Bumblebees of the World Blog Series… #6 Bombus rupestris

Natural History Museum Bombus – Bumblebees of the world homepage

Richard Comont’s RSPB Spotlight bumblebees (2017)

Acknowledgements

Many thanks to Paul Williams of the Natural History Museum, London, for his help and advice.

Male Bombus inexspectatus by Maurizio Cornalba

Bumblebees of the World Blog Series… #7 Bombus inexspectatus

A male Unexpected bumblebee, Bombus inexspectatus

Latin name: Bombus inexspectatus

Common name/s: Unexpected bumblebee

Colour pattern: Males and females have two yellow bands on the thorax, a yellow band at the top of the abdomen and a red tail. The host species (Bombus ruderarius) mainly occurs with similar pattern to the British type (unbanded with a red tail), but can also have similar banding to the Unexpected bumblebee, although the back of the head is larger in B. inexspectatus than B. ruderarius in both males and females.

Host species: Red-shanked carder bee (Bombus ruderarius)

Favoured flowers: Females have been found on Clovers and Rampions, males on Knapweed and Thistles

Global region: Palaearctic

Geographic distribution: Europe – Alpine regions of France, Switzerland, Austria and Italy, and a disjunct population in the Cantabrian Mountains of Spain.

Conservation status: Endangered

When Tkalcu first made his discovery of a new/overlooked European bumblebee species it prompted European bumblebee specialists to resample potential locations and look back in their own collections to reassess potential specimens. As a result, the original four records soon became eighty or so. Interestingly, the original records included two males and two supposed workers, which happen to be the only two workers ever found for this species. The status of these females as workers was called into question by Yarrow in 1970 who proposed that inexspectatus could potentially be a social parasite of the closely-related Red-shanked carder bee (B. ruderarius), which he always found in good numbers wherever inexspectatus was found. He argued that the workers were merely ‘runt’ females which were underdeveloped in comparison to the rest of the female specimens. Close examination of collected specimens revealed that unlike social bumblebees and similar to cuckoos, inexspectatus specimens do not appear to secrete wax from their abdominal segments, which is an essential part of colony building among the social bumblebees. Yarrow noted that none of the specimens he had seen had any evidence of pollen collecting, and that the structures on the legs associated with pollen collection seemed to have degenerated slightly in comparison with social bumblebees, although not to the same extent as the main cuckoo group (Psithyrus subgenus).

It was not until 2005, when Andreas Muller and colleagues stumbled upon a Bombus ruderarius nest in the Swiss Alps, that Yarrow’s suspicions were supported with the first and only evidence of parasitism by inexspectatus. The nest they found was close to completion with no stored nectar, eggs or larvae, a selection of empty cocoons from various generations of workers and four unhatched cocoons, which four ruderarius queens later emerged from. No founding queen/females of either species were found, however two ruderarius workers, two males and one new queen remained in the nest when it was found, as well as one fresh inexspectatus female. This indicated that both the social queen and the parasitic female were co-existing in the nest, which has been found when other cuckoo bumblebees invade nests, but often the social colony does not successfully produce new queens or produces fewer than normal. As this is the only nest that has been found to date – we do not know how common it is for the two species to co-exist or if the invading bees manage to completely take over nests in the same way that some other cuckoo bumblebees do. There are also larger questions about this species’ general ecology and life history still to be answered, for example, whether inexspectatus can invade the nests of other hosts, similar to the other known parasitic bumblebee species.

Links to further information:

Natural History Museum Bombus – Bumblebees of the world homepage

Hines, H. M., and Cameron, S. A. (2010). The phylogenetic position of the bumble bee inquiline Bombus inexspectatus and implications for the evolution of social parasitism. Insectes Soc. 57, 379–383. doi: 10.1007/s00040-010-0094-1

Müller, Andreas. (2006). A scientific note on Bombus inexspectatus (Tkalců, 1963): Evidence for a social parasitic mode of life. Apidologie. 37. 408-409. 10.1051/apido:2006005.

Yarrow I.H.H. (1970) Is Bombus inexspectatus (Tkalců) a workerless obligate parasite? Insectes Soc. 17, 95–112

Acknowledgements

Many thanks to Maurizio Cornalba of the University of Pavia, Italy, and Paul Williams of the Natural History Museum, London, for their help and advice.

Allotment wildflowers by Katy Malone

Bees find a helping hand on my allotment

Allotment with many colourful wildflowers

23 July 2019

by Katy Malone, Bumblebee Conservation Trust Conservation Officer for Scotland

Being a fully paid-up member of the bumblebee fan club, no-one will be surprised to learn that when I finally got offered an allotment in my village three years ago, I set out to make it as bee-friendly as possible. After all, growing veg and attracting crop pollinators with nectar and pollen-rich flowers – well, it’s just a no-brainer.

That said, my fellow allotmenteers and I each have our own distinctive style of growing, which probably reflect our personalities. The gentleman with the plot next door to mine grows very traditionally in very neat, die-straight rows. Potatoes are earthed up in immaculate V-shaped furrows, all the same height and distance apart. He plots out carrots in a millimetre-accurate grid. Every scratch of ground is used for crops of some sort. One a sunny day in May, he spotted the packets of bulbs I brought for planting in the pre-prepared ground and was intrigued.

“Oh, what’s that you’ve got?”

“Gladioli blubs – a lovely mixture of…”

…but he had already turned away in pretend disgust. Of course, I was letting the side down! We joked about it, but I know he’d really prefer me to be grow swedes rather than ‘wasting’ the available space with flowers. He still borrows my rake when I’m not around though.

The plot opposite has lots of flowers as well as crops, in higgledy piggledy rows. She’s a child minder, and her young charges often come down to help her in the allotment. She grows lovely sweet peas, lilies and cosmos, the veg and the flowers being mostly separate from each other.

My own plot is something of a potager style, with blocks of edible crops interspersed with colourful flowers which attract pollinating insects like bumblebees (of course!) as well as honeybees, wasps, and hoverflies. I get a great sense of satisfaction by growing from seed, and this year almost all my crops are grown this way (except potatoes from sets, and garlic which I grew from cloves saved from last year’s crop).

Cornflowers, self-sown foxgloves and cosmos all attract a variety of beneficial insects. The cornflowers are part of my plan to grow flowers for cutting, but if an insect happens to be feeding on the freshly emerged flower, I leave it alone. I would feel so guilty for depriving any bee of its lunch! If a few crops start bolting, and I don’t need the space immediately, I’ll let them flower. The hoverflies are particularly keen on the towering blooms of Swiss chard, which bloom profusely before flopping over in the wind and need to be propped up or cut back.

Some ‘weeds’ are particularly beneficial and I let them grow amongst my veggies, as long as they don’t start to take over. Red dead-nettle is a favourite with long-tongued bumblebees, which in turn are brilliant pollinators of my runners and broad beans. The shorter-tongued honeybees and hoverflies can’t reach the nectar in these long-flowered crops, and so cannot pollinate them. Encouraging longer tongued species like garden bumblebee and common carder bumblebees by providing a greater diversity of long flowers is good for a quality crop set. I know there are modern F1 crop varieties which are self-setting, but I prefer to grow open-pollinated heritage varieties. For me, it goes against the grain to do anything else.

It would be great to think that all this results in better pollination of my crops – and really, I have no first-hand evidence that supports that. However, a research paper1 published in Nature earlier this year revealed that allotment sites are very valuable spaces in an urban context. The researchers showed that residential gardens and allotments in four different cities across the UK were major hotspots for pollinators, highlighting the value of these places for supporting vital pollinator conservation. In his regular summary of recent science papers ‘Bombus Review’ (Bombus review – Spring 2019) my colleague Darryl Cox wrote of this paper:

“The authors end their report with some really useful and practical suggestions for maximising the pollinator potential of urban areas. They suggest that town planners try to add more allotments to towns and cities as even a small area increase could make a big impact on the robustness of plant-pollinator communities.”

Watching bees work those multi-coloured cornflowers, benefitting from the abundant nectar and pollen from the red dead-nettle and enjoying the late boost of forage from the gladioli and self-sown foxgloves gives me satisfaction beyond words. When I’m enjoying freshly-podded broad beans, lightly steamed with butter and parsley and a squeeze of lemon, I am even more glad to be supporting the bees in my little corner of paradise.

A systems approach reveals urban pollinator hotspots and conservation opportunities. Baldock, KCR et al, Nature Ecology & Evolution volume 3, pages 363–373 (2019)

A brief guide to solitary bee nest boxes

Bex Cartwright, our Making a Buzz for the Coast Conservation Officer, has written this handy guide on how to create or choose a suitable bee box to make a perfect home for solitary bees in your garden!

A bee box for solitary bees attached to a garden fence

Credit: Bex Cartwright

Siting your solitary bee nest box

To maximise the chances of your solitary bee nest box being occupied, careful siting is important.

Position your nest box in full sunshine so facing south east or south
Place the nest box at least 1 metre from the ground
You can place your nest box near vegetation but ensure that no vegetation will obscure or shade the nest entrances
Position the nest box in a stable, fixed position that will not sway in the wind or be easily knocked or dislodged.
Remember, one of the reasons for having a bee nest box is so you can observe the fascinating activities of the solitary bees visiting your garden so make sure it is somewhere you will see it regularly.

A leaf-cutter bee entering the hollow tubes of a solitary bee hotel.

Credit: Alison Scimia

Things to consider when choosing or creating a solitary bee nest box

If you are thinking of creating a new bee nest box or buying one of the many commercially available nest boxes there are a number of things to consider. Many are expensive and some are poorly-designed. Some of the most commonly encountered issues are:

The length of the nesting tubes or drilled holes is not sufficient. Look for a nest box with nesting tunnels 15cms in length as a minimum.
The diameter of the nesting tubes are often too wide. This is because houses manufactured abroad are built to attract larger species than those we have in the UK. It is beneficial to provide a range of diameter nesting tubes as this will attract a range of different species. Provide holes of between 2-10mm in diameter.
No protection from wet and windy weather. Ideally the bee house will have a small overhang to prevent nesting tubes becoming damp. To some extent this can be alleviated by careful placing of the bee house. Somewhere sheltered but not shaded is ideal.
Avoid the use of plastic straws or containers. Plastic and other ‘non-breathable’ materials prevent the movement of air and moisture and can encourage damp and condensation leading to fungus and mould. This will destroy eggs and larvae.
In general tunnel and tube entrances should be smooth and free of splinters although some species will clean out and ‘tidy-up’ a tube before nesting.
Nesting tunnels and tubes should have a solid back. Bees will not use nesting tubes which are open at both ends.
The nesting tunnels need to be accessible and removable so that the contents can be examined, cleaned and periodically replaced. The most successful bee nest boxes are those that are well-managed.

A female Patchwork leaf-cutter bee flying while holding a small leaf between its legs.

Credit: Jean Baird

Which bee species will the nest box attract?

The most common resident of garden bee nest boxes is the Red Mason Bee (Osmia bicornis), this species flies in early spring. Later in summer your bee nest box may also attract leafcutter bees such as Patchwork Leafcutter (Megachile centuncularis) (image above) and Willughby’s Leafcutter (Megachile willughbiella). These species play host to cuckoo bees Coelioxys, also known as ‘sharp-tailed bees’ (image right), fascinating bees which lay their own eggs in the provisioned leafcutter nests. Smaller bees such as Harebell bees (Chelostoma sp.) and Masked or Yellow-faced bees (Hylaeus spp.) are also attracted to nest boxes

A range of solitary wasps may also use the nest box, these will act as a great natural pest control in your garden, collecting flies, small caterpillars and aphids to provision their nests.

Managing your bee hotel

Periodic maintenance and cleaning will result in a more successful nest box and a healthier population of bees in your garden. With no cleaning, fungi, debris and parasites tend to build up which can be damaging to the bees.

Bring your nest box into an unheated shed or garage during the autumn and winter to protect it from damp and wet weather. If you don’t have either then a porch or any covered area will do. It is damp not cold that destroys larvae. Not only will this protect the larvae and adult bees waiting to emerge in the spring but it will mean that your nest box will last longer. You can place the box outdoors in the spring, from March onwards.
If you notice birds predating your nest box or removing nest tubes (woodpeckers and tits often do this) then you can place a piece of mesh or chicken wire across the front. This does not appear to deter the bees.
If your nest box is built of stacked & routed wooden sheets or you use paper nest tube liners you can clean it out in winter, remove the cocoons (image left) and store them until spring.
At least every couple of years replace all of the tubes and blocks in the nest box with fresh ones. In spring leave the old tubes in an upturned box or bucket on the ground with a hole at the top (bees naturally orientate towards light) so that the previous year’s bees can emerge but so that they won’t reoccupy the old tubes.

For further information on all of the above Marc Carlton of ‘The Pollinator Garden’ has produced an excellent guide to ‘Making and Managing a Bee Hotel’. A pdf. version can be downloaded from www.foxleas.com

George Pilkington also has a fantastic website and blog ‘Nuturing Nature’ www.nurturing-nature.co.uk which has a wealth of information on managing bee houses.

For photos and more information about the bees and wasps that are attracted to nest boxes the website of The Bees, Wasps and Ants Recording Society ‘BWARS’ is very helpful www.bwars.com

Bombus fraternus by J C Jones

Bumblebees of the World Blog Series… #4 Bombus fraternus

by Darryl Cox, Senior Science & Policy Officer

The Southern Plains bumblebee (Bombus fraternus) features in this month’s Bumblebees of the World blog, with a particular focus on how the species’ endangered conservation status was classified by the IUCN’s Bumblebee Specialist Group (BBSG).

Fact File

Latin name: Bombus fraternus

Common names: Southern Plains bumblebee

Colour pattern: Queens and workers are predominantly pale straw-coloured yellow with a black band between the dark wings and an extensive black tail. Males look similar, although can be more extensively yellow between the wings and have very large eyes.

Favoured flowers: Milkweed (Asclepias), Prairie clovers (Dalea), Blazing stars (Liatris), Sweet clovers (Melilotus), Prairie coneflowers (Ratibida) and Goldenrod (Solidago)

Global region: East Nearctic region, West Nearctic border

Geographic distribution: North America – Central to South-eastern US (Virginia, Texas, Minnesota, Massachusetts, Louisiana, Kansas, Iowa, Indiana, Illinois, Georgia, Florida, Colorado, Arkansas, Alabama, Mississippi, Missouri, Nebraska, New Jersey, New Mexico, North Carolina, North Dakota, Ohio, Oklahoma, South Carolina, South Dakota, Tennessee)

Conservation status: Endangered

The Southern Plains bumblebee is found to the east of the Rockies, across the prairie lands in the south of the Great Plains, stretching to the coastal plains of central Florida and New Jersey. With pale yellow and black banding, this short-tongued bumblebee has a similar colour form to a number of North American species, however it is has a very distinctive look, with extremely short and even hair across its body. This gives the bee a very close-cropped and neat look overall – almost like a bumblebee with a (forgive me) buzz cut! Some of the hair on the abdomen is completely flattened to the body making the abdomen look slim and sleek in comparison to other fuzzier bumblebees.

The IUCN-BBSG last assessed the conservation status of this species in 2014, when it was classified as endangered. Their justification came down to three main factors – relative abundance, which is a measure of how many records of this species there are in relation to the total number of species recorded, a change in its extent of occurrence, which relates to the species’ overall distribution, and the loss of suitable habitat within the species’ known range.

The IUCN-BBSG team took historical national bumblebee records and plotted the Southern Plains bumblebee’s relative abundance at 10 year intervals to understand how it had changed from 1912 to 2012. The figure below shows a historical downward trend which is close to being statistically significant. If the trajectory were to continue at this rate, the assessors warn the species could potentially be extinct within the next 80-90 years.

The decline in relative abundance since 2002 was consistent with a decline in distribution. The team mapped historical records and compared them with records post 2002 to understand the extent that the species still occurs across its known range. After taking care to avoid statistically overestimating range loss (by randomly rarefying the much larger number of pre-2002 records), they found that the species had reduced its area of occupancy by 28.62% since 2002. A heat map depicts the amount of surveying that took place between 2002 and 2012. This shows that some of the areas the species has declined from have also been well surveyed in recent times, which gives the team confidence in their assessment that Bombus fraternus has declined in range.

The third area of justification relates to severe changes that have occurred in the Southern Plains bumblebee’s habitat range, particularly since 2002. This period has seen native grasslands converted into agricultural land and increased use of agricultural pesticides. Identifying the negative impact that these changes have had is useful as it helps indicate what needs to change for this species to recover. The IUCN-BBSG identify the following general actions to conserve Bombus fraternus: restoring, creating and preserving natural grasslands, restricting harmful pesticide use within or close to their habitats, and protecting them from diseases introduced by managed bees. However, more research is needed to fully understand the specific requirements of this distinctive species and how best to help it. For those wishing to get involved with Bumblebee Conservation in the U.S. check out the IUCN Bumblebee Specialist Group.

Links to further information:

Natural History Museum Bombus – Bumblebees of the world homepage

The Bumble bees of North America: An Identification guide. By Williams, P.H., Thorp, R.W., Richardson, L.L. and Colla, S.R. (2014) Princeton University Press, Princeton

Xerces Society Bumblebee conservation page

Acknowledgements

Many thanks to Paul Williams of the Natural History Museum, London, for his help and advice.

Bombus cullumanus by Natural History Museum, London

Bumblebees of the World Blog Series… #5 Bombus cullumanus

Cullum’s bumblebee, Bombus cullumanus pinned as a museam exhibit

by Paul Williams, Researcher at the Natural History Museum, London, and Darryl Cox, Senior Science & Policy Officer.

This month, Bumblebees of the world returns from across the Atlantic to feature Cullum’s bumblebee (Bombus cullumanus), a Eurasian species which is sadly no longer found in the UK and has experienced drastic declines across the rest of Western Europe.

Latin name: Bombus cullumanus

Common name/s: Cullum’s bumblebee

Colour pattern: In Western Europe, queens and workers are black with red tails and look very similar to Red-tailed bumblebees (B. lapidarius), although queens are smaller and sometimes have a very faint yellow band that can be seen at the collar.

Males have a dull yellow collar and bands across the lower thorax and majority of the upper abdomen with a red tail (similar to some brighter Ruderal bumblebee (B. ruderarius) males).

Favoured flowers: older male specimens are described as feeding on Knapweed, White clover, Wild marjoram, Musk and Dwarf thistles. Workers are thought to favour legumes.

Global region: Palaearctic

Geographic distribution: Europe – Moldova, Montenegro, Romania, Russia, Serbia, Spain, Ukraine. Asia – Russia, Turkey, Armenia, Iran, Afghanistan, Uzbekistan, Turkmenistan, Tadzhikistan, Kyrgyzstan, Kazakhstan, China, and Mongolia.

Conservation status: Critically Endangered in Europe

Cullum’s bumblebee, named after 7th Baronet, Sir Thomas Cullum, a medical doctor and well-respected natural historian from Suffolk, was described as new to science by William Kirby in 1802 after an interesting striped and red-bottomed male was spotted in Suffolk. It was not until 1926 that the connection was made between the yellow-banded males and the black females with red tails, which are difficult to separate from the similar, more widespread Red-tailed bumblebee (Bombus lapidarius).

Bombus cullumanus belongs to a broader species group of closely related species known as the cullumanus-group. The species group has been the source of much debate amongst taxonomists and there have been several interpretations of the number of species within the cullumanus-group, but DNA barcoding has been able to provide a much clearer answer.

It turns out that Cullum’s bumblebee can be exceptionally variable in terms of colour pattern and because of this it has been classified as several separate species from different geographic locations. Williams et al. (2012) set out to sequence the DNA of some bumblebee specimens within the cullumanus-group and found that four bumblebees which had been classified as separate species are actually parts of Bombus cullumanus, which is known to be declining steeply in Western Europe (described in the fact file). The following ‘species’ have therefore been reclassified as parts of Bombus cullumanus:

Bombus serrisquama – a yellow banded bumblebee found in Spain, Russia and Central Asia
Bombus apollineus – a white banded bumblebee found in Turkey and Armenia.
Bombus tenuifasciatus – darker yellow bands found in Central Asia
Bombus nigrotaeniatus – also Central Asia and with no yellow band on the abdomen

The last confirmed sighting of Bombus cullumanus in the UK was a male on the Berkshire downs in 1941, making it one of two species that have likely gone extinct from the UK in the last 80 years (the other being the Short-haired bumblebee, Bombus subterraneus). It has similarly vanished from the Netherlands, Belgium, France, Germany, Sweden and Denmark.

Although this is undeniably sad news, the new understanding that the species is much more widely distributed than initially thought (albeit in different colour forms) means that in conservation terms, it is doing better than initially feared, especially in Russia and Central Asia where it can be common in grasslands. In fact, the genetic work by Williams and colleagues indicated that another species within the wider cullumanus-group, Bombus unicus, may actually be worse off. They are calling for urgent surveys to help assess the status of Bombus unicus, which seems restricted to the far East of Russia and has only ever been found in very low numbers.

Links to further information:

Williams, P.H., Byvaltsev, A., Sheffield, C., Rasmond, P., Bombus cullumanus—an extinct European bumblebee species? Apidologie (2013) 44: 121.

Natural History Museum Bombus – Bumblebees of the world homepage

Bombus dahlbomii by Michael Usher

Bumblebees of the World . . . #1 Bombus dahlbomii

The Patagonian bumblebee or Flying Mouse, Bombus dahlbomii, feeding on a flower

by Darryl Cox, Senior Science & Policy Officer

There are around 250 species of bumblebees across planet Earth, stretching across most of the Northern Hemisphere, from the arctic, right down to the southern-most tip of South America in the Southern Hemisphere. Each bumblebee species has a different distribution and all are an important part of life within their ecosystems. By transferring pollen that helps plants set fruit and reproduce, they are involved in the base layers of numerous food chains, which provide food and shelter for a great multitude of living things (including ourselves).

This year, we have decided to show our appreciation for some of the most beautiful and diverse bumblebees from across the world in our monthly Bumblebees of the World blog series, and what better way to start our series than with one of the world’s largest and most iconic bumblebees: Bombus dahlbomii.

Fact File

Latin name: Bombus dahlbomii

Common names: Patagonian bumblebee, Flying Mouse

Colour pattern: Deep orange/ginger thorax and abdomen, with black underside, legs and wings. (Queens, workers and males)

Favoured flowers: Chilean bellflower (Lapageria rosea), Peruvian lily (Alstroemeria aurea)

Global region: Southern Neotropical, Eastern Neotropical

Geographic distribution: South America – Chile, Patagonia, Argentina

Conservation status: Endangered

Commonly known as the Patagonian bumblebee or the Flying Mouse, the South American Bombus dahlbomii is a giant among bumblebees. With queens that can grow as large as 3 cm long – you definitely know when you’ve seen one of these ginormous ginger bees! These majestic bumblebees are not only iconic based on their size, they are also known globally for their story, which sadly, is one of human-caused decline.

The decline has been rapid and can be attributed to the introduction of two non-native invasive European bumblebees, Bombus ruderatus and Bombus terrestris. These bees were originally imported to Chile for commercial pollination in agriculture. In 1982 and 1983, hundreds of Bombus ruderatus queens were brought over from New Zealand (from the population originally exported from the UK in the 1800’s) to aid with pollination of red clover, which subsequently led to their invasive establishment in the wild. Bombus terrestris colonies are still regularly imported into the country, where they are deployed in greenhouses and in open fields to pollinate tomatoes, avocados and blueberries. Astonishingly, since 1997, over a million colonies of Bombus terrestris have been imported into Chile. They are now firmly established in the wild and have invaded Patagonia and Argentina.

Not only do these invasive bees compete for food resources, but they have also brought novel diseases with them which have likely had a profound negative impact on the native species, much like when the Spanish unleashed a host of new human diseases on the native South American people throughout their colonization of the Americas. Unfortunately for Bombus dahlbomii, the consequences of this introduction have been great and the species is now classed as internationally endangered. Sightings of the legendary Flying Mouse are now much rarer across its once large distribution in southern South America; it has all but disappeared from the north of its known range, coinciding with the range expansion of the two invasive species. With Bombus terrestris expanding further and further south, there is grave concern that Bombus dahlbomii may not be far away from extinction. This is not only bad for Bombus dahlbomii, but also has wider ecological consequences for the plants it pollinates, many of which are now subject to nectar robbing by the alien species, and also means that non-native invasive plants, such as Scotch broom, are able to spread as their preferred European pollinator is now there to help them reproduce.

The damage caused by these alien bees entering South America is now irreversible because the alien species cannot be eradicated. However there are crucial lessons to be learned: animals do not respect international borders and so decisions made by one country’s government can have unintended consequence for neighbouring countries (in this case Argentina did not import non-native bumblebees). This has led scientists to argue for international cooperation on the global trade of species, something which is vital to prevent further cross-border invasions. The global commercial bumblebee trade has been growing rapidly over the last three decades and it is imperative that governments, traders and farmers act responsibly to avoid the consequences of allowing commercial bumblebees to freely enter non-native environments.

Links to further information:

Natural History Museum Bombus – Bumblebees of the world homepage

British Ecological Society Article

Aizen et al. Coordinated species importation policies are needed to reduce serious invasions globally: The case of bumblebees in South America (Journal of Applied Ecology)

Acknowledgements

Many thanks to Paul Williams of the Natural History Museum, London, for his help and advice.

Bombus transversalis by Mongabay

Bumblebees of the World Blog Series… #2 Bombus transversalis

A South American Bumblebee, Bombus transversalis

by Darryl Cox, Senior Science & Policy Officer

This month our bumblebee world tour stays in South America, although we are heading north from Patagonia into the Amazon basin, where our species in the spotlight is the Amazonian bumblebee, Bombus transversalis.

Fact File

Latin name: Bombus transversalis

Common names: None

Colour pattern: Queens and workers are black with two bright golden-yellow bands on the thorax, one yellow band towards the rear of the abdomen and a black tail. Males have similar banding, although the yellow is paler and the bands are more extensive on the thorax.

Favoured flowers: Unknown

Global region: Western Neotropical, Eastern Neotropical

Geographic distribution: South America – Brazil, Bolivia, Colombia, Ecuador, Peru

Conservation status: Least concern

Bombus transversalis is an impressive Amazonian specialist which exists in the tropical rainforests and wet lowlands of the Amazon basin. One of the most fascinating things about this species is its ability to survive and thrive in the most challenging of environments. Most bumblebees living in the tropics are known to operate at cooler, higher altitudes, and with good reason, the Amazon basin is well known for tropical temperatures, near maximum humidity and receiving copious amounts of the wet stuff (they don’t call it a rainforest for no reason)! Given that bumblebees evolved in temperate regions, it’s not hard to see then, that nesting on the rainforest floor is possibly one of toughest tasks for any bumblebee species on earth. Even if they can successfully avoid being flooded and washed away, they then have to raise their young in extreme temperatures and high humidity, compete for food in one of the most biodiverse places on the planet, and evade predation from numerous potential foes, including army ants!

To deal with these challenges Bombus transversalis must build a unique nest. The first step is for the nest-searching queen to find the perfect spot – she needs somewhere on dry land that is unlikely to flood and has some existing structures of roots and shoots. These structures are vital foundations for the queen and her new colony to build their home around – a construction which must be able to withstand daily deluges and an annual precipitation rate of up to 3000 mm. To make the site waterproof Bombus transversalis workers engage in a unique behaviour of foraging for leaves, often by sweeping short trails or areas in pairs. Using their mandibles, they then cut the leaves into manageable pieces and weave them into a roof canopy around the existing supports. The end result is a large dome of interwoven leaves which is nicely camouflaged among the leaf litter of the rainforest floor. This thick thatched roof prevents water from getting in, and also means that potential predators like army ants must come through the sole opening, where they will be faced with several guards.

Professor Sydney Cameron who has spent time studying these fascinating bumblebees described the above nest in detail: ” The size of this particular nest canopy is 86cm left-right, 69cm front-back, 35cm high and 5cm thick. It is constructed of leaves, small twigs and rootlets, interwoven to fashion a conical protective canopy, which covers the brood beneath. It is entirely waterproof and constructed by a behavioral caste of workers, who also maintain the nest canopy, keeping it clear of debris that may fall from above. Note its striking resemblance to some formicine (wood ant) nests.”

Inside the nest there are more leaf layers to the canopy and an ingenious air space before the last layer which allows the bees to control the humidity, leaving the internal chamber completely dry and perfect for incubating brood. Colonies which get this bit wrong have damp nests which are prone to fungal growth. Constant temperature management is key and there will often be bees positioned at the edge of the nest using their wings to fan cool air inside to prevent the nest from overheating.

Successful colonies grow to full strength during the wet season and switch to rearing new queens and males once the dry season begins. Although their life-cycle is seasonal with colonies dying out during the dry season, their nest sites are often so well-built that they remain in place for several years. As such it is not uncommon to find a new queen starting a new colony in a pre-existing nest – something which is fairly unusual for most other bumblebees, but likely gives Bombus transversalis queens a great advantage in the Amazon.

Bombus transversalis is a true pioneer bumblebee species. Through its unusual nest construction, it has managed to survive in one of the toughest places to live on earth.

Links to further information: