she will set off to explore her new neighbourhood, excitedly flying to and fro and exploring every nook and cranny. She is in fact familiarising herself to its location to ensure that she can return swiftly after her foraging trips. After a few practice flights, she now knows the way to her new home.

During these foraging trips, she battles with the uncertainties of Spring. While the air may be clear and sunny when she leaves, she often returns to her nest with a very soggy, matted coat. Nevertheless, her hind legs are stuffed with pollen and she quickly resumes to the task of constructing her nest. Having mated the previous Autumn, she lays her first batch of eggs upon this ‘pollen-paste’ mass and seals off the structure with wax, which is in fact only around the size of a pea!

Just like birds, she too incubates her brood day and night. This energetically-demanding task requires a lot of nectar. To prevent her from leaving her brood for too long, she cleverly crafts a small wax pot in front of her and fills this with regurgitated nectar. She sips from this while she incubates her brood, replenishing her little pot when necessary.

After a few days, these eggs will hatch into very hungry larvae. As the larvae greedily eat, the queen replenishes this pollen and distributes a mixture of nectar and pollen amongst them. Once fully grown, the larvae will then each tuck themselves up into a cocoon. The cocoons are arranged such that there is a groove that fits perfectly with the queen’s underside. By stretching out her abdomen and hugging all six legs around her cocoons, she ensures their continual warmth for the next few weeks before her brood are ready to bite through their cocoons as adults.

Their movements hesitant and much like a baby’s first steps, the first of her workers are out. Once they have found their feet (all six of them!), they will fulfil their role as baby bee guardians and take over the collection of nectar and pollen to bring back to the nest. However, the queen’s work isn’t over yet – she has a colony of workers to build!

Charlotte Rankin is an ecologist with a passion for bumblebees that embraces both research and conservation. She is a volunteer for the Cornish branch of the Bumblebee Conservation Trust and last year she created two booklets for the conservation group, Penryn Buzz to promote their Bee Ranger project. She has also helped the charity Buglife in establishing their Urban Buzz project in Falmouth. You can follow Charlotte on Twitter at, @bumble_being

Bumblebee count No.2

My timetable and dismal weather during my free time this week prevented me returning to the bumblebee nest until a week after my last count. Not that the weather was inviting as I began walking to the site, the dark clouds suggested rain and the strong wind was cold. Not surprisingly I saw no honeybees, hoverflies or solitary bees about. Bumblebees generally shrug off bad weather, they are tough determined little beasts.

The only other bee seen was this queen Bombus
terrestris (Buff-tailed bumblebee) feeding on
heather near to the nest.

As I approached the nest the first question in my mind was, would it still be active? No one knows with certainty how long these winter colonies last. Within a couple of minutes a bee arrived and entered the nest so I began setting up my tripod and camera to film the nest.

Filming the bees entering or leaving the nest offers a number of advantages. From the perspective of personal comfort it is preferable to watch a video in the warm than stand outside conducting the count. If my comfort is of no concern, it also offers greater accuracy as the video can be replayed and examined frame by frame. Having video also offers the possibility of recounts and the availability of other people to view it.

It had rained earlier in the morning and bumblebees have a tendency not to collect wet pollen. Out of the forty bees that returned to the nest only one carried pollen. It was debatable whether the bee had collected the pollen, it was spread on its hind legs rather than rolled into a ball as usual. It returned in the last few minutes of filming and may indicated that the flower's pollen was drying out and some stuck to the hairs on the bee's leg.

The other notable observation was that one worker exited the nest but rather than flying away, turned round and re-entered the nest - see video.

Compared to last week, there were less bees seen in a similar time span. This may be due to several possible reasons. The colony size may have decreased or possibly the bee's foraging activity may have been less due to the adverse weather, wet pollen or the difference in the time of day between the two observations.

The only certainty gained by comparing both day's counting is that more data is needed. It seems I have a new task for next week's to do list.

Bombus terrestris nest - Falmouth 3rd March 2017 11.14hrs+
P/N? = unable to distinguish whether bee had pollen due to hind legs obscured 

DUR MINS	BEES IN	BEES OUT	POLLEN	NECTAR	P/N ?	TOTAL
10	6	6	0	6	0	12
13	8	7	0	8	0	15
10	5	5	0	5	0	10
11	6	5	0	6	0	11
14	5	6	0	5	0	11
11	7	6	0	7	0	13
7	3	4	1	2	0	7
76	40	39	1	39	0	79

Counting Bumblebees in Winter

After watching buff-tailed bumblebees (Bombus terrestris) visiting flowers for the last three winters in Falmouth I have gained some insights into their behaviour but many questions remain. Discovering a nest a week ago will help extend that knowledge a little further. By counting the bumblebees leaving and returning to the nest it is possible to speculate how many bees are in the nest. 

Friday 24th February 2017 Bombus terrestris nest - Falmouth, UK 
P/N? = unable to distinguish whether bee had pollen due to hind legs obscured

TIME	DUR MINS	BEES IN	BEES OUT	POLLEN	NECTAR	P/N ?	TOTAL
14.36	12	16	10	5	8	3	26
14.49	10	9	9	4	5	0	18
15.01	10	6	7	1	4	1	13
15.12	10	16	9	5	6	5	25
15.26	10	5	6	0	3	2	11
15.40	11	5	4	2	2	1	9
15.54	11	5	6	4	0	1	11
16.06	6	6	0	1	3	2	6
TOTALS	80	68	51	22	31	15	119

The first thing to consider when looking at the numbers is that about 60% of the worker bees in the colony will remain in the nest doing such things as helping care for the young.

A rule of thumb guide is to take the number seen in ten minutes and times that by four. Taking the peak result would give us 104 bees in the colony with about 42 of these involved in foraging. As can be seen the activity decreased over the time of observations illustrating how varied foraging activity can be. Taking an average of the 10+ minute numbers gives a colony size of 66 bees with 26 workers foraging.

As a ballpark figure we have a colony size of 66 to 104 bees from the initial observations.

Edit 17th December 2017 - Having reflected on these figures I feel they are probably too low. Given that there are fewer flowering plants in winter it is likely foraging flights take longer. Also the frequency of bees visiting plants in various locations suggests a larger colony size although the possibility of there being more than one colony must be considered.

The question is only really going to be answered with a spade once a colony has completed its lifecycle and is disused. Examining winter active nests and looking at its cells where the larvae turn into adult bees will not only give accurate numbers but also answer how many males and queens were produced. 

If you are imagining me standing over the nest for eighty minutes counting the bees while examining each to see if they were carry pollen, possibly wearing a deerstalker hat and smoking a pipe you are mistaken. I filmed the nest - the breaks between counts was due to moving the camera and reframing. Counting was done in the warm, watching and replaying the video while drinking copious cups of tea.

Of course I could not resist making another bumblebee video from 80 minutes of footage - don't worry it is only 2 minutes long.

A rare discovery - winter active bumblebee nest

Most bumblebee queens hibernate during the winter however towards the end of the 1990's a few winter sightings of Buff-tailed bumblebees (Bombus terrestris) workers were recorded. Winter colonies had previously been known from New Zealand where the species had been imported.

The buff-tailed bumblebee is our most common species but even so winter activity is only known at a few locations in the UK. From the distribution of records the availability of winter flowering plants seems as important as climate if not more so - none have been recorded further north than Hull*.

With few sightings there is still much to be discovered about these winter colonies. For example it is not known how many colonies that produce workers in December and January successfully complete their life cycle - see earlier post, Missing male bumblebees - a mystery?

Although I have been observing Buff-tailed bumblebees in Falmouth for the last three winters the odds of finding a nest were slim. In the end it turned out to a mixture of luck meeting a prepared mind. I sort of stumbled upon it but knew immediately what I had found.

How rare a find is it? To my knowledge the earliest winter nest (December through to February) was discovered in London last December and that is still active to date**. Brigit Strawbridge observed new queens carry pollen back to their old nest in late November 2011 but no males were seen. This was a very late nest to be active, not typical behaviour and possibly a second generation brood. See my post, Bumblebees - A Winter's Tale for more information on second generations. There is also the possibility that the new queens may have founded nests themselves rather than hibernate.

There is still much to learn about this winter activity and it is possibly variable from location to location and year to year. People continue to see winter active workers such as Philip Strange, who has seen them in Paignton for the second winter running.***

Even though the video above is an edited highlights of arrivals and departures it is clear this nest has been established for some time. How long would be a guess but possibly it might be the nest of the workers I began observing in December.

In the video you can see the bees are bringing back different coloured pollen this shows that they are visiting different species of flowers. From the data I collected while filming and intend to collect on my next visit it should be possible to estimate of the size of the colony.

It will be interesting to see how long the colony remains active, current thoughts are that it will reach its end soon but I am keeping an open mind. Towards its end new queens are produced and as they often return to the nest they will hopefully be easier to observe. Males unfortunately leave never to return, indeed recent research suggests they do not remember the location of their nest. I am going to need a bit more luck to spot them.


* See BWARS 2010 infosheet here Click

** Literally a hour after posting the blog I read that the colony was still active (there had been no news of it since December) and have revised this post.

***Read Philip's blog for details of the winter active bumblebees in Paignton.      Click Here

  

Bumblebees - A Winter's Tale

Nature loves variation; evolution can be thought of as playing, let’s try something different and see if it works. Not only has this produced an astonishing variety of species it also results in variations within specie. Nature plays dice and making general statements is often a bit of a gamble. Quite often there are exceptions that complicate matters.

The bumblebee is a good example of this for while most have a life cycle of one generation in a year there are exceptions. Generally new queens emerge in late summer, they will mate and then forage for food to build up their reserves before digging a burrow that they hibernate in.

Upon emerging the queens feed on nectar while their ovaries mature and then begin to search for a suitable nesting site. Once she has established a nest she will lay the first batch of eggs to produce female workers. Bees can determine the sex of their eggs as fertilised eggs produce females and non-fertilised eggs males. The queens sit on their eggs and it is thought that temperature can influence the size of the workers. Warmer eggs producing larger larvae. The amount of food they consume is also likely to determine their adult size.

The queens forage for nectar and pollen to take back to the nest for their larvae to feed on. The larvae eventually spin a cocoon from which they will emerge as adult worker bees. Once enough workers have been produced to bring an adequate amount of pollen and nectar back to nest the Queen no longer leaves it.

 

Eventually the point is reached where the queen starts to lay male eggs and females to become queens not workers. Up to this point the queen has been releasing pheromones to suppress the female workers from becoming fertile and laying their own eggs. As she now wants to produce eggs that will develop into fertile queens she ceases to produce the phoromones. Without them the social order of the nest breaks down and some of the workers will attempt to lay their own unfertilised eggs to produce males. In many cases the unrest within the nest will lead to the workers stinging the queen to death.

The adult males leave the nest in search of queens to mate with. With their own nest in a state of turmoil they are homeless and fend for themselves. If on a rainy late summer’s day you see a wet bedraggled bee it is likely to be a male. In their search for newly emerged queens from other colonies they can travel up to 10km from their original nest.

This brings us back to where we started and the general life cycle of a bumblebee colony is completed - now for some exceptions.

Let us start with the Early Bumblebee (Bombus pratorum) as in this country there is geographical divide in the behaviour of queens. In the North pratorum follows the life outlined above. In the South though some of the new queens produced in a year rather than hibernate will establish nests to produce a second generation in the same year. It would be easy to assume that the difference is due to the climate. That spring arrives earlier in the South and frosts later. It sounds sensible but some bumblebees in Norway challenge that idea.

The Hearth Bumblebee (Bombus jonellus) is found both in this country and Norway. In this country like Bombus pratorum in the south it can produce two generations in a year and the same is true in Norway. Not only that but the subspecies, Bombus jonellus sub borealis occasionally produces two generations in Troms county, Norway that is north of the Artic Circle. Length of season does not of itself seem to be determining whether a queen produces a second generation or hibernates.

In the U.S.A. it seems three species in Oregon can produce a second generation in a single year. These are the yellow faced bumblebee (Bombus vosnesenskii), the fuzzy-horned bumblebee (Bombus mixtus) and the black-tailed bumble (Bombus melanopygus).

Studies in Norway and the U.S.A. suggest mild and dry summer that result in an abundance of suitable flowers species in late summer is a key factor in motivating some bumblebee species to produce a second generation.

Winter active bumblebees are another exception to the general behaviour of bees in this country. These are queens who establish a colony with workers that are foraging through the winter months. For several years winter active Buff tailed Bumblebees (Bombus terrestris) colonies have been recorded mostly in southern urban locations but with outliers as far north as Hull. In locations where this occurs it seems to become a regular occurrence. This is the third year where I have recorded winter active terrestris in Falmouth. This year for the fist time I also found Garden Bumblebee (Bombus hortorum) workers on the same Mahonia flowers as terrestris workers. This mirrors evidence from New Zealand where we exported both species in the 19th Century. There terrestris is the most common winter active species with hortorum less frequently seen. Another exported species Bombus ruderatus has also been recorded as being winter active there, it will be interesting to see if this eventually happens in this country.

It is not known what prompts a new queen to hibernate. Most enter hibernation before the arrival of cold weather, so temperature appears not to be a trigger. It may be that once a queen has built up her reserve being in a burrow is the safest place for her. Combining the time spent in their hibernation burrow with that spent in their nest suggests that queens have a preference not to be out in the open. Most of a queen’s life is spent sheltered and protected.

Generally the instinct to hibernate after mating and building up their reserves is strong in queens of all species. As the exceptions show the strength of the instinct is variable in at least a few species. Going against the norm is a gamble. For example a queen that begins a colony in the late autumn will be reliant on the availability of flowering plants throughout the winter. In the right urban location the odds of survival are favourable elsewhere they are bleaker. 

Another potential problem faced by a bumblebee colony that breaks the widespread timings of their species' lifecycle is finding mates for their males and queens when most of their species are unavailable. A small isolated population can be susceptible to inbreeding.

Variability within a species offers the possibility of adapting to change and taking advantage of new opportunities. If all of life is a gamble then spreading your bets is the safest option.