Blood, toil, tears and sweat

By Athayde Tonhasca

The Paraguayan War (1864-1870), waged by Paraguay against Argentina, Brazil and Uruguay, has a special place in mankind’s history of cruelty, carnage and devastation. Among the many horrors witnessed by combatants and observers, the episode described by Lieutenant Alfredo d’Escragnolle Taunay is particularly odd and gruesome: “Another plague persecuted them [horses, mules and asses] relentlessly, and this singular one had disastrous effects. It came from some extremely beautiful butterflies, the so-called 88, as they appear to have that number written on the outside of their brindled wings with whimsical black-and-white drawings. However, one cannot imagine the actions of those gentle Lepidoptera, in appearance quite innocent, but in fact extremely pernicious, in all that part of Paraguay. They would huddle together in the corners of the eyes and in the nostrils of the animals, seeking any bodily moisture and soon causing such irritation at the spots where they stubbornly landed, and it did not take long to produce abundant discharge, at first of mucous and soon after copious pus! A horror! What despair from our unfortunate mounts struggling to defend themselves from the immense, flagellating legions of tiny enemies, ever more numerous and ferocious! What continuous and tiresome weaving! Unable to graze, they grew thin under our eyes and soon were completely blinded! Once on the ground, surrounded by thousands of assailants, each eye socket became a hideous and disgusting source of purulent rivers, which attracted even more the terrible butterflies. We would have surely lost all our beasts of burden and mounts, if adequate measures had not been taken, by providing them with a headband of maize straw cut into fine threads, which served as a shield to the eyes without obstructing their view.” (Taunay, 1874. Recordações de guerra e de viagem).

Caught in the maelstrom: during the Paraguayan war, horses would succumb to wounds, hunger, exhaustion, cold, and butterflies. Art by Pedro Américo (1843-1905), Wikimedia Commons.

This butterfly worthy of a Stephen King novel is the Cramer’s eighty-eight (Diaethria candrena), which ranges from eastern Paraguay to southwestern Brazil, northern Argentina, and Uruguay. Adults are often seen in orchards, as they feed on rotting fruit. They also concentrate at the edge of ponds and puddles, on spots covered by ash after fires, and in bare soil soaked with livestock urine. This gathering behaviour was known by Tupi-Guarani speakers as panapaná, ‘a gang of butterflies’. For Anglophones, these butterflies are ‘mud-puddling’.

Butterflies mud-puddle supposedly – data are scarce – to collect salts, especially sodium. This chemical element is one of the most abundant in the Earth’s crust but occurs in minute quantities in plants because they don’t need much of it. That’s a problem for plant feeders, who require sodium in concentrations 100 to 1,000 higher than what they get in their food. Herbivores rely on their metabolism to accumulate sodium, and also on any alternative sources such as mineral licks, which are natural deposits of salts and other minerals: they are found in places such as exposed, muddy areas high in clay and organic matter. Faeces and dead bodies will do as well.

Most mud-puddling butterflies are males, so researchers have suggested – again, data are lacking – that nuptial gifts are behind this behaviour. The sodium gathered by males would be passed to females during copulation and then to the offspring, helping them to cope with a sodium-poor diet. But as females of some species mud-puddle as well, there must be more to the story.

Butterflies and other insects visit mineral licks to get their sodium fix, but these deposits may not be enough for their needs. The bodily secretion of some animals – sweat – is an attractive alternative for a bold insect willing to risk being squashed by an angry host in exchange for a lick of salt. Several species in the second largest family of bees, the Halictidae, are known as sweat bees because they use perspiring people as their salt licks. These bees are harmless, but can be quite annoying with their persistent hovering and tickling

Besides sweat, tears are an excellent source of salts, a fact enthusiastically exploited by the Cramer’s eighty-eight in Paraguay to the chagrin of poor horses and their minders. And a surprisingly large number of butterflies, bees, flies and other insects drink tears. In addition to horses, these insects take their salty beverage from cattle, sheep, pigs, water buffaloes, antelopes and elephants; birds, crocodiles and turtles are also suitable. In Burma, India, Sri Lanka and Thailand (and probably other countries too), human beings are also involuntary tear donors to at least six species of moths. Besides the ick factor, tear-seeking insects are to be avoided because of the risk of transmission of eye diseases such as the trachoma virus and ‘pink-eye’ (conjunctivitis) in human beings (Bänziger & Büttiker, 1969).

A Lobocraspis griseifusa moth sucking tears © Bänziger & Büttiker, 1969.

As lachryphagy – from the Latin lacrima (tear) and the Greek phagos (eating, feeding) – is fairly common, Bänziger et al., 1992 proposed that there’s more to it than just sodium taking. Insects may be after amino acids and proteins, which occur in tears in fairly high concentrations. The researchers noted that tear-dinking bees rarely visit flowers or carry pollen, which suggest they may be getting all or most protein they need to raise their young from tears. 

Alas, sweat and tears may not satisfy the mineral/protein needs of some insects. 

Many moths and butterflies feed on extra-floral nectar, sap, or decaying fruit as the Cramer’s eighty-eight does. But some moths in the subfamily Calpinae (family Erebidae) don’t have to sit around waiting for a fruit to break open: they use their stout proboscis, which is armed with hooks and barbs, to pierce the skin of a fruit to feed on its flesh and juices. Some species in the genus Calyptra in Southeast Asia found another use for their tough proboscis: to feed on the fluids exuded by cuts, sores, scratches, scabs, and other open wounds of animals. 

Distal region of the proboscis of Gonodonta bidens, a fruit-piercing moth. Lgl are legulae (rasping spines), and th are tearing hooks © Zenker et al., 2010. Journal of Insect Science 11:42

It takes a small step to go from exploring a host’s skin for an open wound to piercing it to get access to the richest bodily fluid of all – blood. Some Calyptra species have developed the ability to puncture the skin of cattle, pigs, mules, deer, antelopes, water buffaloes, elephants and rhinoceros. If these moths can pierce rhinoceros skin, they would have no difficulties with a hairless, thin-skinned primate: at least five Calyptra moths are known to feed on humans. Predictably, they are known as vampire moths.

If you want to place blood-sipping moths in the list of bizarre creatures from faraway tropical countries, think again. The vampire moth Calyptra thalictri, originally from Asia and Eastern Russia, has slowly expanded its range to northern Europe, being observed in Finland and Sweden. Watch C. thalictri having a vampirism moment, but nobody should lose sleep over it: human blood feeding by moths is harmless and extremely rare. Calyptra spp. diet comprises mostly soft-skin fruits (raspberry is a favourite), which they puncture to reach the sugar-rich juices.

Calyptra thalictri © Ilia Ustyantsev, Wikimedia Commons.

Approximately 14,000 insect species are hematophagous, that is, they feed on animal blood. Most of them are obligatory hematophagous: they need blood as a source of nutrients and cannot survive on any other food. Some butterflies and moths on the other hand are facultative hematophagous: blood is not vital for them, but increases their chances of survival. In the case of vampire moths, only males feed on blood. So just like for mud-puddling butterflies, male moths apparently are after sodium as a nuptial gift, which they would pass to females during mating.

An obligatory hematophagous specimen. From Archive of Dracula (1931), Wikimedia Commons.

The sodium-gathering hypothesis suggests that mud-puddling, sweat-licking, tear-drinking and blood-sucking are related behaviours. It is also notable that one morphological adaptation, i.e., a sturdy and barbed proboscis, allowed some moths to evolve from nectar-sipping to fruit- and skin-stabbing. Calpinae moths offer another example of insects’ spectacular capacity to adapt and make use of whatever nature has to offer.  

Incidentally, in case you are pondering whether lieutenant Taunay – later a Viscount – exaggerated or made up his butterfly story (porkies are not unheard of in war memoirs), a similar albeit less dramatic episode was witnessed about half a century later in the vicinity of Iguazu Falls, not too far from the Paraguayan killing fields. ‘Volunteer’ horses had their eyes mobbed at night by no less than eleven species of moths (Shannon, 1928. Science 68: 461-462).

So, are equines at risk from Lepidoptera attacks in central South America? They are not. All the countries involved changed beyond recognition since the war: much of their natural habitats have been converted to soybean fields, pasture and logging wasteland. Numbers of butterflies, moths and just about any other wild animal have plunged, some to the point of near extinction. In these inhospitable environments, the Cramer’s eighty-eight could never reach the Biblical numbers of the past, to the relief of local livestock. You may think of it as silver lining of sorts.

An eighty-eight butterfly, no longer pestering horses. In the background, the Iguazu Falls © Leoadec, Wikimedia Commons.

Saving Scotland’s species-rich grasslands

Apithanny Bourne is our guest blogger today. Currently in her third year of a NERC funded Environment Doctoral Training Partnership at Edinburgh University, in conjunction with Scotland’s Rural College, Apithanny is looking at Scotland’s species-rich grasslands and assessing their quality for pollinators using remote sensing. Monitoring floral habitats is a subject well known to Apithanny in her capacity as the Chair of the East Scotland Branch of Butterfly Conservation.

Species-rich grasslands are captivatingly beautiful and rich in biodiversity – there is nothing quite like walking through a buzzing, blooming meadow in June. These special places support a vast array of wildlife and provide essential ecosystem services during a time of climate chaos, as rich grassland soils are one of the most effective carbon stores of any UK habitat. So why have we lost a devastating 98% of our lowland meadows in less than a century? Throughout my PhD, I aim to research Scotland’s remaining fragments of species-rich grassland and the fascinating butterflies relying on them for survival. 

Species-rich grassland on west Coast of Scotland, brimming with Harebell and Eyebrights.

“The British countryside has changed dramatically since the end of the Second World War. Within a single generation, hay meadows that were once an essential part of everyday life, were rapidly replaced by the monoculture pastures now dominating much of our landscape. Many native wildflower species thrive on nutrient-poor soils and alongside sympathetic farming practices, meaning they cannot tolerate today’s intensive use of fertilisers and herbicides. Coupled with the common practice of reseeding grassland with a vigorous fodder crop of Perennial Ryegrass– productivity in modern agriculture has supplanted the traditional hay meadow. 

“This loss of floral habitat from the landscape is undoubtedly one of the driving factors behind pollinator decline in the United Kingdom. A recent report by Butterfly Conservation found 80% of our native butterfly species are in decline, whilst data from the Bumblebee Conservation Trust indicates worrying downward trends for some of our most common and much-loved bumblebee species. Insects and plants typically receive less attention and funding when compared with better-known species and habitats – but these alarming statistics should be a wake-up call. Monitoring the quality of our remaining meadows and recording the pollinators they support is essential for ecosystem health, food security and human wellbeing. Unfortunately, traditional survey techniques are expensive and often require an in-depth knowledge of species identification, accumulated over many years. A lack of expertise in species identification is often a limiting factor when it comes to monitoring insect species and grassland types.

Comparison of (a) Ryegrass “improved” pasture and (b) a restored hay meadow blooming with Yellow Rattle

“I hope to tackle some of these issues during my PhD, which is funded by Scotland’s Rural College (SRUC) and Edinburgh University and aims to promote multidisciplinary research within the School of Geosciences. Whilst performing more traditional botanical surveys and pollinator counts, I have also been collecting high resolution imagery using drones and cameras. By flying a drone above transects in floral habitats, I am able to collect hundreds of images that can be stitched together into a 3D model, in which individual flowers are clearly discernible.

“I aim to use this image database with a technique called object-based classification, to remotely assess the type of grassland habitat and its quality for pollinators. This will work using computer software trained to identify indicator species and hopefully calculate other useful metrics, such as the abundance and percentage cover of flowers. By extracting data from images of floral habitat, I will determine which factors best predict pollinator abundance and richness on the ground. The use of technology in conservation offers great potential as a user-friendly, cost effective and rapid approach to assessment. It could offer efficient long-term monitoring of both protected sites and results-based agri-environment schemes – providing advice on habitat management and allowing quick intervention where sites begin to decline in quality.

Mavic pro drone out in the field.

“For the past two summers, I have been busy collecting data and imagery from some wonderful sites across the Scottish Borders, Midlothian and Fife. The scarcity of meadows has expanded my study area and whilst I absolutely love my field work, I am struck by how small and fragmented these remaining pockets of habitat really are and how difficult it must be for species to move between them. My sites range from degraded hay meadows to botanically rich Sites of Special Scientific Interest (SSSIs), allowing me to record how the pollinator communities change along a gradient of grassland quality. At more diverse sites, I have enjoyed the company of shimmering Dark Green Fritillaries, fairy-like Northern Brown Argus butterflies and bewitching wild plants like the Greater Butterfly Orchid. As you might expect, overgrazed or ‘improved’ grasslands hosted mainly generalist species and in very low abundance. 

A selection of some wonderful species found in rich grasslands.

“Writing this blog post for Scottish Pollinators could not be more apt, as I truly fell in love with species-rich grasslands during a botany internship at NatureScot. Meadows are an important part of our natural and cultural heritage and I firmly believe that everybody should be able to enjoy them – something that keeps me motivated as I begin to analyse my data and prepare my work for publication. We must all work hard to protect and restore ancient pastures, whilst championing the creation of new floral habitat. Let’s hope that technology will help us to achieve this, through locating, assessing and mapping remaining grasslands quicker than ever before.”

Restored meadow with Greater Butterfly Orchid

All photos courtesy and copyright of Apithanny Bourne

Pollinators in Estonia

Eneli Viik, who works for the Centre of Estonian Rural Research and Knowledge (METK) is our guest blogger today. She develops and promotes activities aimed at preserving the biodiversity of agricultural landscapes and has made a major contribution to the biodiversity monitoring of agri-environmental measures. Eneli is a valued speaker at international and domestic events and has prepared a publication introducing Estonian bumblebees.

Adult hoverflies are important pollinators while larvae contribute to natural pest control. There is very little data about hoverflies biology and abundance in Estonia and only a few experts. (c) Arne Ader.

“The most important natural pollinators in Estonia are bees (bumblebees and solitary bees) but butterflies, hawkmoths and hoverflies also contribute to pollination. How are they doing in Estonia?

“There are 276 species of natural bees known in Estonia. According to the fifth IUCN evaluation of species vulnerability 5% of them are extinct in the region, 3% critically endangered, 4% endangered, 12% vulnerable, 6% near threatened, 64% least concern, 1% data deficient and 5% not evaluated.

Bombus veteranus has decreasing trends in Estonia and belongs to IUCN category „near threatened“. Bumblebees have got quite a lot of attention through monitoring, studies and projects in Estonia.
(c) Urmas Tartes. 

“More specifically, the list of bumblebees contains 21 species of true bumblebees and 8 species of cuckoo bumblebees. According to IUCN criteria 16 species of true bumblebees were evaluated in 2020 to be of least concern, 2 near threatened, 1 vulnerable, 1 endangered and 1 extinct in the region (Bombus laesus). Out of the 8 cuckoo bumblebee species 6 are least concern, 1 is near threatened and 1 was not evaluated.

“Bumblebees have been monitored in the context of national environmental monitoring since 1996, and since 2020 with updated methodology across more sites. Since 2006, bumblebees have been monitored also in connection with Rural Development Plan agri-environment schemes with evaluation focusing on agricultural landscapes. This work has been coordinated by the Centre of Estonian Rural Research and Knowledge. Bumblebees have also been studied under different national and EU funded studies and projects. 

“True bumblebees have received more attention than cuckoo bumblebees. Based on available data the status of bumblebees generally is quite stable. On the other hand, some species (including Bombus veteranus and two long-tongued species B. distinguendus and B. hortorum) have decreasing trends and have become more vulnerable.

(247 solitary bee species have been found in Estonia but there are only a few experts and no monitoring. 
(c) Margit Mõttus.

“At the time of fifth IUCN evaluation in Estonia there was a shortage of data about solitary bees. To improve the knowledge, a revision of Estonian bee fauna was carried out in 2018—2020. Based on the results of 247 solitary bee species found in Estonia, it was concluded that 12 species are endangered, 6 critically endangered and 13 extinct in the region. The endangered and critically endangered species are very rare local species with very few findings recently. In general, the knowledge about solitary bees is still scarce: there are only a few experts available and no monitoring currently.

 Inachis io is a common species in Estonia. Butterflies are quite well known and noticed in Estonia.
(c) Arne Ader.

“103 butterfly species out of Estonia’s known 116 species were evaluated in 2017—2018 according to IUCN criteria: 87 butterfly species are least concern, 3 near threatened, 2 vulnerable, 7 endangered, 1 critically endangered and 3 extinct in the region. Species in the endangered and extinct categories are there due to climate changes and/or because they are associated with habitats like dry alvar meadows and heaths — areas which in Estonia have decreased. Valuable input for the evaluation was received from Estonian butterfly distribution mapping carried out in 2016—2017 which included more than 1200 sites across Estonia. According to butterflies communities monitoring in the frame of national environmental monitoring programme the abundance trend in 2004—2019 was even slightly positive. Since 2020 monitoring methodology was changed and more sites are monitored annually.

“In case of hawkmoths 11 species from 17 were evaluated according to IUCN criteria (6 are rare migratory species). All evaluated species were of least concern. Actually, only 4 species of hawkmoths can be considered as considerable pollinators in Estonia and according to the monitoring of moths communities in the frame of national environmental monitoring programme since 2003 these species trends are stable.

“There are 221 species of hoverflies known in Estonia but there is very little data about their biology and abundance. Therefore, it was not possible to evaluate the IUCN vulnerability status of most of the species and the trends are currently not known. There are only a few experts on hoverflies and no monitoring in Estonia.

“At the moment there is no strategic document for natural pollinators in Estonia, but in the frame of LIFE-IP project ForEst&FarmLand national pollinators’ action plan will be worked out by the end of 2024.

“So far, the actions to favour pollinators are mainly related to agricultural land where different measures can be applied in the sphere of EU common agricultural policy. 

“A list of some examples of measures, requirements and restrictions up to 2022 would include the following: 

  • obligation to grow leguminous crops, 
  • leaving 2—5 m wide grassland field margins, 
  • limitations to the use of glyphosates or other pesticides, 
  • compulsory trainings to raise awareness, 
  • supporting organic farming, 
  • supporting the management of semi-natural habitats, 
  • including biodiversity elements in horticulture, 
  • maintaining landscape elements, 
  • maintaining certain share of permanent grasslands. 

“There is also a measure ‘establishing foraging areas for bees’ the main target of which is honeybees. So, there are actually no measures specifically targeted at natural pollinators. Pollinators are indirectly favoured also through the legislation related to pesticides.

“There are also some other small-scale activities outside agricultural land. For example, in recent years, the city of Tartu has started activities promoting urban biodiversity: flower-meadows have been created in the city-centre and spring-flower patches in shady parks to raise public awareness about the importance of species diversity. 

“An important factor in maintaining pollinators is also citizen science and interest in pollinators. There are some materials about bumblebees and butterflies of Estonia but none for solitary bees, hawkmoths and hoverflies. A citizen science project about bumblebees was carried out in 2014 to raise citizens´ awareness and as a result of the project a Facebook group “Our bumblebees” was created (later renamed for “Our bumblebees and solitary bees”). In the group people can share photos, get support in assigning the species and share other relevant information (more than 1200 members). 

“Another similar Facebook group is for “Butterflies and moths of Estonia” (more than 3300 members). The Estonian Fund for Nature focused in 2018 on their voluntary actions related to semi-natural habitats restoration as well as on bumblebees and along with giving some lectures made bumblebees movies. 

“There are some citizen science platforms where nature observations, including pollinator observations, can be entered. Observations of protected species are cross-checked by an expert and entered into the Estonian Nature Information System. Popular science articles also help to raise public awareness about natural pollinators and give suggestions how to favour these useful insects – for example, suggestion not to mow the lawn so often and let the flowers bloom but also growing food plants specifically for pollinators in their garden.

“During 2020—2021 the Centre of Estonian Rural Research and Knowledge participated in a project financed by the Nordic Council of Ministers. Countries participating were Norway (the lead partner), Sweden, Denmark, Finland, Estonia and this cooperation was called the North-European bumblebee network. The project included different awareness raising activities: producing online and hand-out materials, movies and webinars.

“In order to maintain Estonian pollinators’ populations, it is necessary to consider their species-wise characteristics. Thus, diverse landscapes are needed to ensure many different habitats with nesting sites but also diverse and abundant food resources throughout the activity season.”

Thanks to Eneli for a fantastic insight to what’s happening regarding pollinators in Estonia. We will keep a close eye on how things develop and wish our counterparts in Estonia all the best with their projects.

Dubious helpers

By Athayde Tonhasca

Eikyu Matsuyama, an apple grower from Aomori (the northernmost prefecture on Japan’s main island), noticed mason bees building nests inside holes in utility poles and wooden walls near his orchard. As this species of bee (Osmia cornifrons) was a keen visitor of apple flowers, Mr Matsuyama pondered whether he could attract more bees to his orchard by supplying them with pieces of reed as extra nesting sites. This was the 1930s, when apple pollination in Japan was mostly done by hand – a labour-intensive, costly operation. Sometimes the military was recruited to help pollinate apple flowers during the two-week bloom period. Aomori was – and still is – the leading apple-producing region in Japan, accounting for nearly half of the country’s harvest. So any extra help from bees would be much appreciated by the growers.

An apple blossom in the Aomori prefecture with Mount Iwaki in the background © 岩浪陸, Wikimedia Commons.

Mr. Matsuyama’s experiment was a huge success; soon the numbers of mame-ko bachi (the bee’s Japanese name) expanded dramatically, with a corresponding improvement in apple production. Other growers quickly followed suit, and Mr Matsuyama went on to lecture about mason bees at several Japanese universities (Mader et al., 2010). 

In the 1960s, apple growers in the Aomori Prefecture began to use the European honey bee (Apis mellifera) as an alternative pollinator, while researchers improved propagation and management methods for the mame-ko bachi, named the Japanese hornfaced bee in English-speaking countries. Nowadays Aomori growers of apple, pears, peaches and plums are likely to use commercially available Japanese hornfaced bees instead of honey bees because the former is considerably more efficient. It visits about 15 flowers per minute (4050/day) and carries ~267,000 grains of pollen on its scopa (pollen-carrying bristles), while the honey bee visits about 6 flowers per minute (720/day) and transports ~100,000 grains of pollen. Equally important, the Japanese hornfaced bee, like other species in the group, is a bit sloppy in transferring pollen to her nest; about 10% of it remains on her body (Matsumoto et al., 2009). This residual pollen, viable for up to 12 days, has a good chance of ending up on a receptive apple flower and pollinating it.

A Japanese hornfaced bee leaving its nest © Beatriz Moisset, Wikimedia Commons.

The Aomori Prefecture achievements with the Japanese hornfaced bee didn’t go unnoticed. In the 1960s, the American Agricultural Research Service (Department of Agriculture) introduced this species to America to improve pollination of fruit crops such as apple and blueberry. Since then, the Japanese hornfaced bee has spread through the eastern and mid-west United States. And in 2002, another Asian mason bee was found doing its bit for pollination in America: the taurus mason bee (Osmia taurus). Nobody knows how or when this species entered the country: it probably was introduced accidentally at the time of Japanese hornfaced bee importation. These two species look alike superficially, so an unintentional introduction is plausible.

Female Japanese hornfaced bee (L) © Chelsey Ritner, and taurus mason bee © Chelsey Ritner, Exotic Bee ID.

Bees are overwhelmingly valued by the public, so the addition of two new species to the local fauna, even if inadvertently in one case, must be a good thing. Indeed, introduced bees may increase the local pollinating force. But these newcomers may also be harmful to native species and their habitat, most likely because of competition. This happens when two of more species need a common resource – food, water, a place to live – that is in short supply.

Assessing competition: Diet analyses from carbon (δ13C) and nitrogen (δ15N) isotopes indicate a considerable overlap of food taken by the invasive American mink (Neovison vison) and the native, critically endangered European mink (Mustela lutreola) in Spain; these results suggest a substantial competitive pressure imposed by the American mink on the European mink © García et al., 2020.

In the case of bees, the most likely problems from introduced species is competition for food (nectar and pollen) or nesting sites. These interlopers may cause less evident but no less serious problems; they may transmit novel pests and diseases to the native fauna, or they may alter the habitat by pollinating invasive plants and therefore helping them spread. These concerns are more than speculation; the European honey bee and the buff-tailed bumble bee (Bombus terrestris) are notorious for causing trouble in places where they have arrived. We know less about the other 80 or so bees introduced accidentally or deliberately outside their native range, but problems have been documented (e.g., Russo et al., 2020).

The yellow star-thistle (Centaurea solstitialis), a Mediterranean native, has been spreading through 41 of the 48 contiguous U.S. states thanks in part to pollination by the non-native European honey bee © J.smith, Wikimedia Commons.

The Japanese hornfaced bee and the taurus mason bee found America to be very much to their liking; their populations have increased dramatically since their arrival – reaching growth rates of three to five times per year, when conditions are favourable. This is not good news for the blue orchard bee (Osmia lignaria), a reliable orchard pollinator and a native species that has much in common with the intruders: they all emerge more or less at the same time, take pollen from similar plants, and have similar nesting habits. This overlapping of resources inevitably raises the possibility that the blue orchard bee would get the short end of the stick in these species interactions.  

A female blue orchard bee © Chelsey Ritner, Exotic Bee ID.

LeCroy et al. (2020) set out to assess just that. They examined trap catches of the two introduced bees, the blue orchard bee and other five native mason bees from four eastern American states from 2003 to 2017 (5,901 records). Their results: all native species declined from 76 to 91% since 2003, while the exotic species were doing just fine; populations of Japanese hornfaced bee were stable, while taurus mason bee numbers increased by 800% since 2003. This latecomer represented 22% of captures in the years 2003–2009, raising to over 43% of all captures from 2010 to 2017, making it the most common mason bee species in the region.

We don’t know the consequences of such dramatic population shifts. The two exotic species may take up the pollination work from the bees displaced by them, although a complete, seamless substitution is improbable: the dynamics between plants and pollinators are bound to become different, although we can’t say how. Native and alien bees may adapt and co-exist; in the worst case scenario, native species may become threatened. Many Americans would not be happy to watch their native bees pushed aside by intruders, no matter how benign or useful they may be. But there’s little they can do about it. Once alien species become established, it’s extremely difficult and expensive to get rid of them. 

Here in the UK, gardeners, allotment holders, schools and assorted nature lovers have shown increased interest in buying mason bees – and many suppliers, domestic and from abroad, are ready to oblige. But it’s impossible to tell whether these newcomers are healthy, or whether they will take food and shelter away from the local bee fauna. The case of the Japanese hornfaced bee and the taurus mason bee in the US is a cautionary tale about the uncertainties of species introductions: you are never sure how the story will end.

Pandora trying unsuccessfully to make amends for releasing humanity’s evils. Art by Frederick S. Church (1842–1924), Wikimedia Commons.

Plants and pollinators on the islands

If I were to stop a stranger in the street, and mention the phrase ‘Mid Ebudes’, most would understandably scurry off to consult Wikipedia. A very few might nod sagely, and acknowledge in a heart-beat that this was a reference to Vice County 103, a biological recording zone which likely dates back to the 1850s. In the latter camp you would find my former colleague Lynne Farrell, for the Mid Ebudes is ‘her patch’.

When I asked Lynne if she could provide a little insight into her dealings with pollinators in the course of her botanising she replied, as I knew she would, with a very accommodating ‘Yes’.  What follows is Lynne’s insight into the pollinators she has observed at close quarters whilst recording plants.

Lynne is one of our most noted botanists. She worked for both English Nature and Scottish Natural Heritage, is a Past President of the Botanical Society of Britain & Ireland, recorder for the Mid Ebudes since 1996. Her interest in botany and conservation remains as strong as ever, after a lengthy and distinguished career. 

“The three islands of Coll, Mull and Tiree are now collectively known for botanical purposes as Mid Ebudes,” explains Lynne. “We believe the name to be a corruption of the word Hebrides. Pliny the Elder about 77AD mentioned it in his Natural History stating that there are 30 Hebudes. Ptolemy used the name Ebudes, which may be of pre-Celtic origin. Old Norse is Suoreyjar meaning Southern Isles, and the Gaelic Innse Gall. Today we simply know them as the Outer, Mid and Inner Hebrides. 

“Since 1996 when I came to work in Scotland, I have been the botanical recorder for these islands, getting to know their natural history and the people.”

It’s a wonderful patch to cover.  As Lynne is quick to note, some of the species she has encountered are special and threatened. These include Oysterplant, Irish Lady’s Tresses, Eyebrights, Burnet moths, Great Yellow Bumblebee and Northern Colletes mining bee. They all feature in the Species on the Edge project, an ambitious programme which draws together nine species recovery projects in a partnership designed to achieve benefits for more than 37 vulnerable and threated species. 

“Even though research has been carried on some of these species for many years”, Lynne notes that “we still don’t know some of the answers to the relationship between the plants and the pollinators.” Nevertheless, I asked Lynne for a personal perception on the some of the species that have found themselves included in Species on the Edge

“Irish Lady’s Tresses orchid is an oceanic species which has a wide distribution in north America and, as its name suggests, is scattered around the west coast of Ireland particularly in Connemara, County Clare. The flowerheads resemble platted hair or tresses. In Britain it is largely confined to western Scotland in Argyll, Outer Hebrides, Colonsay and the Mid Ebudes. Perhaps surprisingly, given its status as a national rarity, it is quite mobile in its appearance in these areas. Often disappearing from traditional sites and regularly being found at new locations. It appears to have what you might call a ‘Goldilocks’ relationship with grazing: too little and the sward closes over its head, too much and it gets trampled and bitten off. On Coll, some of the key areas for it are managed by RSPB.  For many years we have being trying to find out what pollinates this orchid but so far very few insects have been observed visiting the tiny flowers and hardly any ripe seedpods have been produced. In North America this is no problem, so perhaps the answer lies there? Perhaps the insect which pollinates it further afield does not occur in Britain.

“Oysterplant occurs round the northern coasts of Britain and Northern Ireland where it grows in gravelly places, often at the top of beaches where it survives  ‘reshaping’ of the beach profile by storms. Orkney is its stronghold in Scotland, but it is found on Mull, Coll and Tiree also. It is an attractive, large, flowering plant with succulent leaves, supposedly tasting of oysters, and was eaten by people when it was more abundant around our coasts. Sheep and cattle still find it very edible and often graze it right down to the ground. It has very long roots, which hold it fast into the gravel, and the large, black seeds are scattered by the wind movements when they are ripe in autumn. They are carried along on the sea currents to new places where they may germinate several years later. Once again, there is little information about pollinators, but the pink and blue flowers are sufficiently open for bees to crawl into.

Great Yellow Bumblebee (c) and courtesy of John Bowler (RSPB)

“The Great Yellow Bumblebee is a real specialty of the Hebrides where it inhabits flower-rich sand-dunes and machair, where it occurs alongside a buzzing assortment of bees, including the striking agricola form of the Moss Carder and the ‘communal’ solitary bee, the  Colletes. The Great Yellow may once have occurred on Iona off the western tip of Mull, but in the mid Ebudes it is now confined to Tiree and Coll. Several research projects have been undertaken on the species over the last 20 years. It has declined on Coll, where it is now rare and very localised, although it remains widespread and locally frequent on Tiree. Recent findings indicate that the bee thrives in areas that have high densities of Kidney Vetch early in the season and Common Knapweed later in the season, with plenty of Red Clover in mid-summer. 

“All of the best areas for the species on Tiree benefit from agri-environment schemes that involve either a complete grazing break or a drop in stocking rates during the summer months to allow the machair flowers to bloom. It is a distinctive species, the queens are often larger in size than those of the ‘normal’ bumblebees, with a characteristic bright yellow body carrying a distinct black band on the thorax. You may be fortunate to see or hear it buzzing through the vegetation – calm sunny days in August are the best time to look, when the bees are at their highest density. 

“Burnet moths are also to be seen, with their distinctive black and red wings. But it is only on Mull where the rare Slender Scotch Burnet can be found. The similar Transparent Burnet is more widely scattered from the Mull of Kintyre, on Mull and Ulva, and northwards to Skye, Canna and Rum. However, it is the Six-spot Burnet which you are most likely to see during June, July and August.There are 10 species of Burnets recorded in Great Britain and Ireland and about 800 species worldwide. They live in colonies and the adults are active during the day, flying around from flower to flower mainly on warm, south-facing grassy slopes. On Mull active management is taking place to control invading Cotoneaster, which spreads quickly over the ground blanketing many of the low-growing herbaceous plants. Volunteers are needed , so if you fancy a working holiday on a Hebridean island, please get in touch with Butterfly Conservation Scotland.”

With a distinguished career as a botanist Lynne’s views are built on a solid bedrock of experience and dedication. You may not have heard of the Mid Ebudes, but chances are if you have an interest in conservation and botany you will know the name Lynne Farrell.

Further reading

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Great Yellow Bumblebee (c) and courtesy of John Bowler (RSPB)

Evolutionary dead ends

By Athayde Tonhasca

In 1842, the Darwin family – Charles, his wife Emma, and their two children William and Anne – moved to Down House in the village of Downe, England. The Darwin patriarch, who had travelled the world aboard H.M.S. Beagle (1831–1836), would spend the remaining 40 years of his life in quiet isolation at home because of ill-health. Darwin’s condition (whose origin still puzzles scholars) did not slow him down; he embarked on several projects such as monographs on coral reefs and barnacles, and of course overseeing the publication of On the Origin of Species. But Darwin spent most of his time working with plants, which are convenient study subjects for someone with a sedentary life-style. Assisted by gardeners and occasionally his children, Darwin observed and experimented with cabbage, foxglove, hibiscus, orchids, peas, tobacco, violets and many other species in his garden and glasshouse.

Darwin’s glasshouse at Down House, where he conducted many experiments © Tony Corsini, Wikimedia Commons.

Among various major contributions to botany (detailed by Barrett, 2010), Darwin documented the importance of cross-fertilisation (i.e., the transfer of pollen between different plants) for producing healthy offspring. Darwin, ever meticulous about supporting his theories with data, amassed eleven years of continuous observations to highlight the superiority of cross-fertilisation over self-fertilisation, i.e., the transfer of pollen within the same flower or between different flowers on the same plant. 

Methods of transferring pollen from the male anthers to the female stigma © Bartz/Stockmar/Ziyal – Insect Atlas, Wikimedia Commons.

Indeed, the great majority of flowering plants predominantly or exclusively outcross – that is, they mate with other individuals – even though they could easily self-fertilise because they are hermaphroditic (their flowers contain both male and female sexual organs). In fact, numerous flowers have mechanisms to avoid self-fertilisation. At best, many self-pollinated species (or ‘selfers’) exhibit mixed mating systems.

The bee orchid (Ophrys apifera). Despite its name, this orchid is mostly a selfer in northern Europe. In the Mediterranean, where this orchid is more abundant, its flowers are pollinated by bees © Bernard Dupont, Wikimedia Commons.

Self-pollination has some advantages: it helps to preserve desirable parental characteristics when a plant is well adapted to its environment. Because selfers do not depend on pollen carriers, they can colonise new habitats with a handful of individuals. Selfers do not have to spend energy on nectar, scents, or substantial quantities of pollen. Self-pollination is useful to farmers, as the genetic identity of a variety or cultivar is easily maintained, without requiring repeated selection of desirable features.

Comparing self-fertilised and crossed seedlings of common toadflax (Linaria vulgaris) in his garden prompted Darwin to investigate the effects of cross-fertilisation (Thompson, 2018) © Tony Atkin, Wikimedia Commons.

Self-pollination sounds like a convenient and rational lifestyle, but there are catches, and they are considerable. Selfers’ limited genetic variability makes them vulnerable to environmental changes; a hitherto well-adapted population can be driven to extinction if no individuals are adapted to novel conditions – and changes are inevitable, given enough time. Selfers are also particularly susceptible to inbreeding depression; if the population is homogeneous, genetic defects cannot be weeded out by genetic recombination.

Taking into consideration the long-term hazards of selfing, it seems paradoxical that 10 to 15% of all flowering plants from many taxonomic groups made the transition from outcrossing to full self-fertilisation. Darwin proposed an explanation for this puzzle: cross-pollinated species would turn to self-fertilisation when pollinators or potential mates become scarce. In other words, self-fertilisation assures survival when outcrossing becomes inviable. Darwin’s hypothesis, currently known as the ‘reproductive assurance hypothesis’, continues to be the most accepted explanation for the evolution of self-fertilisation.

Remarkably, researchers were able to quickly induce the transition from cross-pollination to self-pollination in the common large monkey flower (Erythranthe guttata, previously known as Mimulus guttatus) by preventing plants’ contact with pollinators (e.g., Busch et al., 2022). Monkey flowers kept in a glasshouse with no pollinators for five generations increased the production of selfing seeds and showed a reduction in the stigma to anther distance – this feature, known as herkogamy, is one of the indicators of ‘selfing syndrome’: the greater the distance between stigma and anther, the greater the likelihood of the stigma receiving external pollen, thus the lower the chance of self-pollination. After nine generations, plants experienced a significant reduction of genetic variability. Monkey flowers kept in another glasshouse with free access to the common eastern bumble bee (Bombus impatiens), one of the plant’s main pollinators, underwent none of these changes.

L: The common large monkey flower, a native to western North America. Its wide corolla and landing platform are convenient for its main pollinators, bumble bees © Rosser1954, Wikimedia Commons. R: Diagram of a large monkey flower with the upper corolla removed to show the reproductive structures © Bodbyl-Roels & Kelly, 2011.
A common eastern bumble bee; its absence induces selfing in large monkey flowers © U.S. Geological Survey Bee Inventory and Monitoring Lab.

What do these observations of the monkey flower tell us? For one thing, they are cautionary tales about the risk of losing pollinators. A variety of human disturbances such as agriculture intensification, loss of habitats and diseases have caused a decline of some insect populations, including pollinators. A scarcity of flower visitors may threaten pollination services directly, or induce some plants to adapt quickly and become self-pollinated. Adaptation sounds good, but selfers’ lower genetic diversity and reduced capacity to adjust to environmental vicissitudes make them vulnerable to extinction.

The renowned botanist and geneticist G. Ledyard Stebbins (1906-2000) suggested that selfing is an evolutionary dead end: it is advantageous in the short term but harmful in the long run. And because the transition from outcrossing to selfing is irreversible, according to Dollo’s Law (structures that are lost are unlikely to be regained in the same form in which they existed in their ancestors), self-fertilization ends up in irretrievable tears. And the monkey flower has shown that it all may happen before we notice it.  

Loss of pollinators could be the end of the line for plant species forced into self-pollination © Vaikoovery, Wikimedia Commons.

Finland forges ahead

There are 38 resident bumblebee species in Finland and they have been monitored since 2019. Some of these are of particular interest, being Lapland specialists, and in 2018 a popular book about bumblebees, the first ever to look at the species in Finland, cemented a growing public interest.

Bombus subterraneus (c) Mikko Kuussaari

This interest in bumblebees is perhaps indicative of a wider interest in pollinators generally in Finland. In 2022 this growing concern resulted in a national pollinator strategy.

Having acknowledged that bumblebee monitoring in Finland is in its infancy it is necessary to qualify that, with an acknowledgement that interest in bumblebees in Finland has a much longer history. As early as 1928 Olavi Hulkkonen, who worked as an assistant in Helsinki University’s botany department was responsible for one of the earliest publications on bumblebees. Sadly he died in his early thirties.  His work to some extent was continued by Karl Johannes Valle who was an entomologist and keen bumblebee watcher. He studied bumblebees until the late 1950s, mainly around the nation’s capital, Helsinki.  

With a population of 5.5m, almost exactly the same as Scotland, Finland is famed for its woodlands and lakes, indeed lakes cover almost 10% of Finland. 

Bombus bohemicus (c) Janne Heliola

Finland’s national pollinator strategy shares largely the same goals as the Scottish version, which was used as one source of inspiration in designing it. The strategy was formed by a steering group including the most essential stakeholder groups (administration, farmers, conservation organizations etc.), led by the Ministry of Environment. The strategy includes several measures to prevent a further decline in pollinator numbers, as well as a commitment to improve the nationwide monitoring of pollinators. Finland has already had an on-going monitoring scheme for both moths and butterflies since the 90s. As a result of the goals in the pollinator strategy, new monitoring has also been started on solitary bees and hover flies. There are strong similarities between this and the UK PoMS work.

The bumblebee monitoring in Finland was started in 2019 as a two-year citizen-science project. The expectations were rather low; a result of around 10-20 monitoring sites was thought to be realistic. Instead, the coordinators were astonished by an unprecedented popular and media interest on bumblebees and their monitoring. The number of sites reached 70 in the first year alone, and continued to increase. As the pilot proved to be a resounding success, it was continued for further years.

Bombus semenoviellus (c) Janne Heliola

The coverage in bumblebee monitoring, rather like in Scotland, tended to be geographically concentrated. Whereas the central belt sees most Scottish monitoring, it was the south of Finland that saw the greatest number of records submitted. 

As few volunteers had previous experience in identifying bumblebees, they were allowed to record them on a level which suited their knowledge. Thus for some recorders it was sufficient to note at least a part of their observations simply as bumblebee spp, whereas others gave either species group or indeed individual species information.

Most of the bumblebee transects walked have been around 500 to 1000m long. Records were submitted online. In the first three years 125 transects were covered, and in total over 55,000 bumblebees were recorded. As the coordinators expected, the proportion of bumblebee individuals identified on species level has steadily increasing during the first four years of the monitoring. This proves that although most of the recorders were amateurs to begin with, they have increased their skills through practice and produce more detailed information each year.

The species with the most individual records was the white-tailed bumblebee (Bombus lucorum), followed close by the common carder (B. pascuorum). The tree bumblebee (B. hypnorum) provide the third highest number of individual precise records. The number of species per site has usually been around ten, with some over fifteen at the most diverse locations. The monitoring has already shown that some species that have only recently colonized Finland, e.g. B. schrencki and B. semenoviellus, have already spread quite widely in the country.

We wish our Finnish counterparts good luck with their pollinator strategy, and look forward to carrying further news of their monitoring efforts over the years.

Further reading:

Bumblebee species on red clover in central Finland by PENTTI HÄNNINEN

With sincere thanks to Janne Heliola of the Finnish Environment Institute for all of his help in compiling this article.