̽��ֱ�� of Cambridge - pollination

Growing wildflowers on disused urban land can damage bee health

jg533 — Tue, 15 Apr 2025 23:01:26 +0000

̽��ֱ��metals have previously been shown to damage the health of pollinators, which ingest them in nectar as they feed, leading to reduced population sizes and death. Even low nectar metal levels can have long-term effects, by affecting bees’ learning and memory - which impacts their foraging ability.

Researchers have found that common plants including white clover and bindweed, which are vital forage for pollinators in cities, can accumulate arsenic, cadmium, chromium and lead from contaminated soils.

Metal contamination is an issue in the soils of cities worldwide, with the level of contamination usually increasing with the age of a city. ̽��ֱ��metals come from a huge range of sources including cement dust and mining.

̽��ֱ��researchers say soils in cities should be tested for metals before sowing wildflowers and if necessary, polluted areas should be cleaned up before new wildflower habitats are established.

̽��ֱ��study highlights the importance of growing the right species of wildflowers to suit the soil conditions.

Reducing the risk of metal exposure is critical for the success of urban pollinator conservation schemes. ̽��ֱ��researchers say it is important to manage wildflower species that self-seed on contaminated urban land, for example by frequent mowing to limit flowering - which reduces the transfer of metals from the soil to the bees.

̽��ֱ��results are published today in the journal Ecology and Evolution.

Dr Sarah Scott in the ̽��ֱ�� of Cambridge’s Department of Zoology and first author of the report, said: “It’s really important to have wildflowers as a food source for the bees, and our results should not discourage people from planting wildflowers in towns and cities.

“We hope this study will raise awareness that soil health is also important for bee health. Before planting wildflowers in urban areas to attract bees and other pollinators, it’s important to consider the history of the land and what might be in the soil – and if necessary find out whether there’s a local soil testing and cleanup service available first.”

̽��ֱ��study was carried out in the post-industrial US city of Cleveland, Ohio, which has over 33,700 vacant lots left as people have moved away from the area. In the past, iron and steel production, oil refining and car manufacturing went on there. But any land that was previously the site of human activity may be contaminated with traces of metals.

To get their results, the researchers extracted nectar from a range of self-seeded flowering plants that commonly attract pollinating insects, found growing on disused land across the city. They tested this for the presence of arsenic, cadmium, chromium and lead. Lead was consistently found at the highest concentrations, reflecting the state of the soils in the city.

̽��ֱ��researchers found that different species of plant accumulate different amounts, and types, of the metals. Overall, the bright blue-flowered chicory plant (Cichorium intybus) accumulated the largest total metal concentration, followed by white clover (Trifolium repens), wild carrot (Daucus carota) and bindweed (Convolvulus arvensis). These plants are all vital forage for pollinators in cities - including cities in the UK - providing a consistent supply of nectar across locations and seasons.

There is growing evidence that wild pollinator populations have dropped by over 50% in the last 50 years, caused primarily by changes in land use and management across the globe. Climate change and pesticide use also play a role; overall the primary cause of decline is the loss of flower-rich habitat.

Pollinators play a vital role in food production: many plants, including apple and tomato, require pollination in order to develop fruit. Natural ‘pollination services’ are estimated to add billions of dollars to global crop productivity.

Scott said: “Climate change feels so overwhelming, but simply planting flowers in certain areas can help towards conserving pollinators, which is a realistic way for people to make a positive impact on the environment.”

̽��ֱ��research was funded primarily by the USDA National Institute of Food and Agriculture.

Reference
Scott, SB and Gardiner, MM: ‘Trace metals in nectar of important urban pollinator forage plants: A direct exposure risk to pollinators and nectar-feeding animals in cities.’ Ecology and Evolution, April 2025. DOI: 10.1002/ece3.71238

Wildflowers growing on land previously used for buildings and factories can accumulate lead, arsenic and other metal contaminants from the soil, which are consumed by pollinators as they feed, a new study has found.

Our results should not discourage people from planting wildflowers in towns and cities. But.. it’s important to consider the history of the land and what might be in the soil."

Sarah Scott

Chicory growing in a vacant lot

̽��ֱ��text in this work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Images, including our videos, are Copyright © ̽��ֱ�� of Cambridge and licensors/contributors as identified. All rights reserved. We make our image and video content available in a number of ways – on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

Yes

Licence type:

Attribution-Noncommerical

Pollinators: first global risk index for species declines and effects on humanity

fpjl2 — Mon, 16 Aug 2021 15:01:29 +0000

̽��ֱ��Global South may have most to lose from pollinator loss, with Latin America at particular risk due to crop exports and indigenous cultures.

Pollinator species vital to our food supply are under threat, warn experts

fpjl2 — Fri, 26 Feb 2016 10:20:44 +0000

Delegates from almost 100 national Governments have gathered in Kuala Lumpur to discuss how to address the threats facing animal pollinators: the bees, flies, birds, butterflies, moths, wasps, beetles and bats that transport the pollen essential to the reproduction of much of the world’s crops and plant life.

It is the first time the global community has gathered on this scale to focus on the preservation of the small species that help fertilise more than three quarters of the leading kinds of global food crops and nearly 90% of flowering wild plant species.

A report on pollinator species produced over two years by an international team of 77 scientists, including Cambridge’s Dr Lynn Dicks, has been adopted by the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) today. IPBES has 124 member Governments.

̽��ֱ��report is the first assessment ever issued by IPBES, and the first time that such an assessment has brought together multiple knowledge systems comprehensively, including scientific, and indigenous and local knowledge. It will highlight the threats to animal pollinators, and the major implications of these species’ declines for the world’s food supply and economy.

But the report also details the ways that pollinator power can be used for the benefit of biodiversity, food security and people: by harnessing natural relationships between plants and animals to improve agricultural yields and strengthen local communities.

“It is incredible to see international Governments coming together to discuss the problem of pollinators in this way,” says Lynn Dicks, from Cambridge ̽��ֱ��’s Department of Zoology.

“Without pollinators, many of us would not be able to enjoy chocolate, coffee and vanilla ice cream, or healthy foods like blueberries and brazil nuts. ̽��ֱ��value of pollinators goes way beyond this. People’s livelihoods and culture are intimately linked with pollinators around the world. All the major world religions have sacred passages that mention bees.”

̽��ֱ��volume of pollinator-dependent food produced has increased by 300% over the past 50 years, including most fruits from apple to avocado, as well as coffee, cocoa, and nuts such as cashews. This shows an increasing dependence of agriculture on pollinators.

Such crops now occupy around 35% of all agricultural land. While these crops rely on animal pollination to varying degrees – along with, for example, wind-blown pollination – the scientists estimate that between 5 and 8% of all global crop production is directly attributable to animal pollinators, with an annual market value that may be as much as 577 billion US dollars.

However, the experts warn that a variety of agricultural practices are contributing to steep declines in key pollinating species across Europe and North America. In Europe, populations are declining for at least 37% of bee and 31% of butterfly species.

A lack of data for Africa, Latin America and Asia means we are currently in the dark about the status of pollinators in many parts of the world, say the scientists. Where national ‘red lists’ are available, they show that up to 50% of global bee species, for example, may be threatened with extinction.

For some crops, including cocoa, wild pollinators contribute more to global crop production than managed honey bees. Wild bee populations are of particular concern, as bees are “dominant” pollinators, say scientists, and visit over 90% of the leading global crop types.

Changes in land-use and habitat destruction are key drivers of pollinator decline. Increasing crop monocultures – where the same plant is homogenously grown across vast swathes of land – mean that the plant diversity required by many pollinators is dwindling.

Increased use of pesticides are a big problem for many species – insecticides such as neonicotinoids have been shown to harm the survival of wild bees, for example – and climate change is shifting seasonal activities of key pollinators, the full effects of which may not be apparent for several decades.

̽��ֱ��decline of practices based on indigenous and local knowledge also threatens pollinators. These practices include traditional farming systems, maintenance of diverse landscapes and gardens, kinship relationships that protect specific pollinators, and cultures and languages that are connected to pollinators.

Everyone should think carefully about whether they need to use insecticides and herbicides in their own gardens

Many livelihoods across the world depend on pollinating animals, say scientists. Pollinator-dependent crops include leading export products in developing countries (such as coffee and cocoa) and developed countries (such as almonds), providing employment and income for millions of people.

If the worst-case scenario – a complete loss of animal pollinators – occurred, not only would between 5 and 8% of the world’s food production be wiped out, it would lower the availability of crops and wild plants that provide essential micronutrients to human diets, risking vastly increased numbers of people suffering from Vitamin A, iron and folate deficiency.

However, the assessment says that by deploying strategies for supporting pollinators, we could not only preserve the volume of food they help us produce, but we could boost populations and in doing so could even improve production in sustainable farming systems, so-called “ecological intensification”.

Many pollinator-friendly strategies are relatively straightforward. Maintaining patches of semi-natural habitats throughout productive agricultural land would provide nesting and ‘floral resources’ for many pollinators. This could be as simple as strips of wild flowers breaking up crop monocultures, for example, and identifying and tending to nest trees in farming settings.

Certain traditional crop rotation practices using seasonal indicators such as flowering to trigger planting also help to maintain diversity – and it is diversity that is at the heart of flourishing pollinator populations.

There are actions that Governments around the world could take, says Dr Dicks, such as raising the standards of pesticide and GMO risk assessment, or supporting training for farmers in how to manage pollination and reduce pesticide use. National-level monitoring of wild pollinators, especially bees, would help to address the lack of long term data on pollinator numbers.

“There are many things individual people can do to help pollinators, and safeguard them for the future,” says Dr Dicks.

“Planting flowers that pollinators use for food, or looking after their habitats in urban and rural areas, will help. Everyone should also think carefully about whether they need to use insecticides and herbicides in their own gardens.”

More information about how to help wild pollinators can be found at the Bees Needs website, which is part of the National Pollinator Strategy for England.

Inset image: Lynn Dicks at the IPBES meeting in Kuala Lumpur.

A new report from experts and Government around the world addresses threats to animal pollinators such as bees, birds and bats that are vital to more than three-quarters of the world’s food crops, and intimately linked to human nutrition, culture and millions of livelihoods. Scientists say simple strategies could harness pollinator power to boost agricultural yield.

People’s livelihoods and culture are intimately linked with pollinators around the world. All the major world religions have sacred passages that mention bees

Lynn Dicks

Dino J. Martins/Nature Kenya

Carpenter bee (Xylocopa flavorufa) visiting coffee flower (Coffea arabica)

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Flowers tone down the iridescence of their petals and avoid confusing bees

jeh98 — Thu, 25 Feb 2016 17:04:02 +0000

Iridescent flowers are never as dramatically rainbow-coloured as iridescent beetles, birds or fish, but their petals produce the perfect signal for bees, according to a new study published today in Current Biology.

Bees buzzing around a garden, looking for nectar, need to be able to spot flower petals and recognise which coloured flowers are full of food for them. Professor Beverley Glover from the ̽��ֱ�� of Cambridge’s Department of Plant Sciences and Dr Heather Whitney from the ̽��ֱ�� of Bristol found that iridescence – the shiny, colour-shifting effect seen on soap bubbles – makes flower petals more obvious to bees, but that too much iridescence confuses bees’ ability to distinguish colours.

Whitney, Glover and their colleagues found that flowers use more subtle, or imperfect, iridescence on their petals, which doesn’t interfere with the bees’ ability to distinguish subtly different colours, such as different shades of purple. Perfect iridescence, for example as found on the back of a CD, would make it more difficult for bees to distinguish between subtle colour variations and cause them to make mistakes in their flower choices.

“In 2009 we showed that some flowers can be iridescent and that bees can see that iridescence, but since then we have wondered why floral iridescence is so much less striking than other examples of iridescence in nature,” says Glover. “We have now discovered that floral iridescence is a trade-off that makes flower detection by bumblebees easier, but won’t interfere with their ability to recognise different colours.”

Bees use ‘search images’, based on previously-visited flowers, to remember which coloured flowers are a good source of nectar.

“On each foraging trip a bee will usually retain a single search image of a particular type of flower,” explains Glover, “so if they find a blue flower that is rich in nectar, they will then visit more blue flowers on that trip rather than hopping between different colours. If you watch a bee on a lavender plant, for example, you’ll see it visit lots of lavender flowers and then fly away – it won’t usually move from a lavender flower to a yellow or red flower.”

This colour recognition is vital for both the bees and the plants, which rely on the bees to pollinate them. If petals were perfectly iridescent, then bees could struggle to identify and recognise which colours are worthwhile visiting for nectar – instead, flowers have developed an iridescence signal that allows them to talk to bees in their own visual language.

̽��ֱ��researchers created replica flowers that were either perfectly iridescent (using a cast of the back of a CD), imperfectly iridescent (using casts of natural flowers), or non-iridescent. They then tested how long it took for individual bees to find the flowers.

They found that the bees were much quicker to locate the iridescent flowers than the non-iridescent flowers, but it didn’t make a difference whether the flowers were perfectly or imperfectly iridescent. ̽��ֱ��bees were just as quick to find the replicas modelled on natural petals as they were to find the perfectly iridescent replicas.

When they tested how fast the bees were to find nectar-rich flowers amongst other, similarly-coloured flowers, they found that perfect iridescence impeded the bees’ ability to distinguish between the flowers – the bees were often confused and visited the similarly-coloured flowers that contained no nectar. However, imperfect iridescence, found on natural petals, didn’t interfere with this ability, and the bees were able to successfully locate the correct flowers that were full of nectar.

“Bees are careful shoppers in the floral supermarket, and floral advertising has to tread a fine line between dazzling its customers and being recognisable,” says Lars Chittka from Queen Mary ̽��ֱ�� of London, another co-author of the study.

“To our eyes most iridescent flowers don’t look particularly striking, and we had wondered whether this is simply because flowers aren’t very good at producing iridescence,” says Glover. “But we are not the intended target – bees are, and they see the world differently from humans.”

“There are lots of optical effects in nature that we don’t yet understand. We tend to assume that colour is used for either camouflage or sexual signalling, but we are finding out that animals and plants have a lot more to say to the world and to each other.”

Glover and her colleagues are now working towards developing real flowers that vary in their amount of iridescence so that they can examine how bees interact with them.

“ ̽��ֱ��diffraction grating that the flowers produce is not as perfectly regular as those we can produce on things like CDs, but this 'advantageous imperfection' appears to benefit the flower-bee interaction,” says Whitney.

Reference: Whitney, Heather et al “Flower Iridescence Increases Object Detection in the Insect Visual System without Compromising Object Identity” Current Biology (2016). DOI: https://dx.doi.org/10.1016/j.cub.2016.01.026

Professor Glover will be giving the talk 'Can we improve crop pollination by breeding better flowers?' at the Cambridge Science Festival on Sunday 20 March 2016. More information can be found here: http://www.sciencefestival.cam.ac.uk/events/can-we-improve-crop-pollinat...

Inset images: Iridescent flower (Copyright Howard Rice); Bee on non-iridescent flower (Edwige Moyroud); Bee on non-iridescent flower (Edwige Moyroud).

Latest research shows that flowers’ iridescent petals, which may look plain to human eyes, are perfectly tailored to a bee’s-eye-view.

There are lots of optical effects in nature that we don’t yet understand... we are finding out that animals and plants have a lot more to say to the world and to each other

Beverley Glover

Bee on a non-iridescent flower

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

̽��ֱ��Life and Death of the Queen Bumblebee

amb206 — Wed, 23 Sep 2015 09:43:16 +0000

Scroll to the end of the article to listen to the podcast.

Each autumn, colonies of bumblebees die. All, that is, apart from the gravid (egg-carrying) queens who survive the winter in tiny burrows in the ground. Early in the spring, the queen emerges to start making a nest in which to lay her eggs. To do so, she needs the energy provided by nectar and pollen. If she can’t find enough flowers from which to gather these resources, she will die – and the next generation she is carrying will die too.

Bumblebees are among the UK’s estimated 1,500 species of wild pollinators and play a vital role in the environment. They transfer pollen from plant to plant – and thus ensure that plants reproduce. An estimated 75% of the crops we eat depend on pollination. Bumblebees are particularly important pollinators of beans, raspberries and tomatoes. Uniquely, they are capable of ‘buzz pollination’, producing a high-pitched buzz which releases pollen from pollen-containing tubes inside some flowers. Tomatoes are pollinated like this.

Over the past 80 years or so, there has been a dramatic decline in the distributions of some bumblebee species. Two of the 26 species of bumblebee once common in the UK are now extinct. Scientists think that the factors behind this decline are several and interconnected. Most obvious is the loss of wild flower meadows which have disappeared as farming has become more intensive and fields made larger by the removal of hedgerows. Although many British gardens burst with flowers, many of the showy favourites (such as pansies and begonias) produce little pollen or nectar.

A recent report by Dr Lynn Dicks (Department of Zoology) and staff at Natural England makes an important contribution to the development of nation-wide strategies to halt – and reverse – the loss of wild pollinators such as bumblebees. In 2013, a rare and time-limited opportunity opened up for scientists to contribute to the development of an ‘agri-environment package’ for wild pollinators as part of the new Countryside Stewardship scheme, launched earlier this year.

As an expert in the ecology of flower-visiting insects, Dicks used this ‘policy window’ to bring together a wide range of available information and ask key questions about wild pollinators and their relationship with the farmed environment. In providing tentative answers to these questions, her paper provides ballpark figures on aspects of land management that determine population levels of wild pollinators, including bumblebees, and bolsters arguments for policies that encourage farmers to sow a mix of wild flowers.

“An agri-environment package is a bundle of management options that supply sufficient resources to support a target group of species. Data from a similar package, aimed at helping farmers provide resources for species of birds known to be declining, are not yet publically available. But some of the measures in the package are known to have led to an upturn in numbers of six target species – including skylarks and yellowhammers – which is most encouraging,” says Dicks.

“We depend on pollinators for food production so it’s in our interests to halt drops in numbers. If species are declining, it’s because they lack specific resources – or because other factors are reducing their numbers faster than they can reproduce. Some risks to pollinators – notably pesticides and climate change – are difficult to quantify and politically challenging. An alternative is to focus policy on providing the resources that are lacking – such as nectar-rich flowers.”

̽��ֱ��most critical period for bumblebee survival is March and April when the queens that have hibernated over the winter need access to enough nectar and pollen to raise their first batch of workers within an estimated 1km radius of their nests. ̽��ֱ��first batch of eggs laid by the queen become female workers whose role is to feed the new colony by visiting flowers to gather nectar. Throughout the summer the queen will produce further batches of eggs, seldom leaving the nest. She will eventually control a nest of as many as 400 individuals, including new queens. Honeybee hives, in comparison, typically contain around 50,000 bees.

Many commercial crops flower several weeks after the queen bumblebees are most in need of nectar. Oil seed rape, for example, produces its bright yellow flowers in May and June. Nectar and pollen provided by these crops are valuable to later batches of bumblebees. However, the first batch of bumblebees relies on plants that flower in early spring – including those associated with rough land (such as comfrey and white deadnettle) and hedgerow species (such as willow, hawthorn and blackthorn).

Recent research revealed that wild pollinators provide a much more important service to commercial crops than previously thought. Dicks’ report identifies opportunities for enhancing the environment for six species of wild bee including three species of bumblebee by sowing wild flowers and providing environments for nests.

She compiled and analysed data from a number of wildlife conservation and research organisations, including the Bumblebee Conservation Trust, to build an overall picture of the resources that these insects need to flourish.

By calculating the pollen demands of individual bees, and the resulting demand for flowers, Dicks has come up with some approximate figures in terms of the percentage of land and hedgerow needed to resource a healthy population of selected wild pollinators. Using a 100-hectare block of land as the basis for calculations, she estimates that the provision of a 2% flower-rich habitat and 1km flowering hedgerow will supply the six pollinator species with enough pollen to feed their larvae.

“We suggest that farmers sow headlands, field corners and other areas with mixes that will flower in the summer months, but they also need to manage hedgerows, woodland edges, margins and verges to enhance early and late flowering species and provide nesting and hibernating opportunities,” says Dicks. “It’s really important that the packages offered to farmers through the Countryside Stewardship scheme are easy to implement and well supported by financial incentives and advice. Because we are learning more all the time about the interaction between wild pollinators and the environment, schemes also need to have built-in flexibility.”

Next in the Cambridge Animal Alphabet: R is for an animal that is often found among the pages of children's literature.

Have you missed the series so far? Catch up on Medium here.

Inset images: Bombus pascuorum (Joan Chaplin); Bombus lapidarius (Tessa Bramall).

The Cambridge Animal Alphabet series celebrates Cambridge's connections with animals through literature, art, science and society. Here, Q is for Queen Bumblebee, one of the UK's 1,500 species of wild pollinators that play a vital role in the environment and food production.

We depend on pollinators for food production so it’s in our interests to halt drops in numbers

Lynn Dicks

Linda Peall

Bombus pascuorum

̽��ֱ��text in this work is licensed under a Creative Commons Attribution 4.0 International License. For image use please see separate credits above.

Yes

Licence type:

Attribution

Why buttercups reflect yellow on chins

gm349 — Wed, 14 Dec 2011 08:00:54 +0000

Scientists have found that the distinctive glossiness of the buttercup flower (Ranunculus repens), which children like to shine under the chin to test whether their friends like butter, is related to its unique anatomical structure. Their findings were published today, 14 December, in the Royal Society journal Interface.

̽��ֱ��researchers discovered that the buttercup petal’s unique bright and glossy appearance is the result of the interplay between its different layers. In particular, the strong yellow reflection responsible for the chin illumination is mainly due to the epidermal layer of the petal that reflects yellow light with an intensity that is comparable to glass.

Scientists have been interested in how the buttercup flower works for over a century. They have previously shown that the reflected colour is yellow due to the absorption of the colours in the blue-green region of the spectrum by the carotenoid pigment in the petals. As the blue-green light is absorbed, the light in the other spectral regions (in this case, primarily yellow) is reflected. It has also been known for many years that the epidermal layer of the petals is composed of very flat cells, providing strong reflection.

This new study shows how the buttercup’s exceptionally bright appearance is a result of a special feature of the petal structure. ̽��ֱ��epidermal layer of cells has not one but two extremely flat surfaces from which light is reflected. One is the top of the cells, the other exists because the epidermis is separated from the lower layers of the petal by an air gap. Reflection of light by the smooth surface of the cells and by the air layer effectively doubles the gloss of the petal, explaining why buttercups are so much better at reflecting light under your chin than any other flower.

̽��ֱ��researchers, who were funded by the Leverhulme Trust and the EPSRC, also found that the buttercup reflects a significant amount of UV light. As many pollinators, including bees, have eyes sensitive in the UV region, this provides insight into how the buttercup uses its unique appearance to attract insects.

Dr Silvia Vignolini, from the ̽��ֱ�� of Cambridge’s Department of Physics (Cavendish Laboratory), explained the importance of the buttercup’s unique appearance: “Although many different factors, such as scent and temperature, influence the relationships between pollinators and flowers, the visual appearance of flowers is one of the most important factors in this communication. Flowers develop brilliant colour, or additional cues, such as glossiness - in the case of the buttercup - that contribute to make the optical response of the flower unique. Moreover, the glossiness might also mimic the presence of nectar droplets on the petals, making them that much more attractive.”

Dr Beverley Glover, Department of Plant Sciences, said: “This phenomenon has intrigued scientists and laymen alike for centuries. Our research provides exciting insight into not only a children’s game but also into the lengths to which flowers will go to attract pollinators.”

Professor Ulli Steiner, from the Nanophotonics Centre at the Cavendish Laboratory, the ̽��ֱ�� of Cambridge’s Department of Physics, said: “It is fun to revisit a problem that is more than one century old and, using modern methods, discover something new. ̽��ֱ��strong collaboration between Physics and the Plant Sciences has enabled this.”

Scientists discover why buttercups reflect yellow on chins – and it doesn’t have anything to do with whether you like butter. ̽��ֱ��new research sheds light on children’s game and provides insight into pollination.

Our research provides exciting insight into not only a children’s game but also into the lengths to which flowers will go to attract pollinators.

Dr Beverley Glover, Department of Plant Sciences

Photo Silvia Vignolini

Buttercup under chin

This work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page.

Yes