Thorny issues

By Athayde Tonhasca

Once upon a time, so Charles Perrault (1628-1703) told us, a prince was out enjoying nature by merrily killing animals in the woods, when he spotted a hidden castle deep in the forest. The prince’s myrmidons explained that the castle housed a beautiful princess who had been cursed by an evil fairy; the young lady was to lay in a comatose state until awakened by a handsome prince. His Highness, who obviously had a high opinion of his looks, decided he was the person destined to break the spell. But getting to Sleeping Beauty wouldn’t be easy; the castle was surrounded by trees and a formidable obstacle that would have stopped a less determined hobbledehoy: a wall of brambles.

Having princely clothes ruined by brambles. The Sleeping Beauty, art by Arthur Rackham (1867–1939), Wikimedia Commons.

Brambles or blackberries comprise many species that are difficult to tell apart; over 300 of them have been recognized in the UK. These related species are known as micro-species, and for practical reasons they are treated collectively as a species complex or as an aggregate group (abbreviated as agg.). So we usually refer to brambles as Rubus fruticosus agg.

Natives to much of Europe, brambles are valued fruit crops when grown as blackberry varieties, but they are also invasive in some circumstances. Their dense thickets are barriers to amorous princes and roaming livestock, and their thorns hurt animals and contaminate wool. Thanks to their vigorous growth (watch their shoots thrusting ahead), brambles can outcompete other wild plants and curtail the development of tree saplings; if left unchecked, brambles can quickly alter the species composition and physical structure of some habitats. For those reasons, they are considered invasive weeds in Australia, New Zealand and the USA.

But as we have learned from many a definitive self-help book, problems are opportunities with thorns on them: several birds and small mammals nest or take shelter in bramble scrub. And their berries are food for sundry animals such as badgers, field mice, foxes, moths and voles: watch some of them having a nutritious fruit breakfast. Bramble berries are quite handy when other sources begin to dwindle in late summer and autumn.

A bramble thicket: barrier and shelter © Richard Humphrey, Wikimedia Commons.

But brambles have much more to offer; their open, bowl-shaped flowers, typical of the Rosaceae family, are easily accessible and produce large amounts of pollen and nectar, which are available during most of the season – usually from May to September in the UK. So a range of pollinators and other insects take advantage of these abundant and reliable food sources, from the European honey bee (Apis mellifera), which is one of the most enthusiastic visitors, to scarce species such as the brown-banded carder bee (Bombus humilis) (Wignall et al., 2020).

A welcoming bramble flower © Rosser1954, Wikimedia Commons.

Brambles have a flexible approach to reproduction. They commonly propagate vegetatively (no seeds are involved) by deploying ‘runners’, shoots that take root when they are touching the ground; they can resort to apomixis, which is the production of seeds without fertilisation; or less frequently, they can use the familiar sexual mechanism of pollen deposition. This diversified strategy helps explains brambles’ complex taxonomy. Plants generated by vegetative growth or apomixis are clones, genetically identical to the parent plant. When they do occasionally outcross and produce seeds from fertilized ovules, the resulting offspring will have genetic profiles slightly different from the parent plant. Given time, these variants become species marginally different from each other, which spread out as clones and readily hybridise (Clark & Jasieniuk, 2012). Untangling these species is a job for a small tribe of patient, dogged taxonomists dedicated to batology (from the Ancient Greek báton, ‘blackberry’): the scientific study of plants in the genus Rubus.

Although infrequent, sexual reproduction is important for maintaining brambles’ genetic diversity, and here insects play their part by cross-pollinating plants. Among brambles’ many flower visitors, several bees and flies have been considered candidates for the job. But this list is biased because it leaves out insects we don’t normally see collecting pollen or nectar – the nocturnal visitors, i.e., moths. And they should not be neglected. Like many other plants, brambles produce nectar with variable concentrations of sugars during the day, and their highest output happens to be from late afternoon into the evening. Such sugary bounty wasn’t likely to go unnoticed by the night shift wanderers. Anderson et al. (2023) reported a range of visitors to brambles flowers during the day (flies and bees, mostly); but at night, moths were almost alone in dropping by for a sip of nectar. But there was more; moths visited fewer flowers per hour than diurnal visitors, but they deposited more pollen grains on stigmas. That’s an important finding. Flower visitation is often – and incorrectly – associated with pollination. In fact, some visitors avoid pollen altogether, or manage to remove the pesky yellow grains from their bodies. Pollen deposition is a well-tested method to evaluate who is pollinating what.   

A tobacco hornworm (Manduca sexta) depositing pollen on a Colorado Springs evening primrose flower (Oenothera harringtonii) © Smith et al., 2022.

So here we are. Blackberry lovers notwithstanding, brambles are generally despised components of our flora, even though they play an important part in supporting pollinators and other animals. These brambles’ customers in turn may depend on secretive moths for the sexual reproduction of their hosts. As is often the case in nature, the plot is considerably thicker than it looks.

Among the brambles, by Valentine Cameron Prinsep (1838–1904), enjoying luscious berries © Stephen Craven, Wikimedia Commons.

A hard flower to crack

By Athayde Tonhasca

Brazil nuts are high up in the list of superfoods, a gimmicky but highly profitable market. For some internet gurus, the nuts protect you against inflammation, heart disease, diabetes and cancer; and, inescapably as superfoods go, they are loaded with ‘antioxidants that fight free radicals’ – a scientifically baseless but commercially catchy label. Hype aside, Brazil nuts are highly nutritious: they are loaded with proteins, carbohydrates, unsaturated lipids, vitamins and essential minerals such as calcium, magnesium, phosphorus and potassium. But their main claim to fame is to be one of the best sources of selenium, an essential element for a range of metabolic processes in our bodies. These nuts have their detractors because of the unlikely risk of selenium poisoning for those who over-indulge in them, and the danger posed by aflatoxins (carcinogens produced by certain fungi) when the nuts are not stored properly. The healthy aspects of Brazil nuts are clearly winning over the popular perception because the European and American markets keep growing steadily. Which is good news for the main nut producers Bolivia (the world’s major exporter), Brazil and Peru.

Assorted nuts, essential while watching a match on the telly © Melchoir, Wikimedia Commons.

The nuts are in fact seeds extracted from the hard, coconut-like fruits produced by the Brazil nut tree (Bertholletia excelsa). Named excelsa (high, exalted, lofty) by naturalists and explorers Alexander von Humboldt and Aimé Bonpland, this is one of the tallest trees in the Amazon region. Some individuals reach heights of 30 to 50 m, with trunks of 1 to 2 m in diameter – up to 5 m in older specimens. And they can live long lives: radiocarbon dating has identified some 800- and 1000-year-old trees (Camargo et al., 1994).

Brazil nuts are gathered from fruits fallen to the forest floor during the rainy season. The work, carried out by native people and small farmers, has one serious risk: the thick-walled fruit of the Brazil nut tree is 10-15 cm in diameter and weighs on average 750 g. A fruit of this size falling from about 7 m generates sufficient kinetic energy to fracture a skull and cause severe to fatal injuries (Ideta et al., 2021).

A Brazil nut fruit and seeds in their shells, and seeds ready for the market © P.S. Sena and Quadell, Wikimedia Commons.

Brazil nuts are harvested almost entirely from wild trees because tree cultivation has been largely unsuccessful. One of the reasons for the failure to turn the tree into a farm commodity is its pollination requirements.

The Brazil nut tree reproduces by cross-fertilisation, but its flower is not the run-of-the-mill, pollinator-friendly structure found in most plants. It has a curled extension – called a ligule – that forms a hood over the petals, which are pressed together like an inverted cup. Ligule and petals create a chamber that conceals stamens, stigma, and the nectaries. To access the nectar, an insect has to squeeze itself between the ligule and the tightly packed petals. If successful, the visitor may come out dusted with pollen and transfer it to another flower.

The inflorescence of a Brazil nut tree © Scott Mori, The New York Botanical Garden, Lecythidaceae – the Brazil nut family.

The flowers of the Brazil nut tree receive many visitors, including hummingbirds, moths, butterflies, beetles, and several bees. But getting into a flower for its nectar is not for the nimble or weak; only the largest and strongest bees can lift the ligule to reach the reproductive organs.  This select heavy-weight club includes bumble bees (Bombus spp.), Centris spp., Epicharis spp., orchid bees (Eulaema spp.), and carpenter bees (Xylocopa spp.). 

An E. meriana orchid bee (L) and a large carpenter bee (X. mexicanorum), two of the robust bees capable of handling a Brazil nut tree flower © Insects Unlocked, Wikimedia Commons.

In the central Amazon rainforest, the orchid bee E. mocsaryi and carpenter bee X. frontalis are especially important Brazil nut tree pollinators because of their abundance and frequency of flower visitations (Cavalcante et al., 2012). Watch X. frontalis hard at work. 

An E. mocsaryi orchid bee forces itself between the ligule and the tightly packed petals of flower of the Brazil nut tree © Cavalcante et al., Wikimedia Commons.

The large bees that pollinate the Brazil nut tree can fly long distances, which is important for maintaining its genetic diversity: trees typically grow in groups of individuals that are isolated from each other in the forest. These bees are solitary or semi-social, and none of them have been domesticated; so their survival depends on the natural habitats that supply nesting sites, food – one type of tree alone will not provide for the whole season – and other resources such as orchid fragrances, which are collected by male orchid bees.  

Other characters play an important part in the life of a Brazil nut tree: rodents. The fruit capsule is too hard for most animals that could be interested in the nutritious seeds – but not to agoutis (Dasyprocta spp.). Thanks to their powerful teeth, they can gnaw their way to the seeds. Sometimes an agouti can’t eat all the seeds at once, so the prudent animal takes them some distance away (up to 20 m) and buries them as a food reserve for leaner times. But it so happens that the agouti’s memory is not the sharpest; it often forgets the way back to the food cache. Or the agouti itself may become a meal for a large cat before returning to its seeds. Either way, the buried seeds germinate. This unintentional planting by agoutis, pacas (Cuniculus spp.) and the southern Amazon red squirrel (Sciurus spadiceus) is the only route to seed dispersal for the Brazil nut tree, thus is vital for its survival. Follow the exploits of a forgetful agouti in the forest.

A red-rumped agouti (Dasyprocta leporina) © Alastair Rae, Wikimedia Commons.

As one can imagine, these required interactions with bees and rodents don’t bode well for the future of the Brazilian nut tree. Amazonian ecosystems have been eroded away by the relentless march of deforestation and land conversion to agriculture and pastures. To make things worse for the tree, its wood is highly valuable (its felling is illegal, but that doesn’t stop illegal loggers). One of the consequences of the devastation is the increasing scarcity of Brazil nuts in Brazil, which helps explain why Bolivia took the lead as the main exporter. 

We may take the hard-nosed view that we can’t do anything about the plight of the Brazil nut tree, but that’s not quite right. One could be inquisitive and demanding about the origin of a nice piece of hardwood furniture for sale, or the juicy steak in a restaurant or supermarket freezer (much of exported South American beef comes from deforested areas). Or we could accept a life without Brazil nuts: after all, to us they are just comfort food. But the tree’s demise could be a portent. In the 1980s, doomsday prophet Paul Ehrlich and his wife Anne Ehrlich famously compared species’ roles in an ecosystem to rivets in an aeroplane’s wing. Aircraft manufacturers use more rivets than necessary to affix the wings, so removing a few of them would make little difference. But if they continue to be taken away, at some point a critical rivet is lost, and the aeroplane will crash. Similarly, how many species can you lose before an ecosystem fails? We don’t have an answer for that, or even know whether the Ehrlichs’ model is realistic. The eventual loss of the Brazil nut tree could be just one redundant rivet popped out of the body of biodiversity; or it could be a warning of bad things to come to bees, agoutis, the forest and its peoples, and, at the end of the queue, to us, sophisticated Brazil nut munchers. 

The Brazil nut tree is the symbol of the Amazon Forest. Its size makes it difficult to capture it whole in a photo © upper left: My Favorite Pet Sitter; lower left: mauroguanandi; rigth: Edsongrandisoli, Wikimedia Commons.

Helping hands

Today we are delighted to publish a guest blog by our good friend Anthony McCluskey of Butterfly Conservation Scotland. Anyone who has heard Anthony deliver one of his excellent talks will know that he is a man of many talents and a most persuasive naturalist.

Besides being beautiful and charming parts of our native biodiversity, butterflies and moths are extremely important in ecosystems. They aren’t well-known as pollinators as they (mostly) don’t eat pollen the way bees do and only tend to pick up pollen incidentally when they’re drinking nectar. Yet even more importantly, the adult insects and their caterpillars are vital for the diets of vertebrates like bats and birds, and a typical nest of blue tits can consume upwards of 30,000 live food items like caterpillars for one brood.

Lennoxtown Meadows

But work to help these insects will also benefit a huge range of other insects, including bees, beetles and bugs. This became clear to me during the Helping Hands for Butterflies project, which was a three-year Butterfly Conservation project funded by the National Lottery Heritage Fund and NatureScot, and which concluded in September 2022. 

Through the project, I worked with volunteers to create and maintain nine new meadows in parks across central Scotland, including in Glasgow, Edinburgh, South Lanarkshire and Lennoxtown. 

The aim was to boost local butterfly populations in these parks. In order to do this, it’s important to have food for their caterpillars. In Scotland we have 35 species of breeding butterflies. If we disregard the rarer, habitat specialist species, and those whose caterpillars feed on trees and shrubs or nettles (not normally planted in meadows on purpose!) we are left with about only 12 species. Of these 12, five are ‘brown’ butterflies such as Ringlet and Meadow Brown, whose caterpillars feed only on various grasses. A further three were the ‘white’ butterflies such as Green-veined White and Orange-tip, whose caterpillars would feed on Cuckoo-flower.

So instead of turning over the ground or killing the grass off with herbicide, we decided to simply try to make existing amenity grassland more diverse, as the ‘grass’ part of the grassland is clearly important for many butterfly and moth species.

Enjoying Stonefield Park, Blantyre

Work was started in October 2019, and at all sites we started by sowing Yellow Rattle into established amenity grassland after scratching the grass surface to reveal the soil then trampling the seeds in. The following summer (during the height of the Covid-19 pandemic), Yellow Rattle bloomed and did a great job in supressing the growth of grasses as it as a natural parasite of grass roots. That autumn we got the council staff to cut the meadows, and we came along to remove the grass clippings. In most cases we were able to drag these off to small woodlands in the parks where the decomposing grass would feed the growth of trees. This step is very important, as repeated cutting and lifting will reduce the vigour of grass and allow more wildflowers to come up. 

Following this we got to work planting wildflower plug plants of key nectar-rich plants to benefit adult butterflies and moths. My top recommendations for these fall into three categories: Tall plants (Common Knapweed, Field Scabious and Red Campion) which can all grow quickly and get their heads above the grasses; Scrambling plants (Bush Vetch, Meadow Vetchling, Common Vetch) which have tendrils and can climb over grasses; and finally Tough plants (Red Clover, Yarrow) which just seem to hold their own. I also included Common Bird’s-foot Trefoil – this pretty wildflower is important in meadows as it’s the foodplant for the Common Blue Butterfly and Six-spot Burnet Moths, and many others besides these. Cuckoo-flower was also included as it’s important for three of the widespread white butterflies. 

We carried on in this pattern for the rest of the project, with a total of three rounds of cutting and lifting, one round of Yellow Rattle Sowing (as it sowed itself back into the sites each year) and two rounds of plug planting.

Elder Park, Glasgow

I am pleased to say that after three years of work, breeding butterflies were found at eight of the nine new meadows, and moths were found at all of them! One of the best was Springburn Park in Glasgow. The site there is quite damp and already had small patches of Cuckoo-flower (which prefers damp soil). Within two years we found good numbers of both Meadow Brown and Ringlet butterflies – species whose caterpillars eat vigorous grass like Cock’s-foot and Yorkshire-fog.

It was especially exciting to find Small Heath butterflies there too as populations of this species have halved in the last 50 years. White butterflies like Small White, Green-veined White and Orange-tip were attracted in by the cuckoo-flower which could finally put up its flower stalks after years of being cut back when the grass was kept short. Even on wet days it was possible to confirm their presence in the meadow, as their eggs are easy to find on the leaves and flower-stalks of the plants. 

Silverknowes Park meadow

We mustn’t forget moths though, and one of my favourite finds was the Large Yellow Underwing. The first clue that this species was breeding in the meadow at Stonefield Park in Blantyre (and others) was the presence of large parastic wasps which were likely of the Amblyteles armatorius species. I found these wasps in June, flying through the meadows looking like they were searching for something. Turns out they were – they hunt large caterpillars (especially those of Large Yellow Underwings) to lay their eggs into! Bad news for the caterpillar, but good to see more insect diversity. When I visited again in August as part of a Meadow Discovery Day I was running, I could occasionally see large orange-coloured insects flying up from the meadow as people walked through. But one of the children on the walk had been given a net, and he managed to catch one – a Large Yellow Underwing! 

So if I was to summarise this approach to will help encourage more butterflies in established greenspaces, it would be three simple steps:

Let the vegetation grow all summer, and only cut and lift it from September onwards.

Sow Yellow Rattle early on – but ensure it gets sown in the autumn or winter, and seeds make good contact with bare soil.

Plant wildflower plug plants of nectar-rich plants like Knapweed, Red Clover, Vetches, Cuckoo-flower and Bird’s-foot Trefoil.

Ruchill Park, November 2021

Bees and other pollinators will have gotten a boost from these meadows too, as they all contain more nectar- and pollen-rich wildflowers. It was also really encouraging to hear grasshoppers at all of the sites, and see a huge range of plant bugs and find lots of ladybirds chomping on the aphids. 

In one of the parks, the new meadow was the only place I could find bees feeding when I visited, which was a stark reminder that most of our parks and public greenspaces have a long way to go. Yet I see this as an opportunity to transform hundreds more acres of public land for insects, and hope that more people will start doing the same!

You can find all the resources created for the Helping Hands for Butterflies Project on our webpage, including more detailed guides on butterfly caterpillar foodplants and the final evaluation report.

With thanks to National Lottery Heritage Fund and NatureScot for funding the project, and to City of Edinburgh, Glasgow City, South Lanarkshire and East Dunbartonshire Councils for making the land available for these meadows, and contribution of staff time and resources.

Pollinators with bad PR

By Athayde Tonhasca

When member of the serial killer community ‘Buffalo Bill’ decided to leave a message to his FBI pursuers, he stuffed the pupa of a black witch moth (Ascalapha odorata) down the throat of his last victim (The Silence of the Lambs, by Thomas Harris). Buffalo Bill may have been a psychopath, but he knew his insects: a target for superstition and ignorance, the black witch is considered a harbinger of doom in many countries. But the makers of the film version of Harris’ story wanted something even more dread-inducing: they substituted the black witch for the African death’s-head hawk moth (Acherontia atropos), another species with a long tradition of spookiness. 

An African death’s-head hawk moth © Muséum de Toulouse, Wikimedia Commons.

With a bit of imagination, you can see a human skull on the moth’s thorax, a feature that has tied the harmless creature to all sorts of legends and misconceptions. Starting with its name, A. atropos, and the names of the other two death’s-head hawk moths from Asia,  A. lachesis and A. styx, which are homages to Greek myths about mortality.

Atropos and Lachesis were two of the three Moirai, the goddesses of destiny, and Styx is the river that divides Earth from the underworld. Adding to the African death’s-head hawk moth’s capacity to awe and alarm, it can chirp when disturbed. You can listen to it here (volume up!) 

The three Moirai, by Alexander Rothaug (1870-1946).

Artists and writers have been inspired by the hawk moths’ mystique, from Edgar Allan Poe, John Keats and Bram Stoker, to stories about its nefarious influence on the mental health of King George III. The University of Cambridge’s Museum of Zoology holds a specimen taken from the king’s chambers by one of the royal physicians.

Dracula, by Bram Stoker (1847-1912), 1919 edition © British Library, image in the public domain.

All these loopy tales distract us from the tangible facts about the death’s-head hawk moth. Which is a pity, because this species is remarkable in many ways. It migrates seasonally from Africa to southern Europe, venturing now and then north of the Alps and into Britain, sometimes as far as the Shetlands, from August to October. The moth travels at night for up to 4,000 km, maintaining a straight path by adjusting its flight plan according to wind conditions. How do we know that? By fitting moths with miniscule transmitters and following them in an aeroplane (Menz et al., 2022). 

The moth’s large, unmistakable caterpillars feed on potato-related plants (Solanum spp.), and can be abundant in potato fields during years of high migration. The feeding habits of adults are less well known. Most adult hawk moth species have an extended proboscis suitable for taking nectar from flowers with long corollas. But the death’s-head’s proboscis is shorter, and it cannot reach the nectar of many flowers. So it adds to its diet by feeding on rotting fruit, tree sap, and, remarkably for a moth, honey. The death’s-head sneaks into colonies of honey bees (Apis spp.) to pilfer their honey – thus the moth’s alternative epithet: ‘bee robber’. It manages to survive such a daring raid thanks to chemical camouflage: moth and bees share some of the cuticular hydrocarbons that bees use to identify nestmates. The moth’s short legs and stout body also help it wiggle in and out of the hive. But these ruses don’t work all the time: beekeepers often find moth remains in their hives.   

A death’s-head hawk moth caterpillar © Erik Streb, and imago (adult stage) © Stahre, Wikimedia Commons.

The death’s-head hawk moth is a poor pollinator candidate, even though we know little about its ecology. At a first glance the other 1,400 or so hawk moths, also known as hummingbird moths, sphinx moths or sphingids (family Sphingidae) – mostly from Africa and the Americas – don’t look promising either. They don’t have pollen-carrying apparatus, and most of them are very good at keeping their distance from flowers. They usually feed by hovering in front of a flower, probing it with their straw-like proboscis. Hovering, a trait shared with hover flies, hummingbirds and some bats, is an energy-demanding flight mode, but it allows the moth to dart from approaching enemies and stay clear of spiders, frogs and other predators lurking on the flower. 

A convolvulus hawk moth (Agrius convolvuli) © Charles J. Sharp, Wikimedia Commons.

Plants however tell a different story. Flowers visited by hawk moths have characteristics that meet their visitors’ needs: in general, they open at night, produce copious volumes of sugar-rich nectar, are of white or pale colours, have long nectar tubes, and lack unnecessary landing zones. This fine-tuning between hawk moths and plants suggests adaptations for sphingophily, or pollination by hovering moths (a development from phalaenophily, which is pollination carried by flower-alighting moths). For plants, a smaller pool of specialised nocturnal visitors has the advantage of reducing the chances of pollen transfer between the wrong species. As a result, many plants are pollinated by hawk moths, of which certainly the most famous is the Darwin’s orchid (Angraecum sesquipedale). 

Two species pollinated by hawk moths: the greater butterfly-orchid (Platanthera chlorantha) © Jörg Hempel, and jasmine tobacco (Nicotiana alata) © Carl E Lewis, Wikimedia Commons.

Hawk moths are among the strongest flying insects; some are capable of commuting for several kilometres in search of flowers, sustaining speeds of over 19 km/h. They may carry only a few pollen grains attached to their proboscis or other body parts, but this pollen can be dispersed over large areas, which is advantageous for plants’ genetic diversity. Long-distance distribution may reduce the impacts of habitat fragmentation, which is the inevitable result of human occupation of natural areas. Indeed, Skogen et al. (Annals of the Missouri Botanical Garden 104: 495-511, 2019) showed that pollen dispersal by the white-lined sphinx or hummingbird moth (Hyles lineata) promotes gene flow between populations of the endemic Colorado Springs evening primrose (Oenothera harringtonii). You can watch hawk moths at work here.

A white-lined sphinx © Larry Lamsa and Colorado Springs evening primrose © Juanita A. R. Ladyman, Wikimedia Commons.

The role of moths as pollinators is poorly understood, but this gap in our knowledge is understandable. It is not easy to study pollination in daytime: at night, data collection is downright difficult. But we are learning more and more about moths’ contribution to the pollination of wild plants and crops. Nocturnal moths comprise around 90% of the 180,000 or so known species of Lepidoptera, so there is much to be discovered about busy but secretive hawk moths. 

The Hireling Shepherd, by William Holman Hunt (1827-1910). The cheeky shepherd boy shows a death’s head hawk moth to the girl, who looks unimpressed.