The graveyard shift: the elusive side of pollination

By Athayde Tonhasca

If you take a stroll through your local garden after sunset, it will look and feel like another place. Under reduced light, white or pale flowers with long corollas are likely to stand out among all the others. The smells are different, thanks to ornamental plants that release more scent at night such as sweet rocket (Hesperis matronalis), jasmine tobacco (Nicotiana alata), mountain tobacco (Nicotiana sylvestris) and evening primrose (Oenothera biennis). You wouldn’t be able to tell, but some of these plants also produce more nectar at night.

All these traits – flowers shape and colour, nocturnal opening, scent release and nectar production – suggest these plants are specialised in attracting moths for the purpose of pollination. This is indeed the case for many species: some European orchids and campions (Silene spp.), as well as many plants elsewhere, depend on moths for pollination. But compared to bees and flies, we know little about moths’ role as pollinators.

We may think that a flower visited is a flower pollinated. But, more often than not, this isn’t the case. Sometimes the visitor is interested in nectar only, craftily avoiding contact with the floral reproductive structures and getting stuck with annoying pollen grains (this is the case for most butterflies). Some insects groom themselves efficiently to remove all excess pollen, others consume it all; the interval between flower visits may be too long, so that pollen is no longer viable; visitors may deposit the pollen on the wrong plant; or the number of pollen grains deposited is insufficient. The reasons for pollination not happening are numerous.

The most reliable method to determine whether a visit results in pollination is to measure the number of pollen grains deposited on a virgin stigma during a single contact: pollination ecologists call this metric Single Visit Deposition, or SVD. But this is not an easy figure to come by; it demands meticulous and laborious work. So it is not surprising that SVDs have been estimated for a handful of plant-pollinator couplings.

Moths from the families Noctuidae (L) and Sphingidae (R), two important flower visitors. (C) Olaf Leillinger (L) and Sharp Photography (R), Wikipedia Creative Commons.

Because SVDs are tricky, researchers often use pollen load as a proxy. This is the number of loose pollen grains attached to the insect’s body, which has been shown to correlate with SVD. Counting is done directly on the insect or on the residue left after washing it with a cleaning solution. You may say, correctly, that this is not particularly easy either. But it is easier and more practical than estimating SVD.

After lots of counting, we have learned that pollen loads of bees are in the thousands, and range from lower thousands to hundreds in flies. Moths on the other hand carry a few dozen to a handful of pollen grains. These figures don’t look good as a pollinator’s credentials. However, pollen loads do not tell the whole story. Hairiness and size have to be taken into account as well. Hairy insects have more pollen stuck to them, and big insects are more likely to contact stigma and stamen at the same time, leading to greater pollen transfer. Behaviours such as visit duration and flower constancy (the tendency to visit the same flower species) are also important.

This hirsute moth has what it takes to be a pollinator. (C) Commonwealth Scientific and Industrial Research Organisation, Wikipedia Creative Commons

There are over 2,500 species of moth in the UK, and many of them tick some of the boxes required to identify a pollinator: they are large and abundant, they visit the same plant species frequently, and they are covered with ‘hair’ (hair-like scales). Between 8 and 80% of them transport some pollen from a range of plants, depending on the habitat.

So we just don’t know to what extent moths contribute to the pollination of wild plants and crops. This isn’t surprising, considering they are not studied very often because of their unsociable hours. We are more likely to see moths circling lampposts or caught in light traps than visiting flowers.

A survey commissioned by Butterfly Conservation revealed that 74% of the UK population have a negative opinion of moths. Many people believe they are pests (a handful are) and eat clothes (two species do). But the overwhelming majority are harmless and have enormous importance in the food chain: for example, they are the main course in bats’ dinners. Pollination may very well be one more ecological service provided by these secretive night flyers so busy in our gardens while we sleep.

A rural revival

Change is afoot. A key intention in the farming payments sphere is now based around positive contributions to nature, and you may have noticed in the press recently that a new environment-friendly payment system is being worked up by DEFRA in England. In Scotland there is considerable interest in this concept.

Local Authorities, environmental bodies and thousands of individuals have been creating pollinator-friendly habitat with considerable success in an urban setting for some time.  Now the evidence is pointing to similar strides being taken in our countryside and particularly around our farms.

Melancholy thistle (Cirsium heienoides) growing in an upland hay meadow at Glen Fender, Tayside and Clackmannanshire Area. ©Lorne Gill/NatureScot

Subsidies and payment are a key part of the modern farming world, and any political transition opens up the possibility of an awkward move from one system to another. But with a drive to ensure that improving productivity and delivering for nature work hand-in-hand there is a huge desire to ensure that any transition works well.

We’ve long recognised the links between farming and pollinators in Scotland.  Much is made, rightly so, of the fact that the UK has lost around 97% of its wildflower meadows since the Second World War, and redressing that loss is a huge task. Nevertheless, if we are to better manage and create habitat for pollinators it’s a challenge we have to face immediately.

Surveys last summer, funded by NatureScot, showed that a significant number of Scotland’s Agri-Environmental Climate Scheme (AECS) options improve habitat for pollinators including those for hedgerow management and creation, wild bird seed, water margins and species rich grassland. Farms under the scheme had a higher number and diversity of pollinators.   The impact of the AECS scheme is significant, area of species rich grassland and habitat mosaic managed amounted to more than 55,000 ha with a committed funding of £20 million.

Equally heartening is the realisation that the Scottish Government funded Farm Advisory Service (FAS) provides specific information on pollinators to farmers @  Materials include videos, technical notes, advice on both Integrated pest Management (IPM), and on monitoring pollinators. Farm events delivered by FAS have complemented these materials. 

Across the Irish Sea our pollinator counterparts have also made impressive strides in connection with the farming community and seeking solutions to help pollinators.  Their work on payment-by-results schemes, backed by tapping into EU funding, is revolutionary and they are leading the way within Europe on an innovate approach to transforming land management support.   

NatureScot appreciates the need to look forward and recently recruited a graduate placement to actively encourage ‘the benefits of managing land for nature’.  This is an exciting role that will enable ever-stronger connections between our organisation and the farmer blending the experience we each bring to the subject matter. 

Farming of course is an ever-changing subject. With new research comes new approaches and the knowledge base around this key industry rarely stand still.  A combination of bodies including SRUC, James Hutton Institute, and Edinburgh University are looking at pollinators in relation to farming across several projects.  Included are projects studying unmanned aerial vehicles to monitor pollinator assemblages, the potential of Nitrogen-fixing crops to provide resources for insect pollinators, the impact of agri-environmental interventions on beneficial insects, ecosystem service delivery at the farm scale and assessing the links between oilseed rape and pollinators. That’s a broad sample and a wide view in any language, but it’s key to making sure we mould farming activity and pollinator-friendly practise in the best way possible. 

There has always been a fascinating connection between farming and pollinators. As our political landscape, economic backdrop, climate change and technical knowledge converge this relationship is set to remain ever vital and adaptable.

Further reading @

Between art and science, between nature observation and artistic intention

By Athayde Tonhasca

Ovid’s poem Metamorphoses (8 AD) is a collection of mythological and legendary stories with a central theme of transformation or metamorphosis, from the Greek meta (change) and morphe (form). The poem has had a profound influence on Western literature and art, so classicist-inspired biologists and naturalists had a perfectly fitting word to describe one of the most fascinating and baffling biological phenomena: metamorphosis. 

This is the process in which some insects and other animals undergo radical change in form and function when growing from immature to adult phases. This transformation requires the complete dissolution of the animal’s internal organs and their reassembly into a new creature entirely: see an example of a caterpillar turning into a butterfly. The mechanisms and chemistry of metamorphosis are still not fully understood.

Metamorphosis seems so disconcerting that for centuries nobody would consider that larvae and adult insects were the same animal. That view began to change with the work of Jan Goedart (1617–1688) and Jan Swammerdam (1637–1680), Dutch naturalists and entomologists who demonstrated that larva, pupa and adult insect were phases in the development of a single individual. 

Goedart’s and Swammerdam’s drawings and descriptions did not go unnoticed by a young German expat, Maria Sibylla Merian (1647-1717), a woman with a remarkable biography. Since her teenage years, Merian painted, collected and studied plants and insects, particularly moths and butterflies. She married and started a family, but never abandoned her art and scientific investigations. After leaving her husband, she moved to Amsterdam, supporting her two daughters through her publications, selling hand-mixed paints and linens, and teaching painting and embroidery to young women.

In 1699, at the age of 52, Merian and her youngest daughter left for Surinam, then a Dutch colony. In a venture that would be considered bold and risky today, the Merians travelled alone through the South-American jungle for two years, observing, drawing and collecting plants and animals. Merian was one of the first people to record parasitic wasps emerging from the cocoon of a moth or butterfly, and the metamorphosis of a tropical butterfly. The two women returned to Amsterdam two years later, loaded with preserved animal and plant specimens. Merian published her book about her studies, Metamorphosis insectorum Surinamensium, and continued painting, publishing and trading specimens until her death.

Artist-naturalists of the period were predictable and formal: they usually depicted specimens singly against a neutral background. But Merian drew and hand-coloured animals and plants in their surroundings and interacting with each other. Her paintings were descriptive, for example showing a flower reproductive cycle from bud through fruit. Or all the stages of a butterfly, from caterpillar to imago (the adult, mature stage), host plants included. Merian’s plates portrayed ecological communities and species interactions almost two centuries before German zoologist Ernst Haeckel coined the term oecologie, which was the foundation for the new scientific field of Ecology.

Metamorphosis insectorum Surinamensium, M.S. Merian, 1705. Images in the public domain.

Merian’s artistic style become a standard for scientific illustration, still in use in today’s nature guides. Through her beautiful and accurate art and observations, Merian made metamorphosis and other biological phenomena widely known, and helped dismiss the entrenched belief that insects generated spontaneously. 

Merian was respected and acknowledged by fellow naturalists of her generation. Carl Linnaeus would later classify insects based on her drawings, and Goethe, who was a poet and a naturalist, celebrated Merian for her ability to move ‘between art and science, between nature observation and artistic intention.’ But eventually her work was forgotten until the 1970s, when the Soviet Academy of Sciences republished her paintings. The world rediscovered Merian’s achievements, and she has been celebrated in currency, postage stamps, academic publications, books and museum exhibitions. A genus of plants (Meriania), a lizard (Salvator merianae), a toad (Rhinella merianae), a spider (Metellina merianae), among other species, have been named in her honour.

These accolades are well deserved. Maria Sibylla Merian was the woman who made science beautiful.

The seeds of a great idea

Some people have boundless energy. Take Alex Stuart, who works with the James Hutton Institute, and is also Local Biodiversity Coordinator for the North East Scotland Biodiversity Partnership. She helped to persuade around 550 colleagues to plant one-square-metre patches of wildflower seeds during lockdown in order to ensure pollinators got a helping hand, and colleagues enjoyed a welcome health and wellbeing benefit.

The inspirational idea emerged very early on in lockdown. The James Hutton Institute asked Alex to help lead on a project to provide all staff members with some wildflower seeds from Scotia Seeds, offer a little advice on how to prepare and sow, and then measure the results.

It was a positive way for the organisation to support staff’s physical and mental well-being during the gruelling spell of lockdown.  Moreover, it was a chance to benefit nature and the local environment.

Alex takes up the story, “During our time in lockdown, the UK saw an unprecedented upsurge in gardening. As the nation found itself restricted in time spent outside of their homes, it was only natural to try and make the best of the green areas which we could access and interact with – our gardens. The benefits of gardening are also well-documented as reducing anxiety and depression, improving cognitive function and increasing a sense of community. We can all benefit from spending some time outside getting our hands dirty, and that includes our local wildlife too.

“With this idea in mind, the Institute sent each member of staff and its UK-based students a small pack of native wildflower seeds with the aim of creating a 1 square metre area of wildflowers. The pack included easy to follow instructions on how to prepare the area for sowing, and the required aftercare.

While most people may be aware that our native wildflowers are in decline across the country, the extent of this decline is far greater than most realise. Since World War 2, the UK has seen the drastic loss of 97% of its wildflower meadows, due to factors such as land development and changing agricultural practices.

When wildflower meadows disappear so do the pollinators, as well as other insects, which rely on these wildflowers for food and habitat. A recent study showed a third of our wild bee and hoverfly species in decline across the country since the 1980’s, with losses focusing on our rarer species. This of course has knock-on effects for other animal species who rely on these insects for food, including birds, bats and other small mammals.

Sowing native wildflower seeds in gardens at home may not contribute to their conservation in the wild, but it will help provide for our struggling pollinators, many of which have specific associations with wildflower species. For example, some insect species are solely reliant on one plant species, e.g. the larvae of the Small Blue Butterfly will only live on the flowers of the Kidney Vetch.  Without that one species of plant, that insect will become extinct!

“We realised that for many people, this would be the first time that they had attempted to grow wildflowers! Perhaps a bit daunting for those not green-fingered, but the activity was actually one that could easily be done involving small children.  Also compared to most plants, wildflowers require only a small amount of care and maintenance each year.

“As well as the activity of getting outside and sowing the seeds, once the plants were established, we expected our colleagues to see some new insect visitors to their  wildflower area. Every wildflower in the mix was known to have some association with types of Bees, Wasps, Moths, Butterflies, Hoverflies, or Beetles.

“To help with species identification we drew on the expertise within the Institute and offered the following links along with the seed packs:

  • Buglife  Pollinator identification chart for the most common insect visitors.
  • A pollinator ID guide for children helped the smaller members of the family learn a bit more about their local nature
  • A list of the known pollinator associations for the wildflowers in the seed mix was also provided

“We encouraged staff to take pictures or videos of their progress. I’d say we were confident the seeds would do well in the right conditions. The wildflower seeds we provided were sourced from Scotia Seeds, which is the only large-scale producer of Scottish native wildflower seeds of wild origin within Scotland.  This means that, unlike generic seed mixes from elsewhere in the UK, Europe or even as far away as America, these seeds are actually adapted to growing in our Scottish climate.  This is important because the seeds have better germination rates, produce more flowers and most importantly flower at the right time of year for our local insects.

“The seed mix was the ‘Get Nectar-rich Quick Mix’, which contains a mixture of 24 annual, biennial and quick-growing perennial wildflowers, which means that flowers came through in late summer and some should do so again in years to come.  

“The list of plant species in our packs was impressive. It contained many popular species including:  (Annual) cornflower, corn marigold, mayweed. (Biennial) teasel, viper’s bugloss, weld. (Perennials) yarrow, clustered bellflower, common knapweed, field scabious, meadow cranesbill, wood cranesbill, rough hawkbit, ox-eye daisy, wild marjoram, selfheal, red campion, ragged robin, white campion, bladder campion, hedge woundwort, red clover, tufted vetch, and bush vetch.

“The advice we gave was hopefully easy to follow and should stand our colleagues in good stead if they want to spread the word to friends and family. In general, the ground required to be prepared for sowing by removing any existing vegetation from the area, preferably pulling it out by hand or cutting it short and then digging it in. The soil then needed to be prepared for seeding by making it as smooth as possible. To do this, we suggested our gardeners break down any bigger clumps with a fork and then repeatedly raked it over until the soil texture was fine. Ideally this prepared soil was left for a week or two so any dormant weeds or grasses that came to life could be removed before anyone sowed seeds.

“Of course, wildflower seed sowing should be done on a calm day, as seeds are often very small and can easily be blown away. Spring sowing can take place up until the end of June, but should be done as early as possible, as later sowings are more vulnerable to effects of drought. We also suggested that colleagues add some sharp sand or flour to their wildflower seeds to help identify where they had sown. The seed mix was to be spread evenly across the 1 marea – which might have looked like a tiny amount, but we stressed that folk shouldn’t be tempted to over-seed a smaller area, as the plants required space to grow.  Finally we urged that the ground was very gently raked over so that seeds were just barely covered and then finally we asked that everyone pressed the seeds down by trampling the area by foot – think penguin walking was our advice!

While most of us are lucky to have our own garden, we recognised that some may not be, or the garden may be shared with others or be not suitable for this kind of planting. One alternative we offered was to plant up the seeds in large pots or containers. Wildflowers do need a fair amount of space to grow, so smaller pots will not be suitable in the long term. Grow Wild have some good advice on planting up wildflowers in containers.

“Small pots could however be used to grow the seeds on as small plug plants, which could then be relocated at a later date, for example to a friend or family member’s suitable garden.   

“As well as some do’s we offered one of two don’ts.  For example, we do not endorse guerrilla gardening – so were quick to ask that folk did not go out into the countryside or local public greenspace and sow the seeds there! We pointed out that you must always have the permission of the landowner before sowing/planting anything.

“Our approach will help pollinators but we accept it was a localised action. There are obviously some benefits and downsides of having the 550 m2 spread out across the landscape. For example, one large field of the same area may be able to act as more of a stronghold for pollinator species, but that would depend on pollinators being able to make their way there. Habitat fragmentation and habitat loss are big contributing factors to the loss of pollinators – it is becoming increasingly hard for them to find enough of the right food sources and travel between these areas. By having small pockets of pollinator-friendly flowers across the city and countryside we are hopefully improving the ability of insects to move more easily across bigger areas.”

You can read Alex’s inspirational blog in full on the James Hutton Institute website @  In the  meantime was a fabulous idea and well done to everyone involved.

Trees in the sky

By Athayde Tonhasca

Milan, Italy’s second largest city, is a chaotic and grey sprawl. In 2008, it was awarded the unenviable title of the most polluted city in Europe. Things have improved since then, but the city is not the best spot for a nature-themed holiday. So a visitor wandering into the Porta Nuova district may be surprised to come across the bosco verticale (vertical forest), two verdant columns sticking out from a surrounding monotony of brick and concrete. These residential towers support over 20,000 plants, of which approximately 800 are trees. Plant species were distributed around the buildings and above ground according to their requirement to light exposure. Altogether, the bosco verticale is equivalent to an area of 3 hectares.

Bosco verticale, Milan @ Athayde Tonhasca

The vertical forest received several architecture and design awards, and is praised for its contribution to improving Milan’s air. The buildings’ vegetation absorbs about 19 t of CO2 per year, which corresponds to a similar volume of oxygen produced. 

These buildings were not designed with pollinators in mind, but the concept is transferrable: many nectar and pollen-producing shrubs and trees could be used in similar structures.  If you are wondering whether pollinators would benefit from trees high up in a building, the answer is ‘yes’. Trees have the advantage of providing greater food density. The 3-dimensional space of a tree canopy can offer more flowers than an equivalent area of wildflower meadow. For foraging efficiency, pollinators are mostly attracted to flower clusters, so flowering trees act as a magnet to pollinators that can benefit the surrounding vegetation.

Planting perennial and annual wildflowers is one of the main practices for addressing the decline of some pollinators, and trees are rarely considered in conservation plans. But this is an oversight. Trees such as blackthorn (Prunus spinosa), cherries (Prunus spp.), maples (Acer spp.), willows (Salix spp.), alder (Alnus glutinosa), crab apple (Malus sylvestris), elder (Sambucus nigra), hawthorn (Crataegus monogyna) and rowan (Sorbus aucuparia) are important sources of pollen or nectar for several bee and hoverfly species, as well as for other insects. Interestingly, many trees that are good pollen sources are anemophilous (wind pollinated), like the northern red oak (Quercus rubra), or ambophilous (pollinated by wind and insects), such as several willow species. Planting an oak tree on a flat’s balcony is not a good idea, but other trees of manageable size are available. 

In the UK, domestic gardens are usually small, but altogether they cover 18 to 27% of our urban areas. Because of the concentration of flowers and nesting sites, gardens can support a greater diversity and abundance of pollinators than surrounding farmland. Parks, allotments, churchyards, woodland and brownfield (derelict land) sites are other city spaces with similar potential as good pollinator habitats. Clever, well-planned planting of trees on rooftops and balconies can be one more management option for pollinators. 

The United Nations has predicted that 66% of the world’s population will to be living in built-up areas by 2050. In the UK, about 80% of the population is already concentrated in urban spaces, which take up almost 7% of the land area. Creative city planning can make a small but not negligible contribution to the conservation of pollinators and pollination services, making cites better places for us and the other species that share our habitat.

Bosco verticale, Milan @ Athayde Tonhasca