See no weevil, hear no weevil

By Athayde Tonhasca

As the story goes, J.B.S. Haldane (1892-1964), British/Indian geneticist, evolutionary biologist and mathematician, found himself in the company of a group of theologians. On being asked what one could learn about The Creator from studying his creation, the atheist Haldane is said to have answered ‘an inordinate fondness for beetles.’ Haldane may have said something like that, and indeed a Great Architect of the Universe would have had to be partial to the order Coleoptera. With nearly 400,000 known species, beetles lead the biodiversity table, making up about 25% of all known animal species. But if the Almighty Creator liked beetles, he was especially fond of weevils (superfamily Curculionoidea): there are over 97,000 described species, of which 76,761 are snout beetles (family Curculionidae) (Global Biodiversity Information Facility). But we know these figures are gross underestimations because in poorly studied areas, i.e., most of the world, the majority of weevil specimens collected are from unknown species.

A circular tree of life for some described eukaryote groups (all organisms except bacteria and bacteria-like Archaea). Insects – in the left column – make up about 63% of the total. Vertebrates, together with other deuterostomes (animals for which the anus is formed before the mouth during embryonic development) are a mere ‘etcetera’ in the big scheme of life. Their biodiversity is comparable to weevils’ © Adam Dent, Wikimedia Commons.

Weevils are found practically everywhere, and almost all of them are plant eaters. They feed on plants from any terrestrial or freshwater habitats and on a range of tissues: roots, stems, phloem, fruits, flowers or seeds. Many species are among the most damaging pests of stored grain, field crops, orchards, ornamental plants and commercial forests. Weevils’ destructive potential can’t be overestimated. The boll weevil (Anthonomus grandis) wrecked the American cotton industry in the 1920s and 30s, then invaded South America in the 80s for further mayhem. In the US, the Southern pine beetle (Dendroctonus frontalis) is able to wipe out thousands of hectares of pine in less than two years, while grain weevils (Sitophilus spp.) can completely destroy rice, maize, wheat, oats, and many other products stored is silos around the world. You may have had your own experience with weevils infesting a bag of flour or a box of pasta in your pantry.

Rice weevils (S. oryzae), a pest of stored grains and cereal products. Some weevils don’t have the long snout characteristic of the group, and not all long-snouted beetles are weevils © CSIRO, Wikimedia Commons.

Considering weevils’ charge sheet, we would be tempted to dump the lot in the ‘creepy crawlers’ category. But that would be hasty and unjustified. Only a tiny minority of weevils are harmful, while the great majority contribute to the functioning of ecosystems. One way they do this is by pollinating a range of plants.

Cantharophily (from the Greek word kántharos for beetle), or pollination by beetles, is not well understood or researched, despite being one of the first pollinating systems in the evolutionary history of flowering plants. With time, bees, flies and moths became the main pollinators, but many plants, especially of ancient lineages such as magnolias (Magnoliaceae), retained cantharophily. Some custard apple-related plants (Annonaceae), arums (Araceae), palms (Arecaceae) and orchids (Orchidaceae) are also pollinated by beetles.

Most beetles don’t handle pollination skilfully and gently: they plough through flowers, gobbling down nectar, pollen or petals, defecating as they go, often spilling more pollen than they eat – that’s why they are called ‘mess and soil’ pollinators. During these raids, beetles become contaminated with pollen grains, which are deposited on the next plant they visit. Weevils, however, have a more intimate and nuanced rapport with their hosts. They lay their eggs on the flowers, where their larvae will grow and mature by feeding on pollen, ovules, or other floral parts. By hosting weevils during a significant portion of their lives, plants are almost guaranteed being pollinated for the price of a fraction of their reproductive parts. 

This type of mutualistic relationship is known as brood-site pollination or nursery pollination and it has been reported dozens of times for different groups of insects, mostly in the tropics; the interactions between figs and wasps and between yuccas and moths are two of the better known examples. In the case of weevils, hundreds of species have coevolved brood-site associations with a range of plants, but mostly with palms (family Arecaceae). 

Pupa (A), egg (B) and larvae (C-F) of weevils growing in different inflorescence parts of palms. Credits: A, F: J. Haran, B-E: B. de Medeiros © Haran et al., 2023.

One instance of weevil-palm mutualism has particular relevance for its ecological and economic implications: the pollination of African oil palm (Elaeis guineensis) by the African oil palm weevil (Elaeidobius kamerunicus). Male weevils feed on the palm’s flowers and pollen, while females oviposit in the flower structures, in which the larvae feed and develop. You can watch the weevils in action.

When oil palm growers around the world, but mostly in Indonesia and Malaysia (the leading producers and exporters of palm oil), began to import the pollinating weevil in 1981, the industry changed radically. The beetle adapted well to its new habitats and boosted African oil palm pollination, which resulted in sharp increases in production, revenue and applications; palm oil made its way into margarines, chocolates, baked products, cooking oils, soap, detergents, cosmetics – you name it. The “million dollar weevil” had been found (Robins, 2021). 

A female African oil palm weevil, and weevils clustering on palm flowers © Ken Walker, Museum Victoria, CABI (L) and Susenoqurnia, Wikimedia Commons.

But as sociologist Robert K. Merton warned us, purposeful actions are bound to have multiple outcomes, some of them unanticipated. This law of unintended consequences (flippantly identified as Murphy’s Law) suited the case of the million dollar weevil to a T. Large-scale oil palm production resulted in massive deforestation that is destroying the habitats of large numbers of plant and animal species, and increased levels of erosion and pollution.

Fortunately, the introduced African oil palm weevil is an isolated case of ecological mishap. All other known examples of beetle brood-site pollination are mutualisms that help maintain biodiversity. Seres & Ramirez (1995) estimated that more than 45% of palms and herbs in some cloud forests are beetle‐pollinated, and Haran et al. (2023) have recorded at least 600 cases or suspected cases of palm-weevil interactions: the true number is likely to be much larger. We have the vaguest understanding of the pollinating services played by these weevils, but it mustn’t be something to sniff at considering that the number of Curculionidae species alone is almost four times bigger than the number of bee species (~20,000). 

Palms and many other types of plant pollinated by weevils are sources of food, building materials, cosmetics and medicines; a good portion of those products are consumed locally or sold abroad, generating much needed income to developing countries. Not so bad for those maligned big-conked characters.   

According to biblical sources, Noah’s ark had ~42,500 m³ of available space, the equivalent of 570 standard railroad stock cars. We can deduce that Noah’s ship was not a run-of-the-mill zoo because most species competing for a berth comprised parasites and weevils. Art by Simon de Myle, 1570. Wikimedia Commons.

Celebrating Park Life

If you know your music, you will know that the successful Britpop band Blur have been gearing up to celebrate the 30th anniversary of their ParkLife album. Whilst their version of Park Life caught the imagination back in 1994, there is no doubt that today we are as likely to associate Park Life with pollinator actions as we are music. 

This was brought sharply into focus at the latest meeting of the Park Managers Forum run by the urban greenspace charity greenspace scotland held on Midsummer’s Day 2023 in Falkirk. The theme was ‘nature restoration in urban greenspace’. 

NatureScot were delighted to offer funding support and grateful that the team at greenspace scotland and Falkirk Council brought together 14 councils’ staff from a range of greenspace and planning specialisms to look at issues including  the challenges of naturalising amenity grass and promoting nature restoration in a public park setting.

So, what were the highlights? 

The Falkirk team had laid on a series of visits to illustrate particular talking points. At Camelon, which lies to the west of Falkirk, there was an opportunity to look at sustainable grass management on road verges and parks and see what was involved in wet meadow creation. 

A constant in the Camelon discussions was the value of relaxed mowing.

At the intriguingly named Policy Bing, visitors were invited to take a closer look at nature restoration in an urban open space, and consider areas where previously industrial and derelict land had been enhanced for access and recreation alongside nature. 

The evidence gleaned from viewing this site is that partnerships and shared objectives make it possible to reclaim heavily degraded land to improve the environmental quality of our towns.

Over at ever-popular Callendar Park, the story was one of discussing what could follow on a site where nature enhancements are already happening. Colleagues were invited to share ideas on future use/enhancement of the old golf course area. 

This transformation desire has echoes of what happened at Fernbrae Meadows in South Lanarkshire, where the Blairbeth Golf Course was transformed into an urban park following support from Scotland’s Green Infrastructure Fund.

Ian Robertson of greenspace scotland was instrumental in organising the day. He gathered some comments across the day and noted a few things of interest. 

“One thing that cropped up was the scale of arisings – material that is cut and needs to be removed to sustain new habitats – in this kind of work. There are significant issues around disposal and the associated costs. As local authorities increase the amount of naturalised grassland in their estate, this is an issue that will have to be addressed. And how far will local authorities be able to generalise an approach to disposal of arisings, versus needing to take a site-by-site approach?”

Scaling up nature restoration work of this kind will likely also mean new or more equipment is needed. And some participants in the discussions thought there is merit in, or scope for, large-scale joint composting disposal schemes between local authorities.

“Communicating what is happening was viewed as important too. In dealing with arisings a local authority might opt to create an onsite disposal or ‘rotting down’ area. One view is that this is best practice, and that it minimises carbon footprint and cash costs. Yet people reported that some residents see this as untidy or akin to a form of fly-tipping, so there is a job to explain what is happening.” 

 “That same issue of perception applies to some places where a relaxed grassland maintenance regime is in place, because at the end of the growing season (and before the cut-and-lift exercise) things can look a bit unkempt to some eyes. Again there is a job to raise awareness of the benefits of these areas for wildlife.

“On that same theme, in more than one council naturalisation has caused debate around perceptions of a neglected space and negative impacts for well-being and safety. One answer is to have some short grass ‘frame’ relaxed or naturalised grassland management. 

“In other places, some people were reported as feeling and voicing a loss of open space – people felt they were losing an amenity – for example areas to walk dogs and to play ball games. So Councils are finding out that naturalisation won’t be for every urban greenspace.” 

In related examples to the work in Falkirk, Aberdeen City Council is extending naturalised greenspace management by improving and creating blue/green habitats in two high profile parks in the city. Under the banner ‘Aberdeen Flagship Parks for Pollinators’, Duthie Park beside the River Dee and Seaton Park on the River Don have been chosen to show how this approach can benefit both people and wildlife.  The parks also serve more deprived areas of the city, include extensive areas of traditional horticultural layouts, and are heavily used. The project was awarded Scottish Government Nature Restoration in Parks funding, part of the Scottish allocation of the Levelling Up Parks Fund provided by the UK Government. The fund is being managed by greenspace scotland on behalf of the Scottish Government. 

What were the take home messages that proved most pressing on the Falkirk day?

Many local authorities and their staff are working strenuously on the nature restoration and biodiversity agendas and are keen to progress changes. There are challenges, particularly around resourcing, along the way. It’s about finding solutions for specific sites that will be sustainable in terms both of management regimes and financially. It is crucial too that they have community support.

There is a strong desire to accelerate nature restoration work in multiuse parks and urban greenspaces. What is being achieved in the likes of Falkirk and Aberdeen shows the potential to connect such work, with benefits for nature and people.

With many thanks to Ian M Robertson (greenspace scotland), Programme Manager at the Park Managers Forum.

Find out more:

Park Managers Forum – June 2023

Aberdeen Flagship Parks for Pollinators

Greenspace Scotland

Hot matchmakings

By Athayde Tonhasca

One day in December 1735, Robert Marsham, Esquire, heard a thrush singing on one of the family estates in Stratton Strawless, Norfolk, and had a thought: would the timing of thrush singing vary with seasonal conditions? Marsham figured that the onset of spring would be a good point of reference to test his idea, so in the following year he recorded the arrival date of the first swallow (Margary, 1925). Soon Marsham had a list of 27 ‘Indicators of Spring’ such as the first sightings of butterflies, first call of the cuckoo, first appearance of snowdrop flowers, sycamore leaves, hawthorn blossoms, and the sprouting of turnip, which was an essential crop for Norfolk farmers. A committed and meticulous nature observer, Marsham carried on recording year after year, and presented his observations to the Royal Society in 1779 (he was elected Fellow in the following year). After Marsham death, his family carried on recording until the death of Mary Marsham, Robert’s great-great-great-granddaughter, in 1958.

Marsham would undoubtedly be pleased to know that his work inspired the creation of a network of amateur naturalists who were enthusiastic about recording seasonal markers. And unbeknownst to all of them, they were the forerunners of a discipline now known as phenology: from the Greek phenos (appearance) and logos (study), it investigates the effects of the seasons and climate on recurring natural phenomena. Today, the UK Phenology Network, sponsored by the Woodland Trust, hosts Nature’s Calendar, a database with over 2.9 million records of phenological events.

Robert Marsham, FRS (1708-1797), a phenology pioneer © National Trust Collections, Wikimedia Commons.

For some species, life cycle occurrences are triggered by the onset of rainfall, or by a day-length threshold (photoperiod); genetics also plays a role. But the great seasonal regulator is temperature, which affects so much of organisms’ activity and metabolism. As we gloomily contemplate entering the anthropocene, with more and more signs that life and Earth’s vital cycles are being affected by human activity and rising temperatures, phenology has never been more relevant. In Britain, first flowering has advanced an average of 5.4 days every ten years between 1952 and 2019, accelerating to almost one month since 1986 (Büntgen et al., 2022). Other studies in North America and continental Europe have shown similar results. These temporal shifts can have many consequences because plant seasonality influences the abundance and distribution of herbivores and their consumers, ecosystem services, and cycles of water and carbon. People too are directly affected, as phenology dictates crop planting, fertilizing and harvesting, and the production of allergy-triggering pollen.

First flowering dates between 1753 and 2019. There is a difference of 26 days between older (1753–1986) and recent (1987–2019) dates © Büntgen et al., 2022.

Unsurprisingly, poikilothermic (‘cold blooded’) animals – those whose internal temperature is directly affected by environmental temperature such as invertebrates, reptiles and amphibians – are particularly sensitive to climatic variations. For insects, a warmer planet has some perks: diapause (the period of suspended development) will terminate earlier, winter mortality will be lower, spring will come sooner and summers will last longer. Most insects will have more time for developing and dispersing – including crop and forestry pests, whose outbreaks are becoming more frequent and serious. Nasties such as disease-carrying mosquitoes are also benefiting from rising temperatures.

While some insects bask in a cosy warmer world, others show signs of approaching their thermal limits because they are upping sticks. In the northern hemisphere, the distribution and abundance of many butterflies, beetles, dragonflies and grasshoppers have moved northwards or upwards in mountainous areas. Bees, which are largely poikilothermic (species like bumble bees generate some internal heat) inevitably have also been caught in the great calendar shift. Museum data from specimens collected since the 1880s indicated that the flight period of 10 bee species from northeastern North America has advanced 10.4 days on average (Bartomeus et al., 2011); in the UK, 40 years of records revealed that the average emergence dates of 88 bee species has moved forward at a pace of 0.40 days/year since 1980, or 6.5 days/1°C warming (Wyver et al., 2023). Other studies add to the list of incriminating evidence.

Change in UK bees’ emergence dates per °C temperature increase. Error bars are standard errors © Wyver et al., 2023.

These developments don’t bode well for pollination services. If plants’ and pollinators’ phenologies change at different rates or magnitudes, they may become out of sync. For flowers, there could be fewer visitations and pollen deposition; for pollinators, there could be less nectar and pollen. Fortunately, most pollinators visit multiple plant species, and plants are visited by multiple pollinators. This flexibility may explain why we don’t know of any case of pollination failure because of life cycle asynchronies. 

Some plant-pollinator systems show remarkable adaptability. A population of orange-legged furrow bees (Halictus rubicundus) in the American state of Utah was monitored daily for 22 years for the detection of the first day of nesting and its possible relation with the environment. It turned out that time of nesting varied widely (a range of 44 days), but temperature was a much better predictor than calendar date (Cane, 2021). Crucially, blooming and bees’ activity in the surrounding area remained roughly synchronised: apparently, plants and bees are responding to the same environmental cues. Similar results were obtained from long-term observations (12 to 14 years) for the Eastern cucurbit bee (Peponapis pruinosa), the South-eastern blueberry bee (Habropoda laboriosa) and the tawny mining bee (Andrena fulva), a common British species.

A female orange-legged furrow bee. This species, widely distributed throughout the northern hemisphere, seem to be coping well with a changing world © linsepatron, Wikimedia Commons.

However, things could change if phenologies are pushed even further apart, and experimentation has shown that this risk is quite real. Schenk et al. (2017) simulated plant-bee mismatching by manipulating the availability of flowers to caged Osmia bicornis, O. brevicornis and O. cornuta, mason bees valued as crop pollinators. The results: a misalliance of a mere six days significantly reduced bees’ activity and reproduction. Slominski & Burkle (2021) used similar methodology in a study with O. cornifrons and observed that bees’ visitation to flowers and the weight of their offspring decreased with increased asynchrony, measured in days.

Flight cages used to simulate asynchronous supply of blossoms to mason bees © Schenk et al., 2017.

And there is more to warming than mismatched life events. Under high temperatures, some pollinators may forage only during early mornings and over shorter distances to avoid heat stress. Consequently, flowers that open later in the day could be less visited, and some not visited at all. Pollinators may end up with fewer options because warmer, drier summers reduce flowering periods or intensity. Some plants may be missed altogether: pollinators find flowers by picking up their chemical signatures in the air, and if the heat alters the chemical composition of these scents, they may no longer be recognised by pollinators.

These scenarios are not wild speculations, but possibilities grounded in research. We cannot predict specific climate-induced effects on pollinators and plant species because of our poor understanding of the processes and variables involved, let alone the fact that responses have been far from uniform. For example, few cases of local extinctions can be attributed to anthropogenic climate warming (Cahill et al., 2013). What we can say is that phenologies out of kilter may have disagreeable repercussions.

We all feel overwhelmed and perhaps a bit wary of climatic bad news; but pollinators and pollination services deserve to be considered in any plan to sort out the muddle we’ve got ourselves in.

The optimism of 1912: the influence of carbon emissions in global temperatures could be felt “in a few centuries” © Popular Mechanics, Wikimedia Commons.

More than history

Just as NatureScot works to improve Scotland’s natural environment, so Historic Environment Scotland is the government agency tasked with caring for and promoting Scotland’s historic environment. However, they do much more besides, and with a strong Climate Action Plan they increasingly make space for our hard-pressed pollinators.

Historic Environment Scotland (HES) has a fascinating remit. They look after a suite of properties of national importance, care for many of Scotland’s major ancient monuments, and in addition are involved with a range of archaeological works.  Where their work most notably crosses over with NatureScot’s remit is in their contribution to the Scottish Government’s strategy to tackle climate change and reduce Scotland’s carbon footprint.

Given that a key aim of the Pollinator Strategy for Scotland is that by 2027 there will be a strong network of good quality pollinator habitats in place they are a valuable partner in driving things forward.  With a suite of over 300 properties, often with green spaces attached, they are well placed to help our hard-pressed pollinators. What’s more they work with a range of private landowners so are particularly adept at liaising with others to achieve their goals.

Charlie Hawkins, Biodiversity and Climate Change coordinator at HES, leads on this work. An appreciation of the challenges facing nature lies close to his heart. He knows that within the suite of Historic Environment Scotland properties are many opportunities to make changes and introduce management regimes which are helpful to nature.

At Holyrood Park, the Ranger Service has long worked on ensuring areas of the park can support pollinators. Adjacent to Queen’s Drive, for example, there is a wildflower area comprised of yellow rattle, yarrow, harebells, and white campion, among many other species. In 2023, this area was strengthened through collaboration between the Holyrood Park Grounds Staff, and volunteers. Between them they grew and planted 1,500 wildflower plants from seed to further benefit pollinators.

Talk with the HES team and they will quickly flag up a recognition of the value of creating pollinator corridors and stepping stones across Scotland’s landscape. They link that desire equally to linear features such as the natural corridor created by the Tweed where the likes of Dryburgh and Melrose Abbeys feature, and this is an area which supports the Buglife Pollinators along the Tweed project. It’s a mix of identifying a range of opportunities which shows neatly their flexible yet determined outlook.

Not all interventions to help pollinators need to be high profile or involve significant new plantings. Often not doing very much in green space can be a huge help. Where nature is left to its own devices the results are often pleasingly satisfactory.

Staff at Dryburgh Abbey wanted to recreate an early 19th Century landscape and six years on the fantastic flowering meadows they have created are set to inspire other HES sites.

Mark Gillie, head gardener at Dryburgh is delighted with the progress that’s been made: “It was 2017 when we first started to move away from the manicured lawns you usually associate with the places like Dryburgh Abbey.  We now have many natural growing areas, and in around a third of them we have introduced wildflower seeds. Just within one small patch you can see daisies, yellow rattle, yarrow, orchids and many more – and you can also see the insects which need them.”

Of course there is a need to be sensitive in any approaches of this kind given the importance of the sites involved. As Sarah Franklin, Landscape Manager at HES explains: “We will be taking this approach forward, although some sites have sensitive archaeology and that can make life difficult for establishing wildflower meadows.. We can’t just lift the turf and scatter seeds around many historic buildings, but we will be looking to recreate what we have here at Dryburgh on sites where we can.”

A key strength in the HES approach is their desire to work in partnership with others. To this end they have recently been devoting considerable effort into a natural corridor created by the Tweed, work which blends neatly with the Buglife Pollinators along the Tweed (PATT) strategy.  

HES and Buglife Scotland met recently to discuss their partnership and visited both Melrose and Dryburgh Abbey. There is growing excitement about opportunities for the two groups to work together in habitat creation and meadow management skills such as scything training for staff and volunteers too. 

Over in the west, at Iona Abbey, a simple change in mowing regime has been really successful too, with the site buzzing and lots of visitors complimenting the staff on how much better it looks compared to when strict mowing was the order of the day. 

Of course, Scotland’s vital historic sites are often rigidly protected from development, which in turn can make them special havens for biodiversity as the habitats and species benefit from that greater level of protection.

NatureScot and Historic Environment Scotland can dictate outcomes for nature by coming together in sharing good practice. This is already happening successfully in our collaboration on the Dynamic Coast project. 

Now the goal is to replicate this team work in enhancing opportunities for pollinators. By pooling information on practices such as meadow management, removing arisings, following planting and flowering regimes which best suit pollinator life-cycles, and cutting carbon footprints there is clearly a shared agenda. 

We have the knowledge, we have the desire … watch this space.

Further reading

Find out more about the work at Dryburgh Abbey in this BBC article.

Sow Farr, sow good

Meadows don’t stand still. I was reminded of this when chatting to Paul Castle of Highland Council recently. We got to talking about Farr Glebe in Bettyhill, and he was quick to let me know about the fantastic work being carried out by North Sutherland Wildlife Group.  Under the catchy title ‘Sow Farr, Sow Good’ they have been using the meadow to great effect for pollinators … and people.

The project is set to run for at least the next couple of years. Hopefully it will further increase the flowering both within the meadow, and the area’s surrounding gardens.

In June of this year NatureScot funding, through the Volunteering Matters Action Earth initiative, helped with a planting event at Farr Glebe. As Susan Kirkup was delighted to note, “Lots of lovely healthy plants grew from our wildflower seed collected last year, so we had a planting pop-up event at the Farr Glebe Bumblebee Meadow. The weather was perfect ,and we had a good turn-out of people to help plant the barer areas of the meadow. Over 150 plants were put in – thereafter it was fingers crossed for good growing weather and that a decent number of plants reach maturity.”

Seed collecting had taken place the previous autumn and was well planned. An open invitation was extended to the local community, and the offer was made that people could grow some of the seed into plants in their own garden as well as replanting back at the Glebe. That was a fantastic way to extend the reach of the project.

Of course, this is Scotland and as we all know the weather can occasionally be, shall we say, challenging. Thus the seed collecting invitation reminded interested parties that the seed would need to be ripe and the weather dry. Therefore, the date of the collection was inevitably likely to be at short notice and dependent on a fair-weather forecast. 

The project is part of a programme to help further diversify the popular meadow at the Farr Glebe Bumblebee Reserve in Bettyhill. The reserve is an important area for many bumblebees including, the nationally rare great yellow bumblebee (Bombus distinguendus), one of the Species on the Edge targets.

One intention is that seed will help to improve parts of meadow which are currently  less diverse. A key ally in this quest is yellow rattle (Rhinanthus minor), encouragingly also known as ‘the meadow maker’ and which only grows in association with various grasses. 

Highlife Countryside Ranger Paul Castle is clearly delighted to work with the North Sutherland Wildlife Group. He makes no bones about their fantastic support for Farr Glebe and makes every effort to be on hand to explain the importance of the reserve and the work to help the bumblebees of north Sutherland. The ace up his sleeve is that he can suggest visitors might glimpse one of the rarest bumblebees in the UK, the Great Yellow.

Paul is full of praise for the work the wildlife group volunteers carry out.  “After the seed gathering exercise there was a fantastic team effort to propagate things and enhance Farr Glebe. Amongst the seeds under Susan’s care were greater knapweed, field scabious, tufted vetch, burnet saxifrage and black medic. Thanks to everyone’s hard work we quickly had 90 greater knapweed and 50 field scabious for planting out at the Glebe bumblebee meadow.”

Farr Glebe is an important pollinator site in Sutherland and the team behind it are keen to do more. In an ideal world they would look to extend the site, but for now working with the local community to continually improve the site and spreading the word is a fine achievement.

Further reading:

Find out more about the work of the North Sutherland Wildlife Group. 

Revisit our 2020 blog about Farr Glebe

All images courtesy and copyright of Stephen and Susan Kirkup

Adaptation prodigies

By Athayde Tonhasca

Most flowering plants depend on animals – typically insects – for their pollination and sexual reproduction, and pollinators are compensated for their services with floral resources such as pollen, nectar, oils and fragrances. These products are metabolically expensive, so plants use all sorts of devices to minimise consumption without risking their chances of fertilisation. They may lock their pollen inside anthers, so that only specialised bees can get to it by buzz-pollination; other species produce pollen or nectar that are toxic or hard to digest except by a select group of pollinators. Some plants, orchids in particular, offer no rewards of any kind and resort to sophisticated trickery such as sexual deception, which is the use of physical or chemical decoys to attract insects looking for a mating partner, or food deception, which is falsely advertising pollen or nectar with colour, scents, flower shape, and pollen-like structures. From 30 to 40% of the 28,000 or so known orchid species are deceitful: there’s a lot of cheating going on in the plant world. 

Bees and flies are the typical victims of these subterfuges, but Disa forficaria, a rare and endangered South African orchid, has an unusual target: a beetle. The flower releases a scent irresistible to male longhorn beetles (Chorothyse hessei), so much so that the passionate male tries to copulate with the flower, pollinating it in the process (Cohen et al., 2021: scroll down the paper’s page to watch the beetle in flagrante delicto).

L: Parts of a D. forficaria flower: petal (p), anther (a), dorsal sepal (ds), viscidium (v), stigma (s), labellum or lip (l) and lateral sepal (ls). R: C. hessei biting the petals and extending the tip of its abdomen into the labellum cleft. Scale bars = 5 mm. Images by C. Cohen, W.R. Liltved & S.D. Johnson © Cohen et al., 2021.

Resorting to sexual deception is especially important for D. forficaria because the species is quite rare; it relies on male beetles finding its flowers widely and thinly scattered in the landscape, while pseudocopulation assures the collection and transfer of pollen to another plant. A generalist pollinator would be less effective, which could spell disaster for the fragile orchid population.  

L: C. hessei with pollinaria of D. forficaria attached to it; R: A flower with pollen (arrow) adhering to the stigma immediately after a visit by C. hessei. Scale bars = 5 mm. Images by C. Cohen, W.R. Liltved & S.D. Johnson © Cohen et al., 2021.

While D. forficaria attracts its pollinators with fraudulent promises of sex, D. nivea resorts to impersonation. This rare orchid from South Africa’s Drakensberg region grows cheek by jowl with the unrelated Zaluzianskya microsiphon (family Scrophulariaceae), whose nectar-rich flowers are avidly visited and pollinated by the fly Prosoeca ganglbaueri. Plant and pollinator seem to have been made for each other, as Z. microsiphon flowers have long corollas and their fly visitor has a very long proboscis. 

P. ganglbaueri visiting the flowers of Z. microsiphon © Anderson et al., 2005.

But it so happens that flowers of both plant species look alike – or at least are similar enough for insects, whose eyes aren’t great for sharp image resolution. So, mistakes are inevitable: a P. ganglbaueri fly now and then sticks its proboscis inside an orchid flower, which has no nectar to offer. The fly goes way, often with a blob of pollen attached to its proboscis. If the fly gets it wrong again, it’s a score for the orchid: it gets pollinated (Anderson et al., 2005).  

A Z. microsiphon flower (bar = 20 mm) (L), and a D. nivea flower (bar = 13 mm) © Anderson et al., 2005.

Floral mimicry has been known for a long time: Christian Konrad Sprengel (1750-1816) spoke of Scheinsaftblumen (sham nectar flowers), and suggested their purpose was to deceive visitors. Many naturalists doubted that insects could be repeatedly fooled by such trickery. Darwin wrote that anyone who believes in ‘so gigantic an imposture’ must ‘rank the sense or instinctive knowledge of many kinds of insects, even bees, very low in the scale’. But insects do fall for it, and the chicanery seems to be working quite well for the orchid: its pollination rate in the Drakensberg region is linked to the abundance of Z. microsiphon.

A P. ganglbaueri posed next to a D. nivea flower. The fly is carrying two pollinaria of D. nivea at the base of its proboscis. Bar = 8 mm © Anderson et al., 2005. 

While D. nivea fools a fly, a related species from the Western Cape Province, D. ferruginea, targets a butterfly – the table mountain beauty (Aeropetes tulbaghia). This orchid produces no nectar, so it relies on the butterfly mistaking its red flowers for the blooms produced by nectar-rich Tritoniopsis triticea (family Iridaceae). But the orchid’s skulduggery goes further: it grows as an orange-flowered form in Langeberg, a mountain range in the Western Cape. The butterfly would be less easily fooled by red flowers, but here the orchid mimics the yellow-flowered and nectar-producing red-hot poker (Kniphofia uvaria, family Asphodelaceae) (Johnson, 1994).

The orchid D. ferruginea (L) and the iris T. triticea © Andrew massyn, Wikimedia Commons.

In South Africa, the table mountain beauty is hoodwinked by nectar-less red or yellow D. ferruginea orchids. Art by P. Cramer & C. Stoll, Wikimedia Commons.

Other Disa species play similar ruses by using some other elaborate adaptation – colour, scent or shape – to attract pollinators. But not all Disa orchids are swindlers: some species do offer nectar rewards to moths and other insects. And two species, D. chrysostachya and D.satyriopsis, have an unusual association with the malachite sunbird (Nectarinia famosa). These orchids produce small flowers tightly packed along a spike-shaped inflorescence. To get their nectar, the sunbird perches on the inflorescence; when it takes off, its feet will be covered with sticky pollen that, with luck, will be deposited on the receptive flowers of another orchid (Johnson & Brown, 2004).

A D. chrysostachya and its pollinator, the malachite sunbird © Alandmanson, and Steve Garvie, respectively. Wikimedia Commons.

There are over 180 Disa species, with about 120 of them in South Africa’s Cape region. Most are pollinated by a single group of insects, which could be butterflies, moths, long-tongued flies, carpenter bees, mason bees, wasps, and a bird; some species self-pollinate. Johnson et al. (1998) identified 19 specialized pollination systems for 27 Disa species: who knows how many more are yet to be discovered.

These unassuming orchids have evolved a remarkable range of features involving sexual deception, food deception, shapes, colours, and scents – all adaptations to reproduce and survive. We may not see such an array of strategies from the plants we are familiar with, but they certainly will have gone through some adaptive fine-tuning with their own flower visitors. Plants and their pollinators offer us some of the best examples of the power of natural selection.

Natural selection in action: each of the 18 or so species of Darwin finches in the Galapagos have beak sizes and shapes fitted for different types of food: seeds, insects, cactus flowers and fruits, or even bird blood. Art by John Gould (1804- 1881), Wikimedia Commons.