Refuge for Butterflies in Stirling’s Green Spaces

Natasha Allen, recent graduate from the University of Stirling and aspiring Ecologist, is our latest guest blogger. For her MSc Dissertation, she set out to determine if a reduced mowing regime and wildflower seed mix sowing were helping to produce more favourable habitat for butterflies in Stirling green spaces.

“Meadows and other species-rich grasslands are key habitats for UK pollinators. Consequently, the destruction of over 97% of UK meadows since the 1930s has brought about hard times for our pollinating invertebrates. Butterfly Conservation’s recent publication of the State of UK’s Butterflies 2022 indicates an eye-watering 80% of UK butterfly species have declined since the 1970s.

There is no denying the cultural significance of the charismatic butterfly; their beauty has forever inspired us. But there is so much more to butterflies to get excited about: these deceptively sturdy invertebrates are useful indicators of environmental health and the impacts of climatic change, due to their sensitivity to temperature, relatively high mobility, and short lifecycles. Not to mention they play vital ecological roles across different ecosystems!

One of the wildflower-sown pollinator sites in late July. The strip of short-cut grass demonstrates the difference in vegetation structure between the two management regimes.

With encouragement and guidance from organisations such as Butterfly Conservation Scotland and local community project On the Verge, Stirling Council has set aside sections of amenity grassland (grass frequently cut short for recreational use) in towns across the county to trial run a more pollinator-sympathetic management regime. Since 2021, these areas have been mown once annually with cuttings collected (Regular Pollinator or RP sites). But prior to this trial run’s establishment (between 2011-2015), the composition of vegetation at 3 different amenity grasslands in Stirling were directly altered using wildflower seed mixes and have since been treated with the same annual cut-and-collect method (Wildflower Pollinator or WP sites).

For my dissertation project with the University of Stirling, we carried out survey work across all three management types to compare the impacts of each regime on plant and butterfly diversity.

Map of the Stirling area, indicating the 6 locations of the 12 surveyed sites.

Twelve sites were surveyed in total: 3 WP sites, 3 RP sites and 6 amenity grassland sites situated adjacent to each of the 6 pollinator-sympathetic regime sites. 

• Observations of butterflies were recorded as the surveyor walked along fixed zigzag transects within each of the 12 sites. These surveys were carried out at least once a week (when the weather permitted it) from mid-June to late July 2022.
• To assess the plant diversity at each site, two vegetation surveys were conducted during this period, to assess the frequency of all plant species within each butterfly walk transect. 
• Over 7 weeks, 10 replications of butterfly surveys were performed, providing data from 460 butterfly transect walks. 

In total, 8 butterfly species were recorded over the course of the study: Meadow Brown, Ringlet, Small White, Green-veined White, Common Blue, Small Copper, Small Tortoiseshell and Peacock. Rather unsurprisingly, Meadow Brown and Ringlet butterflies were the most abundant, together making up 81.4% of all the butterflies we observed. 

Table showing the summary of results from our survey work.

During fieldwork, it was evident that both pollinator-sympathetic regimes supported much greater butterfly diversity than the amenity grasslands could. Our results indicated a 36% chance of seeing a butterfly at both RP and WP sites, compared to 1% on amenity grassland sites. Out of the 86 individuals observed during the survey work, only 3 butterflies (2 Meadow Browns and a Ringlet) were ever recorded on the amenity grassland sites. 

As expected, the WP sites had the highest count of plant species. Yellow Rattle, Creeping Thistle, Ox-eye Daisy, Meadow Vetchling, Common Bird’s-Foot Trefoil and Meadow Buttercup were among the many forb species sprinkling colour amongst the grasses of the WP sites. It will take longer for plant diversity to improve on RP sites, as the simple cut-and-collect regime relies solely on the long-term removal of cuttings to decrease nutrient levels in the soil, so that less competitive species can thrive. 

Despite the relatively similar vegetation composition between the RP and amenity grassland sites, butterflies clearly favoured one over the other. The simple act of reducing mowing frequency down to once annually (allowing vegetation to grow tall) clearly increased the probability of butterflies being present. Not only does letting the vegetation grow taller provide more floral food resources for adult butterflies, it also provides vital shelter and temperature regulation for butterflies. For species such as the Meadow Brown or Ringlet, long grasses play an integral role in their lifecycle, providing food during the larval stage of their development. Other animals such as birds, bats and hedgehogs, feed on butterfly caterpillars. So, by letting the grass grow tall, these green spaces can better support insect larvae and, in turn, the wider ecosystem.

Photograph of female Common Blue butterfly at the Newton Park pollinator trial site, Dunblane.

Both management regimes have their place in pollinator conservation. Simply limiting cutting to once annually is easily implemented and the removal of cuttings year after year will gradually promote further plant diversity. Sowing wildflowers can be utilised to provide wonderful opportunities for public engagement and education, which is necessary if we want to shift public attitudes towards biodiversity-favourable green space management. It can also be harnessed to support target pollinator species. In the case of Newton Park in Dunblane where Common Blue butterflies were observed, the population of Common Bird’s-Foot Trefoil (the butterfly’s primary larval foodplant) is currently minimal. On the Verge are in the midst of establishing a plot of wildflower sown grassland at Newton Park. With the inclusion of this Trefoil in the native wildflower seed-mix used, On the Verge’s important community work could help sustain the Common Blue at Newton Park for years to come.

Diversity of habitat is key if we are to encompass the needs of a broad range of butterfly species and other pollinator taxa in our management of town and city green spaces. Alongside our efforts to increase the pollinator-sympathetic management of our agricultural land, mosaics of long grass and wildflower meadows within our urban parks and roadside verges should be maintained to provide further refuge for butterflies.

With thanks to Anthony McCluskey of Butterfly Conservation Scotland (Engagement Officer), Leigh Biagi of On the Verge (Stirling), Guy Harewood (Biodiversity Officer for Stirling Council) and Dr Joanne Clarke (Lecturer in Biological and Environmental Sciences at the University of Stirling).“

Images all (c) and courtesy of Natasha Allen

A hard flower to crack

By Athayde Tonhasca

Brazil nuts are high up in the list of superfoods, a gimmicky but highly profitable market. For some internet gurus, the nuts protect you against inflammation, heart disease, diabetes and cancer; and, inescapably as superfoods go, they are loaded with ‘antioxidants that fight free radicals’ – a scientifically baseless but commercially catchy label. Hype aside, Brazil nuts are highly nutritious: they are loaded with proteins, carbohydrates, unsaturated lipids, vitamins and essential minerals such as calcium, magnesium, phosphorus and potassium. But their main claim to fame is to be one of the best sources of selenium, an essential element for a range of metabolic processes in our bodies. These nuts have their detractors because of the unlikely risk of selenium poisoning for those who over-indulge in them, and the danger posed by aflatoxins (carcinogens produced by certain fungi) when the nuts are not stored properly. The healthy aspects of Brazil nuts are clearly winning over the popular perception because the European and American markets keep growing steadily. Which is good news for the main nut producers Bolivia (the world’s major exporter), Brazil and Peru.

Assorted nuts, essential while watching a match on the telly © Melchoir, Wikimedia Commons.

The nuts are in fact seeds extracted from the hard, coconut-like fruits produced by the Brazil nut tree (Bertholletia excelsa). Named excelsa (high, exalted, lofty) by naturalists and explorers Alexander von Humboldt and Aimé Bonpland, this is one of the tallest trees in the Amazon region. Some individuals reach heights of 30 to 50 m, with trunks of 1 to 2 m in diameter – up to 5 m in older specimens. And they can live long lives: radiocarbon dating has identified some 800- and 1000-year-old trees (Camargo et al., 1994).

Brazil nuts are gathered from fruits fallen to the forest floor during the rainy season. The work, carried out by native people and small farmers, has one serious risk: the thick-walled fruit of the Brazil nut tree is 10-15 cm in diameter and weighs on average 750 g. A fruit of this size falling from about 7 m generates sufficient kinetic energy to fracture a skull and cause severe to fatal injuries (Ideta et al., 2021).

A Brazil nut fruit and seeds in their shells, and seeds ready for the market © P.S. Sena and Quadell, Wikimedia Commons.

Brazil nuts are harvested almost entirely from wild trees because tree cultivation has been largely unsuccessful. One of the reasons for the failure to turn the tree into a farm commodity is its pollination requirements.

The Brazil nut tree reproduces by cross-fertilisation, but its flower is not the run-of-the-mill, pollinator-friendly structure found in most plants. It has a curled extension – called a ligule – that forms a hood over the petals, which are pressed together like an inverted cup. Ligule and petals create a chamber that conceals stamens, stigma, and the nectaries. To access the nectar, an insect has to squeeze itself between the ligule and the tightly packed petals. If successful, the visitor may come out dusted with pollen and transfer it to another flower.

The inflorescence of a Brazil nut tree © Scott Mori, The New York Botanical Garden, Lecythidaceae – the Brazil nut family.

The flowers of the Brazil nut tree receive many visitors, including hummingbirds, moths, butterflies, beetles, and several bees. But getting into a flower for its nectar is not for the nimble or weak; only the largest and strongest bees can lift the ligule to reach the reproductive organs.  This select heavy-weight club includes bumble bees (Bombus spp.), Centris spp., Epicharis spp., orchid bees (Eulaema spp.), and carpenter bees (Xylocopa spp.). 

An E. meriana orchid bee (L) and a large carpenter bee (X. mexicanorum), two of the robust bees capable of handling a Brazil nut tree flower © Insects Unlocked, Wikimedia Commons.

In the central Amazon rainforest, the orchid bee E. mocsaryi and carpenter bee X. frontalis are especially important Brazil nut tree pollinators because of their abundance and frequency of flower visitations (Cavalcante et al., 2012). Watch X. frontalis hard at work. 

An E. mocsaryi orchid bee forces itself between the ligule and the tightly packed petals of flower of the Brazil nut tree © Cavalcante et al., Wikimedia Commons.

The large bees that pollinate the Brazil nut tree can fly long distances, which is important for maintaining its genetic diversity: trees typically grow in groups of individuals that are isolated from each other in the forest. These bees are solitary or semi-social, and none of them have been domesticated; so their survival depends on the natural habitats that supply nesting sites, food – one type of tree alone will not provide for the whole season – and other resources such as orchid fragrances, which are collected by male orchid bees.  

Other characters play an important part in the life of a Brazil nut tree: rodents. The fruit capsule is too hard for most animals that could be interested in the nutritious seeds – but not to agoutis (Dasyprocta spp.). Thanks to their powerful teeth, they can gnaw their way to the seeds. Sometimes an agouti can’t eat all the seeds at once, so the prudent animal takes them some distance away (up to 20 m) and buries them as a food reserve for leaner times. But it so happens that the agouti’s memory is not the sharpest; it often forgets the way back to the food cache. Or the agouti itself may become a meal for a large cat before returning to its seeds. Either way, the buried seeds germinate. This unintentional planting by agoutis, pacas (Cuniculus spp.) and the southern Amazon red squirrel (Sciurus spadiceus) is the only route to seed dispersal for the Brazil nut tree, thus is vital for its survival. Follow the exploits of a forgetful agouti in the forest.

A red-rumped agouti (Dasyprocta leporina) © Alastair Rae, Wikimedia Commons.

As one can imagine, these required interactions with bees and rodents don’t bode well for the future of the Brazilian nut tree. Amazonian ecosystems have been eroded away by the relentless march of deforestation and land conversion to agriculture and pastures. To make things worse for the tree, its wood is highly valuable (its felling is illegal, but that doesn’t stop illegal loggers). One of the consequences of the devastation is the increasing scarcity of Brazil nuts in Brazil, which helps explain why Bolivia took the lead as the main exporter. 

We may take the hard-nosed view that we can’t do anything about the plight of the Brazil nut tree, but that’s not quite right. One could be inquisitive and demanding about the origin of a nice piece of hardwood furniture for sale, or the juicy steak in a restaurant or supermarket freezer (much of exported South American beef comes from deforested areas). Or we could accept a life without Brazil nuts: after all, to us they are just comfort food. But the tree’s demise could be a portent. In the 1980s, doomsday prophet Paul Ehrlich and his wife Anne Ehrlich famously compared species’ roles in an ecosystem to rivets in an aeroplane’s wing. Aircraft manufacturers use more rivets than necessary to affix the wings, so removing a few of them would make little difference. But if they continue to be taken away, at some point a critical rivet is lost, and the aeroplane will crash. Similarly, how many species can you lose before an ecosystem fails? We don’t have an answer for that, or even know whether the Ehrlichs’ model is realistic. The eventual loss of the Brazil nut tree could be just one redundant rivet popped out of the body of biodiversity; or it could be a warning of bad things to come to bees, agoutis, the forest and its peoples, and, at the end of the queue, to us, sophisticated Brazil nut munchers. 

The Brazil nut tree is the symbol of the Amazon Forest. Its size makes it difficult to capture it whole in a photo © upper left: My Favorite Pet Sitter; lower left: mauroguanandi; rigth: Edsongrandisoli, Wikimedia Commons.

A rattling good tale

When it comes to creating a meadow you need allies, and they don’t come much more reliable than yellow rattle.  Rhinanthus minor, to roll out the scientific name, is one of those plants, like kidney vetch, red clover and common knapweed, which is a staple of meadows and an absolute boon for pollinators. And in the case of yellow rattle’s its value extends beyond nectar and pollen.

Now if I told you yellow rattle is a parasite you might recoil, but you should resist; not all parasites are bad news.  Yellow rattle is a point in case.

Yellow rattle is what botanists refer to as a hemiparasitic plant. The ‘charge’ laid at its door is that it steals nutrients from surrounding grass roots. How does it do this?  It can send out roots of its own which in turn invade the roots of neighbouring grasses, hence the occasional reference to ‘vampire’ behaviour. As you can imagine this isn’t great for those unsuspecting grasses which will, as a result, experience a loss in height and vigour. 

With the advantage switched from grasses to yellow rattle, other less dominant wildflowers seize the moment and move in to exploit the emerging opportunity. It’s this ability to help encourage floral diversity which earns yellow rattle the charming nickname of the ‘meadow maker’.  

Greater Yellow-rattle (Rhinanthus angustifolius) growing on the Battleby meadow

That’s a name they would approve of in the environment team at East Dunbartonshire Council.  They have increasingly sown yellow rattle in early autumn on areas they have carefully scarified.  This is followed up with both the seeds of other species and the direct planting of tiny plants of different species.  The yellow ‘meadow magician’ is however is the star ingredient within the floral recipe. A key point in the years thereafter is making sure that mowing is planned for late summer, carefully timed to take place after the yellow rattle and wildflower plants have shed their seeds.

Relaxed mowing regimes and delayed cuts fit neatly with another East Dunbartonshire Council tactic. They’ve identified a reduction in the rotations for grass-cutting as an intervention which they can easily follow, whilst simultaneously gaining biodiversity benefits. Ever adaptable, when the council found they simply couldn’t resource creating any new perennial meadows in 2022 they compensated by sowing annual pictorial flower meadows on roundabouts and along transport corridors whilst protecting ongoing perennial meadow management. This entailed adopting a welcome cut-and-bale strategy for all of their meadow sites. The introduction of soft-track machinery on the wettest areas was another welcome advance, both for the soil structure and aesthetically.

That’s our mechanical cue to return to ‘nature’s lawnmower’, yellow rattle.

Yellow rattle (Rhinanthus minor) seedhead

Yellow rattle is an intriguing name. Why ‘rattle’ you might ask? The answer is remarkably logical, for when it sets seed it makes the sound of a rattle when your brush against the seed pods. Indeed few plants have such a range of fascinating descriptive names. Penny rattle, rattle basket, hay rattle and rattle grass are all ancient local names that capture the essence of the sound those dry seed pods make. In some areas the pods themselves were known as dog’s pennies as they resembled rough coins and formed part of childhood games. 

In Gaelic the common name for yellow rattle is bodach nan claigeann, literally ‘old man of the skulls’. It is also referred to as gleadhran ‘rattling one’ and modhalan buidhe ‘yellow humble one’.

There are many delights with yellow rattle and they aren’t confined to the list of charming names. It holds its nectar quite deep and is thus popular amongst long-tongued bumblebees. Fascinating studies have revealed that yellow rattle is also susceptible to nectar robbing where shorter-tongued bumblebees simply gnaw through the flower to cleverly reach the otherwise unobtainable nectar supply.

What more could you want when it comes to plant gazing? What with ‘vampires’, ‘magicians’ and ‘nectar robbing’ that’s surely more intrigue than most plants offer.  

The best time to see yellow rattle in Scotland is between May and July.

The itsy bitsy influencers

By Athayde Tonhasca

Arachne, born in the ancient kingdom of Lydia, was really good at weaving. A masterful weaver perhaps, but not wise. She boasted about her skills to the world, claiming she was better than Athena herself, the goddess of handicrafts. All that braggadocio reached heavenly ears, and the offended goddess thought it was time to take down the impertinent Lydian a peg or two. Disguised as an old woman, Athena appeared before Arachne and warned her that stirring up the gods could end in tears. Arachne not only ignored the old biddy’s advice but challenged her to a weaving contest. Athena revealed her true identity and shrieked back: “you’re on, witch!” (or words to that effect; translations vary). Proving beyond doubt she wasn’t wise, Arachne didn’t back down. Worse: she created a superb piece, but of tabloid content. Her tapestry depicted the unconventional liaison between a swan (Zeus in disguise) and Princess Leda, and Zeus cross-dressed as a satyr and as an eagle during other dalliances. She also wove various romantic transgressions by members of the royal family such as Apollo, Dionysus and Poseidon. 

Despite admitting defeat to the better weaver, Athena was incensed and humiliated – after all, Zeus was her daddy. She tore Arachne’s work to pieces and destroyed her loom. For Arachne, the drachma finally dropped. Horrified by her recklessness, she hanged herself. Athena, who was also the goddess of wisdom, decided that the silly mortal had learned her lesson. She turned the hanging rope into a cobweb and brought Arachne back to life, but not as before. In Metamorphoses, Book VI, Ovid tells us what happened (translated by A. S. Kline): “Arachne’s hair fell out. With it went her nose and ears, her head shrank to the smallest size, and her whole body became tiny. Her slender fingers stuck to her sides as legs, the rest is belly, from which she still spins a thread, and, as a spider [arachni in Greek], weaves her ancient web.” Hereafter, Arachne’s descendants would hang from threads and carry on as skilled weavers.

Minerva (the Roman version of Athena) cancelling Arachne for her hate speech against the gods. Art by René-Antoine Houasse, 1706. Wikimedia Commons.

Arachne’s chronicle is one of the many myths, legends and symbolisms involving spiders (Class Arachnida, Order Araneae) in Western cultures. Despite their relevance in the humanities, spiders tend to provoke a range of negative emotions in people: fear, revulsion, loathing. Indeed, children of school age fear spiders the most, ahead of being kidnapped, predators or the dark (Muris et al., 1997); the American Psychiatric Association recognises arachnophobia, the persistent and irrational fright caused by spiders, as a mental disorder that afflicts a number of people. The innate fear of spiders and snakes is likely to be a remnant behaviour acquired during our evolutionary history for identifying and avoiding animals that could be harmful to us (e.g., New & German, 2015).

Helping children to sleep peacefully: Little Miss Muffet is about to make an acquaintance. Art by Arthur Rackham, 1913. Wikimedia Commons.

Spiders’ negative image is not helped by misinformation: Mammola et al. (2022) amassed data from newspapers in 40 languages around the world and concluded that about half of the news were erroneous, misleading or sensationalist. This is deeply regrettable, as spider incidents involving humans or domestic animals are exceedingly rare, especially considering how abundant they are: you could bump into 130 to 150 individuals/m² in some habitats. But you are not likely to see most of them because they are small, nocturnal or hunt among the soil debris. The 45,000 or so known spider species are spread throughout practically every terrestrial habitat in the planet. Instead of biting people, spiders spend most of their time stalking or chasing unsuspecting prey (except for one herbivorous species, the wonderfully named Bagheera kiplingi). They are generalists, pouncing on whatever comes within their reach. 

Insect pollinators have reasons to be particularly wary of one group of spiders: the crab or flower spiders (Family Thomisidae). Most of them are ambush predators: they sit perfectly still on a spot likely to be visited by insects, such as a flower, and wait for lunch to fly in. To make things worse for an inattentive insect expecting to collect pollen or get a sip of nectar, many flower spiders show some degree of crypsis, which is the ability to blend in with their environment to avoid detection (different from mimicry, which is disguising by resemblance to another organism). We can just say that flower spiders are very good at camouflage.

A female white-banded crab spider (Misumenoides formosipes) on a stakeout. She can change her colour between yellow and white to match the surroundings © Judy Gallagher, Wikimedia Commons.

Interestingly, flies are less susceptible to spider predation than bees, possibly because they have better vision and can avoid or dodge attackers. Bumble bees are also less likely to become prey than solitary bees and honey bees, just because they are larger and bulkier, so more difficult to capture. It has been suggested that the long proboscis and the swing-hovering flying pattern of some moths have evolved as predator avoidance mechanisms: the further from the flower and less static, the better chance of escaping a lurking spider. But it’s not only through killing that spiders disrupt pollination: their mere presence results in insects making fewer visitations and spending less time on flowers. As a result, pollination rates and therefore seed production can be reduced (e.g., Romero et al., 2011). 

Game over: a female crab spider (Thomisus onustus) capturing a bee © Alvesgaspar, Wikimedia Commons.

From the above, you may be tempted to go on a spider-killing spree in your garden to protect pollinators and pollination. That would a mistake. We have a limited understanding about the effects of predation on pollination, but there are no reasons for alarm. The numbers of flower visitors killed represent a fraction of their populations, so a spider wipe-out would not help anything. And because of the complexity of these interactions, there could be damaging consequences. 

The crab spider Thomisus onustus, found across Europe, reduces bee visitation to buckler-mustard (Biscutella laevigata) flowers. But spiders have no preference for bees: they will take anything that comes their way. So insects that feed on vegetative parts (leaves, petals, etc.) are likely to be the spider’s main victims just because they are more abundant than pollen or nectar collectors (Knauer et al., 2018). Without the spider, buckler-mustard could be munched away with impunity.

Crab spiders feeding on a furrow bee (Halictus sp.) and a cabbage moth caterpillar (Plutella xylostella) © A.C. Knauer (Knauer et al., 2018. Nature Communications 9, 1367).

In South America, the stingless bee Trigona spinipes visit fewer flowers of the pea-related Chamaecrista ramosa when crab spiders of the genus Misumenops are about. Which is good from the plant’s perspective because these bees are pollen robbers, that is, they help themselves to pollen without pollinating the flowers. But the carpenter bees Xylocopa ordinaria and X. hirsutissima, which are legitimate pollinators of C. ramosa, are not put off by the spiders, probably because they are too big and strong to be captured (Telles et al., 2019). So hosting a bee predator with restricted hunting abilities may be beneficial to the plant.  

A Mesumenops bellulus ready to give a deadly embrace, but not to portly carpenter bees © Judy Gallagher and Bob Peterson, respectively. Wikimedia Commons.

Spiders are one of most important groups of predators on Earth, with enormous influence in the natural world. Nyffeler & Birkhofer (2017) estimated that spiders kill the equivalent of 400 to 800 million metric tons of prey annually worldwide. More than 90% of this biomass comprises springtails and insects, including a vast number of domestic and agricultural pests. For comparison, the annual food consumption of all the world’s seabirds is estimated at 70 million tons.

Tables set for lunch. For an insect, it’s dangerous out there.

Spiders’ carnage is hugely beneficial: it regulates the numbers of abundant species, preventing them from taking over, and keeps insects with outbreak potential (pests) in check. And they are also essential food items to other creatures: wasps, frogs, lizards, birds and even fish feed on spiders, sometimes substantially.

You don’t have to be fond of spiders; but being aware of their ecological importance would make them more accepted and valued, even if at distance.

To the delight of J. K. Rowling, a new species of spider discovered in India in 2016 was named after Godric Gryffindor of sorting hat fame (Harry Potter series): Eriovixia gryffindori. New spider species are discovered all the time © India Biodiversity Portal and Suzelfe (Wikimedia Commons), respectively.

Johnny Cash, ‘The Man in Black’, was the source for the name of a new species of tarantula whose males are usually black: Aphonopelma johnnycashi. The spider was discovered near the California prison that inspired Cash’s song Folsom Prison Blues (1955). A. johnnycashi is one of the 14 new tarantula species recently found in the United States (Hamilton et al., 2016) © Hamilton et al., Wikimedia Commons.

Beds for Bees

In today’s guest blog we hear from Leigh Biagi whom many of our readers know through her excellent On the Verge work.  Here she explains a little about a new project she is involved in. Beds for Bees is the work of RePollinate, the charity arm of the Scottish Bee Company. Quite simply it offers funding and support to community groups who wish to make their local green spaces as pollinator-friendly as possible. 

“We know that pollinator numbers are declining due to several factors. Most significantly, the disappearance of many of our native wildflowers in the countryside as a result of intensive agriculture. 

“Moreover, research has shown that bees and other pollinators are starting to gravitate to our towns and cities attracted by the flowers in gardens and green spaces. Whilst it is preferable to make sure there are enough native wildflowers around to feed pollinators, in some urban spaces this isn’t always welcomed by local communities, as wildflower areas can be perceived as too untidy. Beds for Bees offers communities a tidier alternative to a wildflower meadow, but with all the pollen and nectar benefits for a wide range of pollinators. 

“The beds are designed to incorporate a careful selection of cultivated perennial and annual plants all of which will be highly attractive to bees and local residents alike. The creation of one of these beds might involve converting existing grassland (perhaps a park edge or in school grounds), but it could also include the use of existing community beds or planters.

“The scheme was originally piloted through On the Verge in 2021, and then adopted by RePollinate in 2022 to roll out on a national level. Last year RePollinate established nine Bee Beds, and have funding to work with more community groups this year. 

“The RePollinate team helps communities by providing a range of planting designs for different conditions, ensuring that each design delivers on variety in flower morphology for different pollinator groups. They don’t ignore the aesthetic impact and embrace harmonious and attractive colour arrangements, with variety in height structure, extended/sequential flowering, and low maintenance aspects factored in.

“What’s more they supply the plants, organising for them to be sent to the community group as near to planting time as possible. In addition, they cover the cost of peat free compost where needed and provide a sign for the site explaining the purpose of the bed. The sign includes a QR code which links back to the RePollinate website where more information is available.

“That element of providing guidance for the ongoing maintenance of the beds means that the community group can manage their own space thereafter. The information provided helps identify a suitable site and how to contact the landowner to obtain permission for the establishment of the bed. It also helps organise the preparation of the bed, and suggests that the group designate a member of their team to receive the plants and look after them until planting time.

“There is practical help when it comes to advice on when best to plant out the bed (usually late May/ early June) according to a logical planting plan.

“In return the team at RePollinate ask the community group to agree to maintain the bed for a minimum five-year period, with regular maintenance sessions. That’s not an onerous task as the beds are designed to be low maintenance and care plans are supplied.

“Spreading the word and encouraging others to follow suit is important, and groups are asked to send regular updates and photographs of their flower beds to RePollinate for use on social media.”

If you are interested in registering for the project or would like further information, please email leigh@repollinate.org.uk or nick@repollinate.org.uk 

https://www.repollinate.org.uk/

https://www.onthevergestirling.com/

Cleared for take-off

By Athayde Tonhasca

In the 1930s Germany, a renowned aerodynamics engineer was having dinner with a biologist when the conversation drifted to the subject of flying bees. The engineer, possibly animated by a sip or two of schnapps, showed the biologist some back-of-the-envelope calculations to prove that bees could not generate sufficient lift to fly. Apparently impressed by his interlocutor’s insight, the biologist went on to announce to the world the scientific proof that bees can’t fly. The press picked up on the story, and an urban myth was born – although this is only one of several tales explaining the origin of the widespread belief that scientists have proved that bumble bees can’t fly (nobody knows how bumble bees got involved).

But as bumble bees carry on stubbornly contradicting science by doing what they are not supposed to do – fly – one group of people found the explanation for this paradox: creationists. “Of course, our Creator God knows how to make a bumble bee fly, even if the best of modern science can’t figure it out” (Creation Moments, an American creationist broadcaster); “God created all living things, therefore, He knows exactly how to make a bumble bee fly, even when it defies logic, and when even the best of modern science can’t figure this thing out” (The Washington Informer, an American creationist publication).

A flying bumble bee: a miracle in action? © marsupium photography, Wikimedia Commons.

Alas, what the anonymous engineer proved to the gullible biologist was that 1930s mathematical models were too crude to explain the flight of a bee. The aerodynamics theories available then were based on observations and experiments with the rigid wings of an aeroplane. Under this model, a bee couldn’t possibly fly whatever wing-beat power it could muster; its wings are too small for its body size, and would generate too much drag.

But the flight of a bee is much more complex than an aeroplane’s. Her wings are not rigid structures that flap up and down; they bend, twist and rotate to make quick, arched and sweeping waves forwards and back. The angling of wings and a very high wing-beat frequency create vortices of low pressure under the bee, keeping her aloft. So bees are more similar to crude helicopters than to aeroplanes. Bees’ aerodynamics have been extensively studied and explained with no need for heavenly input (e.g., Sane, 2003. Journal of Experimental Biology 206: 4191-4208; Altshuler et al., 2005. PNAS 102: 18213-18218). 

The flight of a honey bee comprises up-and-down movements, forward-and-backward movements, and torsion (the partial rotary movement of the wing on its long axis). The wing tip describes a long, narrow and slanting figure of eight © Arizona Board of Regents / ASU Ask A Biologist.

But even with these intricate manoeuvres, flying is challenging for a heavy bee such as a bumble bee. She makes up for her weight problem with brute force, that is, by beating her wings up to 200 times per second. Such tremendous speed is only possible thanks to the bee’s morphology. Unlike birds and bats, bees’ flying muscles are not attached directly to the wings, but to the thorax. Dorsoventral muscles run from the top to the bottom of the thorax, and dorsal-longitudinal muscles run from the front to the back of the thorax (the wing muscles of mayflies, dragonflies and cockroaches have a different configuration). By alternating rhythmic pulsations of these muscles, a bee squeezes and expands her thorax, generating a great deal of energy that is channelled to wing-flapping at mindboggling speeds, akin to vibrations of a bowstring. Watch the whole cycle in slow motion, and the result in real life. 

A bee’s flying apparatus: the contraction of the longitudinal muscles and relaxation of the vertical muscles expand the thorax upwards and drive the wings downward. The relaxation of the longitudinal muscles and contraction of the vertical muscles pushes the thorax sideways, driving the wings upward © John R. Meyer & David B. Orr, North Carolina State University.

The buff-tailed bumble bee (Bombus terrestris) – and presumably other bumble bee species – makes her life even more complicated by flapping the left and right wings independently, which is an aerodynamically inefficient, let alone inelegant, way of travelling (Bomphrey et al., 2009. Experiments in Fluids 46: 811–821). But inefficiency does not stop bumble bees. Some species are capable of migrating hundreds of kilometres (albeit with the help of wind currents); others have been recorded living in montane habitats as high as 5,000 metres, where oxygen levels and temperatures are taxing to most flying creatures. The fittingly named Bombus impetuosus can go further up: males released inside a chamber with an atmosphere rarefied to pressures equivalent to an altitude of 9,000 m (higher than Mount Everest) could sustain flight by simply beating their wings in broader strokes (Dillon & Dudley, 2014. Biology Letters 10: 20130922). Cold and lack of food would prevent such an adventure, but not aerodynamics.

Fly over that mound? Not a problem for B. impetuosus © Rdevany, Wikimedia Commons.

Thanks to their high-energy fuel – nectar – bumble bees can easily fly for several kilometres in search of nectar and pollen. They can, but prefer not to. Shorter trips are more energy-efficient than long journeys, so bumble bees tend to stick around their nests (50 m to 2 km radius) as long as the surroundings are rewarding, food-wise. Other bees follow a similar pattern. Even small species can go over the 10 km mark, and the orchid bee Euplusia surinamensis seems to hold the record: a marked and released bee found its way home from a distance of 23 km through the jungles of Central America (Janzen, 1971. Science 171: 203-205).

The orchid bee E. surinamensis, a long distance flyer. Art by Dru Drury, 1770. Wikimedia Commons.

Bees’ flying distances are usually correlated with body size, but overall they tend to maximise energy gains by keeping foraging expeditions short. This has implications for the management of pollinators. As a general rule, based on results from a number of bee species, flower patches are best placed within a few hundred metres of each other to facilitate foraging and reduce the risk of bees running on empty (Zurbuchen et al., 2010. Biological Conservation 143: 669–676). 

The flight of a bee is not mysterious or miraculous, but it is a complex and demanding activity. Bees resort to it judiciously for their survival. 

Tagging is a common method to estimate bees’ flying ranges. A: Chelostoma florisomne; B: C. rapunculi; C: Heriades truncorum; D: Hoplitis adunca; E: Osmia bicornis; F: O. cornuta © Hofmann et al., 2020. Journal of Hymenoptera Research 77: 105–117.