Bees in the demolition business

By Athayde Tonhasca

The Capayán ruins in Argentina’s La Rioja province are the remnants of a settlement from the colonial period in the late 17th century. This historic site has resisted the ravages of time and weather – the region is very dry – but is threatened by a seemingly harmless resident: the bee Centris muralis.

Ruinas de Capayán, La Rioja, Argentina © World Orgs

This solitary bee is endemic to Argentina, and like other species of the genus Centris, is common in deserts and arid areas, and active when other bees hide from the heat. Some Centris bees are known as ‘digger bees’ because they build their nests in the soil, sometimes in barren patches with no vegetation. So the soft, dry adobe walls in the Capayánruins turned out to be excellent nesting sites for C. muralis – muralis, by the way, meaning ‘of walls’ in Latin.

Centris muralis bee © Vivallo, 2013. Zootaxa 3683: 501-537

The bee’s choice of residence doesn’t bode well for the Capayán archaeological site. Initially, a C. muralis female makes small holes in a wall, which are used by other females to get in and construct their own nests, each comprising several brood cells. With time, the number of cells reach densities of around 700/m2, which is way too high for the fragile structure. Ad in the erosive power of rain that seeps into the holes created by bees, and the walls slowly crumble away; some parts collapse. One particular wall lost over 700 kg of building material and its thickness was reduced by 7 cm thanks to the relentless work of C. muralis.

A damaged adobe wall from the Capayán ruins (a), and detail of a deteriorated area (b) © Rolón & Cilla, 2012. International Biodeterioration & Biodegradation 66: 33-38

Moving a long way north in the Americas, some home owners have their sights on carpenter bees (genus Xylocopa), which excavate holes in wood to build their nests. Any weathered wood will do, including man-made structures such as eaves, rafters, fascia boards, siding walls, decks and outdoor furniture. The effect of their excavations is mostly cosmetic, but significant structural damage can occur when the same area of wood is infested year after year. Carpenter bee holes also increase rot and decay. Persistent concentrations of carpenter bees may require home owners to control their numbers.

An eastern carpenter bee (Xylocopa virginica). Carpenter bees’ most obvious difference from bumble bees is the shining black abdomen ©, Wikimedia Commons. R: galleries of cells excavated by carpenter bees. Note the pollen-nectar loaves in several of the cells © Stephen Buchmann, US Forest Service

On this side of the Atlantic, the Davies’ colletes (Colletes daviesanus) and the red mason bee (Osmia bicornis)nest in holes and crevices, including in walls and mortar joints, sometimes in large numbers. These gatherings have prompted many a home owner to contract someone to get rid of bees that supposedly threaten building structures.

A Davies’ colletes © James K. Lindsey, Ecology of Commanster

Lack of information and misinformation are opportunities for easy money; remedies and fixes can always be bought, even when they are not the most appropriate or none are needed. So it is helpful – and cheaper – to know that these bees are hardly worth the bother. The red mason bee nests only in pre-existing cavities, while the Davies’ colletes can tunnel into soft mortar, especially in old walls. However, their excavating is limited to soft materials such as sandstone and lime mortars already weakened by age and weathering – which may need repairing anyway. A watchful owner can discourage extensive, repetitive burrowing by raking out the affected mortar and repairing the joints (repointing) with new mortar made with cement. Insecticides are not a good idea: they have limited effectiveness and may stain masonry. These are recommendations from The Society for the Protection of Ancient Buildings and English Heritage, which one would expect to take seriously any possible risk to historically important edifices.

Also, we can’t overlook the environmental roles of these bees. Centris muralis is an important pollinator in arid and semiarid habitats, where not many insects find an easy living. Carpenter bees are skilled at buzz pollination, i.e., extracting pollen by vibrating their flight muscles, so they are excellent pollinators of tomatoes, aubergines, and other vegetables and flowers with hidden pollen. The Davies’ colletes is a widespread pollinator of wild flowers, especially daisy-related species (family Asteraceae), while the red mason bee pollinates a wide range of plants, including several fruit trees.

An eastern carpenter bee carrying pollinia from milkweed (Asclepias sp.) © Beatriz Moisset, Wikiwand. R: a red mason bee dusted with pollen © bemma, Wikimedia Commons

The perceived threats from these building dwellers are a good example of conservation conflicts: clashes between nature and human interests. But like any other conflict, there is ample room for compromise, which starts by understanding and assessing the problem. Centris muralis is causing damage in an unusual setting, and perhaps no mitigation is possible. But the risks posed by the other digger bees are not great or can be alleviated. Judicious evaluations, a degree of tolerance and a gentle touch would prevent us from compounding the stress inflicted upon pollinators by our over-dominance of the planet. 

Now showing

“What’s blooming in the Battleby living wall just now?”, I hear you ask. Rather a lot it appears. The watering system has performed flawlessly, the waifs, strays and cuttings that Jim Carruthers stealthily introduced are taking nicely, and those plants that patiently awaited their turn in the spotlight are finally enjoying their moment.

Nevertheless, there are a few surprises.  For one we have fox and cubs.  Now that might have caused you to spill your tea and choke on your biscuit, but worry not I’m being mischievous.  The fox and cubs in question are Pilosella aurantiaca a rather lovely deep-orange flowering plant. It earns its unusual common reference from the fact that the open flowers sit alongside the buds – and this combination of colour and ‘family’ presence explains the quirky name.

It is ideal for the Battleby green wall as it has shallow roots, well-suited to the little pockets on the wall. It also likes being in full sun, so once more the Battleby structure scores highly on the desirability chart.

Herbs, we know, are fantastic for pollinators. Marjoram, thyme, mint, sage, rosemary … the list of beneficial herbs goes on. One herb in the Battleby wall which is thriving is chive. To be useful for pollinators you need to let them flower, and what a glorious sight their pinky, purple pom-pom flowers are. A huge draw for bumblebees they add a welcome contrast in the predominantly green living wall.

There is something near mesmeric about watching chives flower heads swaying in the wind, and they are a big draw for insects. They are of course a member of the garlic family.

Also providing a splash of potentially culinary colour are wild strawberries. This diminutive plant adapts well to the shallow pockets on the green wall, the lovely little white flowers are now being replaced by small shiny strawberries and what was a fairly dense green plant is transformed into one of the sparklier elements on show.

Around the base of the living wall a clump or two of viper’s bugloss has taken hold and it is another bee magnet. The bright blue flowers are bright and help explain the plant’s ‘blue devil’ nickname. It isn’t just bees that are drawn to viper’s bugloss, hang around and you are bound to see a variety of flies.

The popularity of another startlingly cheerful blue flowers seen around Battleby, borage (Borago officinalis), is down to the fact that they are laden with nectar, and have the rather appealing characteristic for bees of replenishing their supply of nectar very quickly. It’s popular with gardeners too as a companion plant, placed near tomatoes and strawberries it is said to boost pollination. 

Finally the roof of the Battleby Living wall has seen one of the planks of wood which form the fascia curl dramatically. This has exposed a cosy gap behind the fascia and an opportunistic queen wasp was quick to spot this potential nesting site.  It’s a good 8 feet or so up off the ground, but best to be aware if you are enjoying the sights (and sounds) of our Living Wall.

Tidings of Comfrey and joy

At this time of year if I want to photograph bees I often head for nearby clumps of comfrey.  Along the banks of the River Tay they are easy to spot, and a magnet for insects.  These stands of blue, and occasionally pink, white or purple, flowers are seemingly irresistible for bumblebees. 

Comfrey is one of those plants that enjoys a long association with people too.  The Romans and Greeks were known to have many uses for the hairy leaves which they believed could both stem bleeding and heal broken bones.  The word comfrey is said to have its roots in the Latin for ‘growing together’.

Today, however, it is likely to be gardeners who would sing the plant’s praises.  As a fertiliser it enjoys rave reviews. For those who enjoy composting it is a great resource and apparently lots of fun. Although from what I read it requires patience, as it performs best in a fairly slow composting fashion. 

The key to its composting credentials is as a rich source of potassium, making it suitable to nourish garden flowers and fruits, including tomatoes, which as every gardener will testify take a bit of feeding.

Although it begins flowering in May it is not unusual for profuse comfrey leaves to be around until the first frosts. Fast forward a couple of months and your ears will be reverberating to many a Christmas Carol, don’t make the mistake of thinking the lyrics in ‘God Rest Ye Merry, Gentlemen’ are saying ‘comfrey and joy’, it is I am assured ‘comfort and joy’. Though no doubt you will be anticipating some comfort and joy if your composting endeavours have gone well.

Others view comfrey, a member of the borage family, as a useful addition in the battle to control slugs. A patch of comfrey is seen by some as a ‘distraction plant’ to lure slugs away from more prized species. But spare a thought for the poor slug, there are many types in the UK and the number of species which are considered pests is in single figures, yet this gastropod is almost universally vilified 

Many of you will be familiar with the UK Pollinator Monitoring Scheme’s FIT Count (Flower-Insect Timed Count) and if you cannot find any of the 14 target flowers listed above you are free to choose another target that is attracting insects at your location. Comfrey is one of the flowers listed in that list of alternatives, just be sure to note that you have used this flower species if submitting a result. The sharp eyed might even not parasitic wasps and lacewings hanging around comfrey.

Distinguishing between common comfrey (symphytum officinale), hybrid comfrey and Russian comfrey is a task for experts. Fortunately pollinators are not always that discerning, any bushy stand of comfrey it seems will satisfy their needs.

For some pollinators the bell shaped flowers are a boon. This hardy perennial thrives in damp areas and for bumblebees with long tongues its lengthy flowering period (roughly May to August) is extremely helpful.  However, other bees are known to access it’s flowers. Dave Goulson’s writings on comfrey are always approving, and he notes “…one of the very best plants for bees. Visited by long and short-tongued species, the latter often robbing from holes bitten in the tops of the flowers.” 

Comfrey it seems is providing comfort and joy after all.

Further reading

Athayde’s blog on nectar robbing

Colourful parcels of poison 

By Athayde Tonhasca

For over 430 million years, plants and animals – particularly insects – have been entangled in an evolutionary tug of war. Through the inexorable process of natural selection, plants produce chemicals that deter or harm herbivores. These in turn develop the ability to overcome the plants’ defences, which in turn puts pressure on the plants to come up with ever more efficient chemicals. And so this arms race goes on.

As a consequence of these adaptations and counter-adaptations, plants have accumulated an arsenal of more than 300,000 catalogued products, known as secondary metabolites, which defend them against enemies. Among these chemicals, cyanogenic glucosides – CNglcs for short – are particularly efficient. When a plant-eating insect rips through plant tissue, CNglcs react with other chemicals to produce hydrogen cyanide, also known as prussic acid. This substance is highly poisonous to most animals (nearly twenty of Agatha Christie’s characters were dispatched with hydrogen cyanide or the related potassium cyanide). 

Cassava (Manihot esculenta) is a major source of calories for many people living in the tropics, particularly sub-Saharan Africa. The grated roots must be thoroughly washed to remove their cyanogenic glucosides © Thamizhpparithi Maari, Wikipedia Creative Commons

However, some millipedes, centipedes and insects have become immune to CNglcs. And in an ingenious twist of plant-herbivore coevolution, a few creatures have turned these poisons into phagostimulants (substances that induce eating).

Why would this happen? Through several behavioural and physiological adaptations, these herbivores have developed the ability to sequester CNglcs from their food plants, that is, ingest and store them in their bodies, without triggering the chemical reactions that create poisonous hydrogen cyanide. By accumulating CNglcs, these herbivores then put the toxic chemicals to work in their own defences against predators.

No insect illustrates this process of chemical manipulation better than burnet moths (Zygaena spp.), which sequester cyanogenic glucosides from the common bird’s-foot trefoil (Lotus corniculatus) and related food plant species (family Fabaceae).

Six-spot burnet moths (Zygaena filipendulae) taking nectar from a thistle © Lorne Gill/NatureScot

But that’s not all; burnet moth larvae can also produce their own CNglcs from amino acids taken from their host plant and store these chemicals in specialised cavities in their skin. When a larva is threatened by a predator, it contracts its body to expose the CNglcs viscous droplets.

CNglcs droplets on a six-spot burnet larva © Zagrobelny & Møller, 2011. Phytochemistry 72: 1585-1592

As a result of these chemical manipulations, caterpillars and adults are extremely unpalatable. Which explains why burnet moths fly about during the day: few predators would dare to take them. And these enemies are forewarned of the danger by the moths’ black-red contrasting colouration, which is a common pattern among poisonous animals.

But the six-spot burnet moth’s association with poison is even more remarkable. Females release gaseous plumes of hydrogen cyanide to attract males, and refuse to mate with those with a low content of CNglcs. If a male is suitably toxic and accepted, it transfers some of its own chemicals to the female during mating. It is believed that this ‘nuptial gift’ is relocated to her eggs to protect them against predators.

We don’t know much about burnet moth pollination, but in Britain they contribute to the reproduction of the fragrant orchid (Gymnadenia conopsea) and the pyramidal orchid (Anacamptis pyramidalis). 

A fragrant and a pyramidal orchid, both pollinated by burnet moths © Thommybe (L) and JLPC, Wikipedia Creative Commons

When life gives you lemons, you can make lemonade; but when life gives burnet moths cyanide, they make chemical weapons.

A sloppy but efficient pollinator

By Athayde Tonhasca

We hear a lot about the pollination services provided by the European honey bee (Apis mellifera), so you may be surprised to know this bee is not that competent at its job. A honey bee moistens the pollen she collects and carries it tightly packed on her corbicula, or pollen baskets, so pollen grains are not easily dislodged when the bee visits another flower. Moreover, honey bees learn quickly to collect nectar with minimal contact with the flower’s anthers, so reducing the chances of pollen transfer. They are also good at flower constancy (the trait of visiting the same type of flower over and over), which is not good for plants that need cross-pollination between different varieties, such as apples. Thus, paradoxically, honey bees’ efficiency as food collectors reduces their efficiency as pollinators. These shortcomings are offset by the huge numbers of bee workers per hive and the fact that they are so amenable to management.

In comparison with the tidy honey bee, the red mason bee (Osmia bicornis) is a messy flower visitor. Females have low flower constancy, flying all over the place, and carry dry pollen loosely attached to their scopa (a mass of hairs under the abdomen). This means that pollen grains have a greater chance of becoming detached from the bees’ bodies and ending up on a flower’s stigma.

A red mason bee with her scopa loaded with pollen © Jeremy Early, Nature Conservation Imaging

What’s more, the red mason is one the most polylectic bees in Europe, that is, it collects pollen from a variety of flowers from unrelated species: 18 plant families altogether, including willows (Salix spp.), maples (Acer spp.), birch (Betula spp.), oaks (Quercus spp.) and several fruit trees in the family Rosaceae such as apples, pears, plums, cherries and peaches. Unsurprisingly, this bee is an excellent orchard pollinator; 500 or so female red masons can pollinate as many trees as 2-4 honey bee colonies. 

Like other Osmia species, the red mason is a cavity-nesting bee; it makes itself at home in preexisting holes and fissures in soil banks or dead wood, abandoned insect burrows, hollow stems, or cracks and holes in walls – which explains the common name, ‘the mason bee’. It may also excavate soft mortar, hence the reason for another common name: ‘the mortar bee.’ The red mason readily occupies man-made structures such as ventilation bricks, the space beneath roof tiles, even inside door locks. So this bee is the most likely tenant of bee houses.

Once a female occupies a cavity, she will construct a series of compartments (brood cells) and stock them with pollen as food for her offspring. She will then close the nest entrance with a mud plug. But she’s not done once the nest is finished: if conditions are right, she may build another six nests before the season is over. The larvae will eat the pollen and emerge as adults the following year to start the cycle again. See red mason bees in action here.

A session of a mason bee nest. Each cell contains one egg and a provision of pollen 

Mason bees tend to nest close to each other in aggregations of 50 to 250 females. And they are diligent pollinators, as demonstrated by these facts and figures:

  • A female bee may construct 16 cells per nest, 1 cell/day.
  • She will fly 300-400 m on average, up to 600 m, in search of flowers.
  • Nineteen foraging trips are needed to collect the pollen and nectar for each cell.
  • Her pollen load weighs 100-250 mg, up to 300 mg.
  • She may visit 75 flowers each trip, up to 25 flowers/min, and she will stock up each cell in about 3.5 h.
  • A cell with an egg that will develop into a female bee may contain 8 million grains of pollen. Fewer for male bees (they need less food): 4.6 million.

This hardworking bee is good news for wild flowers, and also for crop production. The red mason is an effective pollinator of rapeseed oil and a number of crops grown under polytunnels and glasshouses, such as strawberries and raspberries. Other mason bees have been managed as orchard pollinators in Japan and USA for many years; there is growing evidence that the red mason can play a similar role in orchards in Britain and other European countries.

A female red mason bee and sealed nests in a bee house

The red mason bee is common throughout most of the UK from late March to June/July. During this short time as an imago (the adult stage), this bee will contribute to the pollination of countless wild flowers, crops and fruit trees. The red mason bee deserves to share the spotlight with the honey bee.     

Blaeberry bonus

The other day I enjoyed a trip to Glenfeshie, and it dawned on me that my outings to this favourite spot are changing.  Years ago a trip to Glenfeshie would inevitably have meant scaling Sgor Gaoith. However, lately I’ve become increasingly absorbed in exploring the glen itself. This time my visit was devoted, not entirely, but substantially, to contemplating blaeberry.

Now, blaeberry is one of those words you need to watch in spell-checker. Microsoft Word is determined to tell me that I actually want to say blueberry. I don’t.  But then again the software has my sympathy, for surely no plant owns quite so many names. The list is impressive, and includes bilberry, huckleberry, wimberry, trackleberry, and whorlberry.

Vaccinium myrtillus, to avoid confusion, is widespread in our Caledonian Forests, but not exclusively so. You can also find it on moors, heaths and bogs. When it flowers in May this evergreen shrub is a magnet for bumble bees and other pollinators, and if you want to spy the elusive bilberry or blaeberry bumble bee (Bombus monticola) then this is a plant worth watching.

Bombus monticola (monticola translates from Latin as ‘living amongst mountain’) isn’t the only bumble bee to forage on this straggly deciduous shrub. However, it is thought that they are fairly heavily dependent on this particular plant, probably because in truth there is little else available at this time of year. In Glenfeshie, where the pressure of grazing has been substantially reduced monticola has a fighting chance with blaeberry. 

That said the blaeberry bumble bee will forage on the mountain tops, and for me it was whilst looking for dotterel and ptarmigan that I realised this plucky bee was covering the summits as well as the glens.

The blaeberry plant is, like the bumblebee, as attractive as they come.  The light green leaves have blushing fringe of pink, and the deep pink flowers hang like exotic miniature lanterns. When it fruits the dark blue-black berries are bold against green or reddening leaves.

It is one of our edible wild fruits and is used in jams and jellies as well as having been pressed into service to temper rougher, harsher whisky. The human uses of blaeberry don’t end there and the blue-black berries were once a go to source of dye when clothing needed a bit of colour.  Such practical uses earned it a special place in the hearts and minds of many.

Nan Shepherd in her magnificent The Living Mountain talks about blaeberries in the same glowing terms as the arguably tastier cloudberries.

So what to make of blaeberry? Understated yet beautiful.  Food for the blaeberry bumblebee, butterflies such as the mountain ringlet, and small mammals including the red squirrel. A source of relish and dye for our forefathers.  Important for the chicks of ptarmigan, grouse and capercaillie. And for me? A plant that can easily distract you from the mountain tops.

Futher reading:

The blaeberry bumble bee, the hardy highlander

Bumblebee Conservation Trust – The Bilberry Bumblebee

Great minds think alike

Scotland’s Community Groups do so much for our pollinators.  In mid-June we will host a conference to celebrate their many pollinator-friendly actions, but for now let’s take a closer look at two fantastic community actions. Whether you visit Starbank Park in the capital city, or chat with Broughty Ferry’s Margaret Alston your appreciation of all things pollinator is bound to grow.

You probably think Jam, Jute and Journalism when it comes to considering the great successes of Dundee. But three ladies in Broughty Ferry have been working hard to add a new category to celebrate – bumblebees!  A few weekends ago Mag and Lil, whom many of you will know if you follow their twitter feed, and seek out Dundee-based bumble bee news, were pushing their pollinator friendly advice at Dundee University Botanic Gardens.

Mag (better known to some as Margaret Alston) is an energetic retired Primary School teacher, and teaching is the chosen profession of her daughter Holly too. Mag’s grand-daughter Lil is the youngest member of the dynamic trio. However, regardless of which generation you speak to, the love of pollinators, and especially bumblebees, shines through.

In what their first face-to-face event since lockdown, the emphasis at Dundee’s Botanic Gardens was on bumblebee fun and garden activities for all the family. Their Children’s Activity Stall was ‘buzzing’ with energy and we were delighted to provide them with our range of Children’s Activity sheets for the day – featuring bumblebees, solitary bees and honey bees.

Mag and Lil welcome children and their adults of all ages to their activity sessions, and promote a simple message … bumblebees (and other bees) need our help!

The focus their events is on the basic needs of all living creatures, explains Margaret “We focus on flowers as they are the bumblebee’s source of food, water and shelter. It’s so important to emphasise the need of safe places to make nests and hibernate. There is also an acknowledgement that we in turn benefit when bumblebees pollinate our food crops and other flowers….they make our world a better place to be(e).”

Their fun filled activities reflect this message, and their hope is that children and adults leave the stall having learnt something about bees and with a renewed determination to help them. Those activities are many and varied and include making miniature gardens where bumblebees might like to live, a quiz (everyone loves a quiz!), a game called hook a bumble. And there are prizes.

Don’t worry if you didn’t make it along in May, come June 11th you have another chance to be enthused by this marvellous trio as they will be bringing their brand of bumblebee magic to an event in Broughty Ferry. Watch their twitter feed for further information.

Margaret’s philosophy is grounded in solid common sense and years of experience as a teacher. “When dealing with very small children,” she explains, “a story or a bit of drama compounds learning in a very effective and unforgettable way. At our event in the Broughty Ferry library I shall be doing a little bit of play acting encouraging children to join in, with a giant flower and a little bumblebee! Holly or Lily will be reading ‘I Saw a Bee’ by Rob Ramsden (it gives a brilliant message about bees to tiny children) and there are some lovely worksheets and teachers pack to go with the book.”

Head south across the Firths of Tay and Forth and you might, if you are lucky, find yourself at Starbank Park. Here Janet McArthur, Chair of the Friends of Starbank Park, inspires a willing army of volunteers to do their bit for pollinators.

In a well thought through pollinator-friendly approach everything from diverse floral planting schemes, to the inclusion of flowering trees and bee hotels is catered for.

The enthusiastic Friends of Starbank Park has this year focusing on native plants and – given the circumstances in Ukraine since February – sunflowers.   Indeed the group has been packaging up hundreds of sunflower seeds as part of a local fund-raising effort which have been sold in shops and cafes in their local community raising to date just under £500. There is an affinity for sunflowers at Starbank, last year saw volunteers, including local nursery schools, plant hundreds of sunflower seeds.

A visit from the Duke and Duchess of Cambridge coincided with an event to scatter pollinator friendly seeds in the park last year. That royal connection helped the Starbank Group’s pollinator planting area enjoy being published in the media throughout the UK, highlighting the need for more pollinator friendly patches.

Serious thought is given to what is planted.  The group leaves plants such as loosestrife in the hedge to help orange tip caterpillars feed, and packs their flower beds with cosmos, nasturtiums, foxgloves, scabious, oxeye daisy, and lupins giving an aesthetically beautiful garden centrepiece that is a feast for pollinators.  

Forward thinking is often the key to success, and the group ably demonstrated this in collecting the seeds of their many pollinator friendly flowers in order to plan sowing the following season’s flowers. 

Add to the mix the fact that Starbank Park run workshops to promote bees and butterflies in their local community and planted hundreds of crocus bulbs last autumn to feed the bumblebees early spring it is clear that planning is a key strength of Janet and her team’s outlook.

So be it Broughty Ferry or Starbank Park you can be sure to that pollinators are being considered, and then some.

Join the NatureScot Community Groups conference:

Last year NatureScot hosted an online conference looking at the relationship between pollinators’ needs and Local Authorities greenspace actions.  This year the conference — on the morning of June 21 — will focus on Community Groups. The aim is to celebrate pollinator-friendly approaches, share good practice and offer advice on how to get your community involved. Speakers will include Athayde Tonhasca, Scott Shanks, Paul Castle, Catherine Lawson, Leigh Biagi and Francesca Martelli.  To attend please contact

Follow the Mag and Lil twitter feed

A feathery pollinator

By Athayde Tonhasca

As gardeners across the country gradually come out of hibernation to resume tending their flower pots and vegetable beds, they can count on one visitor for company: the Eurasian blue tit (Cyanistes caeruleus). This little bird is a common sight all year round in gardens across the UK, and it is definitely good company because it spends a good chunk of its time hunting leaf-munching caterpillars – although flies, aphids, beetles, wasps and spiders would also do for lunch. Outside the breeding season, they also eat seeds and buds.

The Eurasian blue tit © Francis Franklin, Wikipedia Creative Commons

This everyday bird and the related great tit (Parus major) came into the spotlight in 1921 when they were found to be behind cases of pilfering from British residences. These birds had learnt to prise open or pierce the foil tops of milk bottles left at people’s doorsteps to get at the layer of cream underneath. And they became really good at it: “The bottles are usually attacked within a few minutes of being left at the door. There are even several reports of parties of tits following the milkman’s cart down the street and removing the tops from bottles in the cart whilst the milkman is delivering milk to the houses.” (Fisher & Hinde 1949, The opening of milk bottles by birds. British Birds 42: 347-357). The technique spread quickly, and by 1947 several places across the UK were recording bottle-opening tits. The birds’ cleverness became a case study in social learning.

Tits having their breakfast © Fisher & Hinde, 1949. British Birds 42: 347-357

The blue tit is also known for its acrobatics: when searching for food, it can cling to walls, hold on to the narrowest twig and hang upside down to explore holes and crevices. The talent for gymnastics offered the blue tit a new opportunity – a boost of energy from flowers of the crown imperial fritillary (Fritillaria imperialis).

This plant from the lily family (Liliaceae) is native to Asia and valued by European and American gardeners for its clusters of bell-shaped flowers. In the UK, these flowers are visited by bumble bees, which are attracted by abundant nectar. Birds may be enticed as well, although most of them have to cut through the top of the flowers to get to the nectar. But not the blue tit: it has the right size and skill to access the flower through its opening, without damaging it.

Crown imperial fritillary or Kaiser’s crown © James Steakley, Wikipedia Creative Commons

Nectar feeding is rare among European birds: in fact, not one species is considered to be a specialised nectarivore. But the blue tit is known for dabbling in nectar now and then from plants like gooseberry (Ribes uva-crispa) and willows (Salix spp.). Different from most passerine birds, blue tits seem to be able to digest sucrose, a quirk that is likely to give them an advantage over great tits, their garden competitors. 

To the crown imperial fritillary, visits by inquisitive blue tits are most welcome. While probing a flower for nectar, the bird touches anthers and stigma, and when it hops to another flower, inevitably pollen is transferred. So, as a first for a plant growing in Europe, the crown imperial fritillary is mainly – or perhaps solely – pollinated by a bird. 

Blue tits visiting crown imperial flowers © Búrquez, 1989. Oikos 55: 335-340

In Europe, 46 or so bird species visit flowers, and it is usually assumed they are looking for insects or other invertebrates. But most of these birds are generalists, feeding on whatever comes to hand. So it’s possible that some of them occasionally go for a sip of nectar, just like the blue tit. And just like the blue tit, a few birds may contribute to pollination. Of the nearly 100 European plants visited by birds, about a third are introduced species like the crown imperial fritillary. If some of them are pollinated by native birds that take advantage of a novel food source, the ecological implications may be profound. We won’t know until the matter is investigated. Who knows, perhaps some bird besides the blue tit will join insects on the list of British pollinators.

Forvie feast

To visit Forvie National Nature Reserve at this time of year is to enjoy a flowery treat.  And, of course, where there are flowers it follows that you are likely to see a range of pollinators too.  That’s certainly the case at Forvie and the insects are quick to recognise a feast when they see one.

The reserve came into being in January 1959, covers almost 1,000 hectares of sand dunes, heathland and the Ythan estuary. It is an area that has long been a research spot for Aberdeen University and the food webs present here are amongst the most studied in the world. Home to a rich variety of wildlife, seals and birds are the biggest magnet alongside the vast sand dunes which evoke images of far flung deserts. Breaking waves, gusting winds, terns and eiders can deliver an ever-changing acoustic backdrop

The Sand Loch and Dune Trails are understandably popular, but if its pollinators you seek then the two-mile Heath Trail is probably your best bet. It’s an easy path with a gravel surface and occasional grassy sections – although it is worth noting that this is the great outdoors so uneven surfaces and one or two muddy patches are possible.

Catriona Reid is the energetic reserve manager at this rolling site, a dozen miles or so north of Aberdeen, where over 350 species of plant have been recorded.  

“At the moment we have bursts of red campion and the coastal delight of thrift,” she recently told me. “My favourite quirky fact about thrift is that it featured on the reverse of old thruppenny bits. We’ve also got creeping willow catkins at Hackley Bay (and they are lying all over the moor here just now), cuckoo flower, common vetch, meadow saxifrage, violet and the rather unappealingly named lousewort.  The cliffs are currently covered in primulas – great swathes of primroses and false oxlips.

“That’s not a bad range.  On my regular walks round the reserve I enjoy seeing many insects and just now a favourite are the small tortoiseshells, tussling in the sunshine. I’m always hoping to see something new, too, I keep looking for orange-tip butterflies on the cuckoo flower – but I’ve never yet seen one here at Forvie.” 

A good place to find out about the host of wild flowers on the reserve is in the Forvie blog . It’s worth checking out for regular and appealing pictures of flowers which are arguably at their best in May and June.  

A look at the NBN gateway reveals that red-tailed bumblebees are often seen here (and I can vouch for that). The red-tailed is one of our ‘it does what it says on the tin’ bumblebees, probably our easiest to identify with the red tail being the only non-black area on the females. One of the so-called ‘big seven’, it has been identified in each and every county of Scotland.

Amongst the other Forvie bumblebees common carders are regularly reported. The common carder is interesting for its appearance too. Known in some quarters as ‘the dusty miller’ or ‘baker bee’, its colouration is a nod to the flour-spattered, dusty looking, brown coats which bakers used to wear. Unlike most bumblebees it doesn’t boast a bold stripey appearance which is a warning to many would-be predators, but the common carder seems to manage just fine without the vivid black and yellow colouration. 

When it comes to butterflies, however, the most oft recorded species at Forvie, by some distance, is the small tortoiseshell, probably because they are colourful and very obvious. Nevertheless, the Forvie butterfly stars are surely the striking fritillaries – small pearl-bordered and dark green – which are well worth patiently seeking out. And some years produce impressive mass influxes of painted ladies, migrating, over several generations, from North Africa.

The reserve has a relaxing semi-permanent wildflower zone near to the equally welcoming visitor centre. In the centre you will find a series of displays, a film presentation and tactile exhibits about Forvie. Some of the information reflects the fact that the area has associations with fishing and this is subtly reflected on the Heath Trail where the interpretation panels sit on upturned recycled wooden ‘fish crates’.

Forvie can be a challenging environment for bumblebees and other eager pollinators. Catriona says “Sometimes strong wind grounds the bumblers – we kept finding them on the path the other day – but when we very gently nudged them, it was clear they were ok, they just didn’t want to fly. I can’t say I blame them!”.  Then again they might simply be taking a break from feasting.

Further reading:

Pollinators at Forve blog 2021

A bitter-sweet medication

By Athayde Tonhasca

Most flowering plants need to keep pollinators happy. If not, the flow of pollen from flower to flower is interrupted or reduced, which will impair or prevent plant fertilization. To avoid such a disaster, many plants entice flower visitors with an irresistible reward: nectar. This solution contains 15% to 75% (by weight) of sugars – mostly glucose, fructose and sucrose – free amino acids, proteins, minerals and lipids. Bees, wasps, hover flies, mosquitoes, butterflies, moths, hummingbirds and bats are among the most enthusiastic consumers of this energy-packed drink. Not all nectar-eaters are pollinators, but nectar pilfering is a price plants have to pay to get pollinated.

A hummingbird hawk moth (Macroglossum stellatarum) taking a sip of nectar © Charles J. Sharp, Wikipedia Creative Commons

But nectar is more than nutrients dissolved in water. It contains a variety of secondary metabolites (compounds that are not directly involved in an organism’s development) such as tannins, phenols, alkaloids, flavonoids and terpenoids. The role of these chemicals are not completely understood. Some of them are indigestible, unpleasant (too bitter) or toxic to animals, so they defend plants against plant eaters, pollinators included: bees and other insects can be poisoned by secondary metabolites in nectar and pollen. But some nectar-diluted chemicals have positive effects: caffeine enhances pollinators’ memory, while other substances act as addictive stimulants, attracting insects or inducing them to stay around for longer, thus increasing the chances of pollination. 

These metabolites play another part in plant’s lives, one which importance is being increasingly recognized: as antimicrobial agents. The evening trumpet flower or yellow jessamine (Gelsemium sempervirens) provides a nice example of nectar’s medicinal qualities.

This garden plant, native to warmer parts of the Americas, is loaded with the alkaloid gelsemine. This strychnine-related chemical makes the whole plant toxic to humans, livestock and to honey bees. Bumble bees however not only are immune to it, but they also get some protection against Crithidia bombi, a widespread gut parasite that reduces the development and survival of colonies. Gelsemine-laced nectar may lower the rate of C. bombi infection by 65%.

The evening trumpet flower © Kenpei, Wikipedia Creative Commons

Gelsemine is not the only natural prophylactic against C. bombi. Callunene, found in the nectar of common heather (Calluna vulgaris), reduces the parasite’s infectivity against the buff-tailed bumble bee (Bombus terrestris), and in this case we know how. Crithidia bombi is a flagellated protozoan, that is, a single cell organism with a whip-like appendage called a flagellum. Callunene induces the loss of the flagellum, which the parasite uses to attach itself to the bumble bee gut.   

Crithidia bombi © R. Schmid-Hempel, ETH Zurich

Heather, together with white clover (Trifolium repens), marsh thistle (Cirsium palustre), and bell heather (Erica cinerea), are responsible for about 50% of all the nectar produced by flowering plants in the United Kingdom. We can only imagine the protective effect of heather on bumble bee populations. As virtually all plans secrete some secondary metabolites with their nectar, certainly there is much more to be discovered about their medicinal properties and consequences for pollination services.

A field of common heather, bumble bees’ pharmacy © Rasbak, Wikipedia Creative Commons

A greater understanding of nectar pharmacology may benefit us directly. Various alkaloid, terpenoid and phenolic compounds are lethal to other protozoans related to C. bombi (family Trypanosomatidae). Some of these trypanosomatids are responsible for awful diseases, like Trypanosoma brucei, which causes human sleeping sickness, and T. cruzi, the agent of Chagas disease. So, who knows: a healthy bumble bee may be a clue for reducing human suffering.