Pollinators by Jim Pearson

 Hummingbid hawk-moth



Cross-pollination often relies on carriers (vectors) to move pollen, including wind, water, birds, insects, butterflies, bats, etc.

We call animals that transfer pollen from plant to plant “pollinators”.

Pollination is often the incidental consequence of an animal’s activity on a flower. The pollinator is often eating or collecting pollen for its protein and other nutritional characteristics or it is sipping nectar from the flower when pollen grains attach themselves to the its body. When the animal visits another flower for the same reason, pollen can fall off onto the flower’s stigma and may result in successful reproduction of the flower.


Pollination by Insects


There are at least 1500 species of insect pollinators in the UK. The honey bee normally lives in hives managed by beekeepers. Others, like many species of bumblebees, solitary bees, flies (especially hoverflies), wasps, moths, butterflies and beetles live in the wild.


Fig: 1: An elephant hawkmoth (Deilephila elpenor) using its long proboscis to probe honeysuckle flowers (Lonicera periclymenum) after dusk


A study by a team from the Centre for Ecology and Hydrology (CEH) in Wallingford, Oxfordshire looked at trends in 353 wild bees and hoverflies in Scotland, England and Wales over 33 years from 1980. AThey found third of species experienced declines in terms of areas where they were found, while about 10% became more abundant, including bees that pollinate flowering crops, such as oil seed rape.

While some pollination is carried out by honeybees in hives, much of the pollination of food crops and wild plants is carried out by their wild relatives and other insects, especially hoverflies.

Dr Powney, the team leader, said while the increase in key crop pollinators is "good news", species have declined overall and that "It would be risky to rely on this group to support the long-term food security for our country … If anything happens to them in the future, there will be fewer other species to step up and fulfil the essential role of crop pollination."

The article suggests if current trends continue, some species will be lost from Britain altogether and that there are "winners" and "losers" among hundreds of wild bees and hoverflies, which pollinate food crops and other plants with common species winning out at the expense of rarer ones, with an overall loss of biodiversity.1

Fig. 2: Many British pollinating insects in decline, study shows


The losses were concentrated among the rarer, specialised species. The "losers" include solitary bees, which live in burrows in the ground, and upland bees, living on mountains and moorlands. Among the "winners" are 22 of the most important crop pollinators.

"Every square kilometre in the UK has lost an average of 11 species of bee and hoverfly, between 1980 and 2013, according to the new analysis," said Dr Lynn Dicks of the University of East Anglia.

She said the pattern of biodiversity loss is happening everywhere we look … "It's a process of homogenisation and leaves us with a natural world that is far poorer and less resilient to change.2 3


Pollination by Bees

There are over 250 species of bee in the UK: 25 species of bumble bee, 224 species of solitary bee plus 1 honey bee species made up of 2 subspecies, 1 ‘introduced’ form, Apis mellifera’ and 1 newly discovered native form Apis mellifera mellifera.

Bees are perhaps the most important pollinators of many garden plants and most commercial fruit trees.



Since bees cannot see the colour red, bee-pollinated flowers usually have shades of blue, yellow, or other colours. Bees collect pollen or nectar visiting flowers that are open during the day, are brightly coloured, have a strong scent, and have a tubular shape, typically with the presence of a nectar guide.

There have been many reports about the declining population of honeybees suggesting many flowers will remain unpollinated if honeybees disappear with a subsequent devastating impact on many food crops.4 5 6

A 2019 study by conservation charity Buglife Northern Ireland that examined historical and modern data has suggested that 21 bee species in the province are at risk of extinction unless action is taken.7

However, a Curtin University study has found the introduced European honeybee could lead to native bee population decline or extinction when colonies compete for the same nectar and pollen sources in urban gardens and areas. Researchers found introduced honeybee may pose threat to native bees. This calls into question both the advisability of promoting bee-keeping as a leisure activity and the conflation in the minds of many public bodies with honeybees as pollinators with all other pollinators.8


Pollination by Flies

Fig. 4: Female Bombylus major in Regents Park London


There are around 7000 known species of flies known in the UK. Most flower-visiting flies have large eyes and at least the higher developed flies have colour vision which aids finding flowers from afar.

In contrast to many bees, flies still fly in less favourable weather conditions and on cold, windy and overcast days flies are often the only flower visitors you will see. Plants growing in damp, shady places such as woodlands would struggle to attract bees but flies are often abundant in these places and quite a lot of woodland plants get pollinated by flies and not by bees.

Short-tongued flies are often attracted to yellow and white flowers or brown/dark purple flowers while longer-tongued flies are also visiting purple and blue flowers which often have more deeply seated nectar than flowers of other colours.

Many flies are attracted to flowers that have a decaying smell or an odor of rotting flesh, carrion, dung, humus, sap and blood. These flowers, which produce nectar, usually have dull colours, such as dark brown or purple, sometimes flecked with translucent patches. They are found on the corpse flower or voodoo lily (Amorphophallus), dragon arum (Dracunculus), and carrion flower (Stapleia, Rafflesia).

Some flies locate suitable flowers by following the distinctive flower scent which they detect with their antennae. Most flower-visiting flies also have large eyes and at least the higher developed flies have colour vision which helps with finding flowers from afar.

Other important groups of flower-visiting flies are the root-maggot flies (Anthomyiidae), house flies (Muscidae) and Fanniidae (no common name). All are relatively small flies and they like to visit sweet-scented flowers such as meadowsweet (Filipendula ulmaria), rowan (Sorbus aucuparia), crap apple (Malus sylvestris), willows (Salix spp.), ladies bedstraw (Galium verum) and thrift (Armeria maritima). They also seem attracted to sweet-scented flowers with a tang of stale dung or urine smell such as cow parsley (Anthriscus sylvestris), sweet alyssum (Lobularia maritima) and oil-seed rape (Brassica napus).

The bee-flies (Bombyliidae) include some of the most highly specialised flower feeders among the flies and are often medium-sized hairy flies with a very long slender proboscis. They often visit relatively large long-tubed flowers such as primroses (Primula vulgaris), cowslip (Primula veris), honesty (Lunaria annua) and wallflowers (Erysimum cheiri). Similar to hoverflies, bee flies are able to remain stationary in the air and usually hover in front of flowers when feeding. Bee flies are highly-developed nectar feeders and move rapidly from flower to flower to drink nectar. As they are early-flying they can be important pollinators of early spring flowers.9


Pollination by Hoverflies


There are over 280 species of hoverflies in Britain. After wild bees, hoverflies are the second-most important pollinators in the U.K.


Fig. 5: Why are hoverflies so important for our food system?


As regular flower visitors to a wide range of plants and agricultural crops, hoverflies are some of the most important pollinators in many ecosystems. Hoverflies are “incidental” yet crucial pollinators. The adults hover – as their name suggests – like hummingbirds over flowers to drink nectar. Although they can’t carry as much pollen on their bodies as bees, they can travel greater distances and make more flower visits. Like bumblebees, most hoverflies are generalists and will visit many different types of plants; however their preference is thought to be for yellow and white flowers.

Hoverflies often like to visit open cup-shaped flowers or small tubular flowers with easily accessible nectar such as buttercups (Ranunculus spp.), anemones (Anemone spp.), potentillas (Potentilla spp.) and many flowers from the daisy family (Asteraceae) and carrot family (Apiaceae) such as ox-eye daisy (Leucanthemum vulgare), thistles (Cirsium spp.), dandelion (Taraxacum agg.), calendula (Calendula officinalis), fennel (Foeniculum vulgare) and wild carrot (Daucus carota). Pollen-eating hoverflies are also often visiting poppies such as corn poppy (Papaver rhoeas) and Californian poppy (Eschscholzia californica) which produce no nectar but offer an abundance of pollen.

Hoverflies favour small, flat flowers that allow easy access to nectar, such as Daisies, Queen Anne’s Lace, Alyssum, Cosmos, Lavender, Zinnias, mint, and other small, flat flowers that allow easy access to nectar.

Most hoverflies visit flowers for nectar but some hoverflies such as some Melanostoma spp., Syrphus spp. and Episyrphus balteatus (Marmalade hoverfly) are specialised pollen feeders and often visit flowers just to feed on the pollen.10 11 12 13 14


Pollination by Wasps

There are over 7,000 wasp species living in the UK, comprising a huge variety of solitary and social species.


Fig. 6: Common Wasp (Vespa vulgaris) covered in pollen.


Social wasps such as the Common Wasp (Vespa vulgaris) are very important pollinators and will visit many different types of flowers and their role is often under-appreciated. Compared to the social wasps solitary wasps are not the most important wasp pollinators, although their contribution is still important.

Wasps are incidental pollinators whilst searching for nectar, by travelling from plant to plant carrying pollen. While their contribution to pollination may not be as substantial as bees', wasps still play a valuable part.

A study, published in Biological Reviews, compiles evidence from over 500 academic papers to review how roughly 33,000 species of stinging (aculeate) wasps contribute to their ecosystems. The researchers found evidence of wasps visiting 960 plant species. This included 164 species that are completely dependent on wasps for pollination, such as some orchid species that have evolved adaptations to attract the wasps they rely on, such as an appearance that mimics the back end of a female wasp. The researchers also say wasps could serve as ‘backup pollinators’ if a plant loses its local primary pollinator.15 16


Pollination by Butterflies


Fig. 7: Monarch butterfly


Butterflies, such as the monarch, pollinate many garden flowers and wildflowers, which are usually found in clusters. These flowers are brightly coloured, have a strong fragrance, are open during the day, and have nectar guides. The pollen is picked up and carried on the butterfly’s limbs. UK butterflies include well-known species like the Peacock and Red Admiral, as well as rarer species like the strangely-named Dingy Skipper, Silver Studded Blue (pictured) and the stunning Purple Emperor. Butterflies are capable of covering larger areas than bees and unlike bees they can see the colour red.

Dr David Lees, Curator of Microlepidoptera (micromoths) at the Museum says, 'There are just 57 resident butterfly species in the UK, compared to more than 2,500 moth species …Due to this low species diversity, butterflies are not as important for pollination as some other insects, but their abundance in florally diverse meadows and chalk downlands, for example, can sometimes make them more important than moths for pollinating flowers during the day.'17

Research by Butterfly Conservation in collaboration with partners shows 76% of butterflies have declined in abundance or distribution since 1976. Larger moths have declined by 33% since 1968.

“Right now, we are facing a man-made disaster of global scale. The twin challenges of climate change and biodiversity loss are pushing much of the natural world to the brink – including many of our most treasured species. In the UK, the majority of our butterfly and moth species are in worrying decline.

These beautiful and fascinating creatures are not just important in their own right, but are also indicators of a healthy environment for all wildlife. Over the next five years, Butterfly Conservation is committed to delivering the biggest possible impact for nature, playing a leading role within the conservation sector, with our new, ambitious strategy."

Chris Packham18


Pollination by Moths

Moths are important pollen transporters in English farmland and might play a role in supporting crop yields, according to a new UCL study.

The research, published in Biology Letters, shows that moth-pollen transport networks are larger and more complex than networks for daytime pollinators.


Fig. 8: Elephant Hawk moth: The nocturnal pollinators: scientists reveal the secret life of moths

The team found that moths transport pollen from a high number of plants also visited by bees, butterflies and hoverflies, but also interacted with plants not commonly visited by these insects. The study also shows that pollen transport occurs most frequently on the moth’s ventral thorax (chest), rather than on the proboscis (tongue), allowing it to be easily transferred to other plants.

Lead author, Dr Richard Walton said: “Nocturnal moths have an important but overlooked ecological role. They complement the work of daytime pollinators, helping to keep plant populations diverse and abundant. They also provide natural biodiversity back-up, and without them many more plant species and animals, such as birds and bats that rely on them for food, would be at risk.

“Previous studies of pollen transport among settling moths have focused on their proboscis. However, settling moths sit on the flower while feeding, with their often distinctly hairy bodies touching the flower’s reproductive organs. This happy accident helps pollen to be easily transported during subsequent flower visits.”

This pivotal study comes at the time as moth populations are experiencing steep declines across the globe, with worrying implications that we may be losing critical pollination services at a time when we are barely beginning to understand them.

Dr Jan Axmacher (UCL Geography) said:

“In recent decades, there has been a lot of science focus on solitary and social bees driven by concerns about their dramatic decline and the strong negative effect this has had on insect-pollinated crop yields. “In contrast, nocturnal settling moths - which have many more species than bees - have been neglected by pollination research. Our study highlights an urgent need for them to be included in future agricultural management and conservation strategies to help stem declines, and for more research to understand their unique and vital role as pollinators, including their currently unknown role in crop pollination.”

The study was conducted during the growing seasons (March-October) of 2016 and 2017 at the margins of nine ponds, located within agricultural fields in Norfolk, eastern England (UK).

Nocturnal moth communities and daytime pollinators were surveyed once a month to see which plants they visited and how frequently.

Of the 838 moths swabbed, 381 moths (45.5%) were found to transport pollen. In total, pollen from 47 different plant species was detected, including at least 7 rarely visited by bees, hoverflies and butterflies. 57% of the pollen transported was found on the ventral thorax of the moths.

In comparison, daytime pollinators, a network of 632 bees, wasps, hoverflies and butterflies, visited 45 plant species, while 1,548 social bees visited 46 plant species.

Dr Walton concluded:

“While bumblebees and honeybees are known to be super pollinators they also preferentially target the most prolific nectar and pollen sources … Moths may appear to be less effective pollinators by comparison, but their high diversity and abundance may make them critical to pollination in ways that we still need to understand. Our research sheds light on a little known world of nocturnal plant-insect interactions that might be vital to the look and smell of our precious countryside and to the crops that we grow.”


Moths, on the other hand, pollinate flowers during the late afternoon and night.19

Fig. 9: Hummingbird hawk-moth, Macroglossum stellatarum


Pollination by Beetles


Fig. 10: A rose chafer (Cetonia aurata) clambering over a pollen-laden flower

According to the Natural History Museums’ Senior Curator of Coleoptera Beulah Garner, 'Beetles have been pollinating flowers for millions of years, even before the dinosaurs evolved … over this time, evolution has perfected the insect-plant relationship and both insects and plants have evolved a great diversity of form and function.'

Many different species of beetles eat pollen. For some, such as the aptly named pollen beetles, pollen is their main diet. For others, it is an additional tasty snack, including for some ladybirds that supplement their usual carnivorous diet of aphids with pollen.

Beetle-pollinated flowers tend to make extra pollen so there is some left over to be carried to another flower on the beetle's body.

The flowers tend to be smelly or fragrant, because beetles navigate by a strong sense of smell. Beetles are attracted to flat, open flowers, which allow them to graze, and flowers in clusters, such as cow parsley.

Approximately a quarter of the UK's beetles are pollinators - so around 1,000 species. These include flower beetles, longhorn beetles, pollen beetles, soldier beetles, sap beetles, checkered beetles and scarabs. Some beetles are just incidental pollinators, moving pollen as they go about their daily business.17


Nectar guides

Nectar guides, which are only visible to certain insects, facilitate pollination by guiding bees to the pollen at the centre of flowers.


Fig. 11: Images of a Mimulus flower in visible light (left) and ultraviolet light (right) showing a dark nectar guide that is visible to bees but not to humans


Insects and flowers both benefit from their specialized symbiotic relationships; plants are pollinated while insects obtain valuable sources of food.

Nectar guides are markings or patterns seen in flowers of some species, which guide pollinators to their rewards. Rewards commonly take the form of nectar, pollen, or both, but various plants produce oil, resins, scents, or waxes. Such patterns also are known as "pollen guides" and "honey guides.

Pollinator visitation can select for various floral traits, including nectar guides through a process called pollinator-mediated selection.

These patterns are sometimes visible to humans; for instance, the Dalmatian toadflax (Linaria genistifolia) has yellow flowers with orange nectar guides. However, in some plants, such as sunflowers, they are visible only when viewed in ultraviolet light. Under ultraviolet, the flowers have a darker centre, where the nectaries are located, and often specific patterns upon the petals as well. This is believed to make the flowers more attractive to pollinators such as honey bees and other insects that can see ultraviolet. This page on butterflies shows an animated comparison of black-eyed Susan (Rudbeckia hirta) flowers in visible and UV light, UV light, invisible to humans, has been referred to as bee violet, and mixtures of greenish (yellow) wavelengths (roughly 540 nm) with ultraviolet are called bee purple by analogy with purple in human vision.20


Pollination by Birds

This is not a well-observed phenomenon in the UK. However, it is proposed that the crown imperial (Fritillaria imperialis L.) is a plant pollinated by passerine birds in its native range.


Fig. 12: Blue Tit, Parus Caeruleus

In Britain, this introduced plant is visited by blue tits (Parus caeruleus L.), and bumblebees. The fit of the birds in the flower, and the geometry of the flower, strongly suggests that this plant possesses morphological adaptations to ornithophily. This is confirmed by the fact that flowers visited by blue tits are efficiently pollinated and fertilized, while those visited only by insects, or isolated from visitors, do not produce fruits. This is probably the most northerly case of ornithophily yet reported. 21


Fig. 13: Fritillaria imperialis

A further survey in 1993 by Fitzpatrick demonstrated that nectar-feeding is widespread in suburban Blue Tits, being recorded from a variety of flowers in 33 counties in the British Isles. This work also recorded that Blue Tits visited flowers of other species, such as the flowering currant, Ribes sanguineum and willows, Salix caprea and S. cinerea although their role as pollinators here was not made clear. 22


Pollination by Wind

Fig. 14: Pendulous sedge        (Credit: Fran Hitchinson/WTML)

Most species of conifers and many angiosperms, such as grasses, maples, and oaks, are pollinated by wind. Pine cones are brown and unscented, while the flowers of wind-pollinated angiosperm species are usually green, small, may have small or no petals, and produce large amounts of pollen.

Unlike the typical insect-pollinated flowers, flowers adapted to pollination by wind do not produce nectar or scent.

In wind-pollinated species, the microsporangia hang out of the flower, and, as the wind blows, the lightweight pollen is carried with it. The flowers usually emerge early in the spring before the leaves so that the leaves do not block the movement of the wind. The pollen is deposited on the exposed feathery stigma of the flower.23

Fig 15. a) These male atkins from the goat willow tree (Salix caprea) have structures that are light and feathery to better disperse and catch the wind-blown pollen.


Fig 15. b) These female atkins from the goat willow tree (Salix caprea) have structures that are light and feathery to better disperse and catch the wind-blown pollen.


By Jim Pearson





1 A third of British wild bees and hoverflies are in decline. Powney, G. D. et al: Nature Communications volume 10, Article number: 1018, 2019 https://www.nature.com/articles/s41467-019-08974-9


2. Expert reaction to the research on Britain’s pollinators: https://www.sciencemediacentre.org/expert-reaction-to-the-research-on-britains-pollinators/


3. Lumen: Boundless Biology https://courses.lumenlearning.com/boundless-biology/chapter/pollination-and-fertilization/


4. The UK bee population (2017), House of Commons Library, DEBATE PACK, No. CDP 2017/0226L, Downing, & Sutherland: https://researchbriefings.files.parliament.uk/documents/CDP-2017-0226/CDP-2017-0226.pdf


5. Pollinators: decline in numbers https://www.rhs.org.uk/advice/profile?pid=528


6. Bees: Many British pollinating insects in decline, study shows, Helen Briggs, 26 March 2019



7. New report highlights extinction threat to many of Northern Ireland’s bees https://www.buglife.org.uk/news/new-report-highlights-extinction-threat-to-many-of-northern-irelands-bees/


8. Curtin research finds introduced honeybee may pose threat to native bees (2021) https://news.curtin.edu.au/media-releases/honeybee-numbers-and-dance-skills-harmful-combination-for-native-species/


 9. Flies: the forgotten pollinators http://urbanpollinators.blogspot.com/2014/03/flies-forgotten-pollinators.html


10. Hover flies, Syrphidae https://www.bumblebee.org/invertebrates/DipteraHoverflies.htm


11 & 17: Seven insect heroes of pollination:  Natural history Museum https://www.nhm.ac.uk/discover/insect-pollination.html?gclid=CjwKCAiAs92MBhAXEiwAXTi25x_Q9AGRRqVm_7eKh3RalhLSd7qRd2TQG78gWxuLBcykmhF71dpGIRoC4sgQAvD_BwE


12. Hoverfly: https://en.wikipedia.org/wiki/Hover_fly


13. Britain's Hoverflies: A field guide - https://books.google.co.uk/books?id=EFmdBgAAQBAJ


14. All about Hoverflies Colin V Duke, BSc (Hons) http://www.microscopy-uk.org.uk/mag/indexmag.html?http://www.microscopy-uk.org.uk/mag/artmay07/cd-hoverflies.html


15. Wasps are valuable for ecosystems, economy and human health (just like bees), (2021)  Sumner, Seirian et al, UCL Centre for Biodiversity & Environment Research, UCL Biosciences https://www.ucl.ac.uk/news/2021/apr/wasps-are-valuable-ecosystems-economy-and-human-health-just-bees


16. What do wasps do? Natural History Museum: Emily Osterloff https://www.nhm.ac.uk/discover/what-do-wasps-do.html


18. Saving Butterflies and Moths: our 2021-2026 strategy: Butterfly Conservation https://butterfly-conservation.org/our-work/our-strategy


19. Moths have a secret but vital role as pollinators in the night https://www.ucl.ac.uk/news/2020/may/moths-have-secret-vital-role-pollinators-night

20. Nectar guide https://www.wikiwand.com/en/Nectar_guide

21. A Burquez. Blue tits, Parus caeruleus, as pollinators of the crown imperial, Fritillaria imperialis in Britain Oikos, vol. 55, no. 3, [Nordic Society Oikos, Wiley, 1989, pp. 335 – 340, researchgate.net https://scholar.google.com/scholar_lookup?title=Blue+tits%2C+Parus+caeruleus%2C+as+pollinators+of+the+crown+imperial%2C+Fritillaria+imperialis%2C+in+Britain.&author=Burquez+A.&publication_year=1989.


22. Nectar-feeding by suburban Blue Tits: contribution to the diet in spring. S. Fitzpatrick (1994), Bird Study, 41:2, 136-145, DOI: 10.1080/00063659409477210 https://doi.org/10.1080/00063659409477210


 23. Biology: Plant Structure and Function   Plant Reproduction, Pollination and Fertilization https://goopenct.org/courseware/lesson/199/student/?task=5


Fig: 1 An elephant hawkmoth (Deilephila elpenor) using its long proboscis to probe honeysuckle flowers (Lonicera periclymenum) after dusk https://www.nhm.ac.uk/discover/insect-pollination.html


Fig. 2: Many British pollinating insects in decline, study shows https://www.bbc.co.uk/news/science-environment-47698294


Fig. 3: Pollination Facts – What is Pollination? | Cool Kid Facts https://www.coolkidfacts.com/pollination-for-kids/


Fig. 4: Female Bombylus major in Regents Park London c © by Steven Falk. Cute and fluffy: meet the bee-flies https://www.discoverwildlife.com/animal-facts/insects-invertebrates/bee-flies/


Fig. 5: Why are hoverflies so important for our food system?



Fig. 6: Common Wasp (Vespa vulgaris) covered in pollen. © Tim Ransom. The Channel Island Pollinator Project: https://pollinatorproject.gg/wasps/

Fig. 7: Monarch butterfly; Conserve Wildlife Foundation of New Jersey http://www.conservewildlifenj.org/blog/tag/monarch-butterfly/


Fig. 8: Elephant Hawk moth: The nocturnal pollinators: scientists reveal the secret life of moths. https://butterfly-conservation.org/news-and-blog/the-nocturnal-pollinators-scientists-reveal-the-secret-life-of-moths


Fig. 9: Hummingbird hawk-moth, Macroglossum stellatarum https://www.wildlifetrusts.org/wildlife-explorer/invertebrates/moths/hummingbird-hawk-moth


Fig. 10: A rose chafer (Cetonia aurata) clambering over a pollen-laden flower © Marek Mierzejewski/ Shutterstock.com https://www.nhm.ac.uk/discover/insect-pollination.html


Fig. 11: Images of a Mimulus flower in visible light (left) and ultraviolet light (right) showing a dark nectar guide that is visible to bees but not to humans https://www.wikiwand.com/en/Nectar_guide


Fig. 12: Blue Tit, Parus Caeruleus, https://blog.lovegardenbirds.co.uk/attracting-blue-tits/


Fig. 13: Fritillaria imperialis https://www.wikiwand.com/en/Fritillaria_imperialis


Fig. 14: Pendulous sedge (Credit: Fran Hitchinson/WTML)



Fig. 15: These male (a) and female (b) catkins from the goat willow tree (Salix caprea) have structures that are light and feathery to better disperse and catch the wind-blown pollen. https://goopenct.org/courseware/lesson/199/student/?task=5