Loving a cold climate

At this time of year I try to make a trip to Perthshire’s Ben Vrackie. Truth be told it’s a fairly unspectacular mountain.  Neither too long or difficult a climb, occasionally a wee bit busy, it fits the bill for a short day rather than an epic outing amongst the hills.  Nonetheless, it has a ‘hidden’ allure that belies its familiarity.  It offers beautiful views, and, here’s the clincher, it’s a great place to see purple saxifrage.

Purple saxifrage (Saxifraga oppositifolia) is a good indicator that spring is rolling in. It  also has that ‘Location, Location, Location’ appeal. Given its preference for the uplands it connects with hill-walkers in the same way that a glimpse of other mountain specialists such as golden eagles, dotterel or dashing mountain hares lift the spirits.  

With tightly-knit rosettes of small, vivid pinky-purple flowers, purple saxifrage is a prostrate beauty which can add a splash of dense and welcome colour to what are often otherwise monochrome days.

It’s a tough wee critter too.  Those purple flowers, each with five petals, withstand punishing conditions from perishing sub-zero temperatures to howling gales. 

That hardy quality means this is truly a plant at home in the mountains.  You will find it in some of the coldest areas of Northern Europe and beyond. Apparently, it has been recorded at 4,500 metres in the Swiss Alps. 

This begs a question. ‘How does a plant which emerges before the bulk of our pollinating insects achieve pollination in such a forbidding setting?’   

The answer lies with flies. Not those mesmerising, boldly coloured, hoverflies which we often see in our parks and gardens, but rather in ordinary looking dull black flies related to house flies. 

In mountain situations, above the altitude where heather is abundant, and in more northern parts of the world these types of flies are often successful pollinators.

The combination of cool, windy weather and a relatively low number of flowering plants creates a difficult environment for bees which have a relatively high energy requirement for themselves and their brood. And bees which favour higher ground, such as monitcola, are still in hibernation come early spring.

On the other hand, many of our upland-based flies over-winter as adults in sheltered spots amongst nooks and crannies in rocks. From there they can dash from their ‘cosy’ resting state relatively quickly if the weather warms up just a little. Thus they are on the wing before bees emerge, and they rely on the likes of early flowering saxifrages as a nectar source.

In an environment where the weather is often highly changeable these pollinating flies also ride out bad weather by retreating and finding temporary shelter. Thank goodness they do, for we depend on these little, rather obscure, insects to pollinate many of our specialised mountain plants, including our beautiful purple saxifrage. 

The appeal of purple saxifrage is widespread. Not only is it admired in the far north of Europe and the Alps, it’s the national flower of Nunavut, a huge northern territory in Canada. Closer to home, there is a record showing it spotted at 1,210 m on Ben Lawers and I once read an update celebrating that it had been found flowering on Snowdon on 26 January. Amongst Yorkshire walkers, purple saxifrage can enliven a spring trip to Pen-y-ghent or Ingleborough. Dip into the Cairngorm Club journals and mentions of purples saxifrage are not hard to find.

Scotland is the British stronghold for this botanical gem. Draw a line on a map, roughly from Greenock to Brechin, and north-west of that line you’ll find plenty of places to see purple saxifrage. Luckily for me Ben Vrackie is one of them, and it’s an annual delight to see this spectacular and hardy little plant confirm that spring is here again.

Find out more:

Botanical Society of Britain and Ireland on purple saxifrage

The RHS purple saxifrage introduction

Menacing tenants

By Athayde Tonhasca

In an apple orchard somewhere in the American state of Pennsylvania, an adult Japanese horn-faced bee (Osmia cornifrons) has just emerged from its nest and makes its way into the big wide world. The apple grower has high hopes for that bee; in fact, he bought many of them when they were still inside their cocoons. The Japanese horn-faced bee was introduced from Japan in the 1970s, and since then it has been widely used in the Eastern United States to improve the pollination of apples and other fruit trees such as peaches, pears and cherries.

A female Japanese horn-faced bee © Chelsey Ritner, Exotic Bee ID.

In their natural habitats, the Japanese horn-faced bee and similar species such as the red mason bee (O. bicornis) nest inside natural cavities such as hollowed reeds, tree holes and cracks in stones. Females use a range of materials, especially mud and pebbles, to build individual nest cells in which they lay an egg. When bees are done, they seal off the nest entrance with mud – so they are known as mason bees. Fruit growers offer bees nesting alternatives such as drilled blocks of wood or bunches of cardboard tubes tightly packed together.

Two types of mason bee nests used in orchards: cardboard tubes (a) and wood blocks (b). Pictures by N. Joshi © Kline et al., 2023.

The future seemed promising for that Japanese horn-faced bee in Pennsylvania. But opportunists were on standby, ready to pounce when an unsuspecting bee leaves its nest. In the blink of an eye, a gang of hypopi (singular hypopus) jumps on the bee, holding on for dear life as their ride flies away.

Hypopi, also known as hypopodes, are a special nymphal stage found in some mites. In this case, the hairy-footed pollen mite (Chaetodactylus krombeini). Hypopi have no head or mouthparts, but are armed with special structures for hanging on; either powerful claws or a sucker plate to glue themselves to their host. These adaptations greatly facilitate phoresis, which is when an organism attaches itself to another for the purpose of transportation. Phoresis is typically found in small and poorly mobile organisms such as nematodes and mites. But curiously, the hypopus stage is usually facultative for mites; it occurs only when conditions deteriorate (food scarcity, overcrowding, dry climate, etc.), so that skedaddling increases the likelihood of survival.

A hypopus, the stage adapted for phoresis © Reynolds et al., 2014.

The departing bee has no chance of avoiding the lurking hitchhikers who react instantaneously to the slightest touch to their dorsal setae (bristles) or to air movement caused by a passing body. And the feats of some of these mites defy credulity; the tiny Histiostoma laboratorium (formally known as H. genetica), a scourge of vinegar fly (Drosophila melanogaster) laboratory colonies, lurches into the air to grab fruit flies flying above them (Hall, 1959. J. Kansas Entomological Society 32: 45-46). Some species that have hummingbirds as hosts rush to the birds’ nostrils at a rate of 12 body-lengths per second, which is a speed similar to a cheetah’s (Colwell, 1985)

Hypopi attached to their host © D.E. Walter, Invasive Mite Identification, Colorado State University and USDA/APHIS/PPQ Center for Plant Health Science and Technology.

After being mobbed by hypopi, the bee carries on with its life. If it’s a female, she will mate and start a nest of her own. When her brood cells are ready, her unwanted companions come out of their lethargic state, jump off and resume their development, maturing and reproducing very quickly, all the while feeding on the pollen and nectar gathered by the bee. When their numbers reach certain levels, they may feed on the bee’s eggs and larvae (details are sketchy). In a few months the mites may reach thousands and overrun the brood cell, leaving space for nothing else.

Hairy-footed pollen mites inside a mason bee nest cell © Pavel Klimov, Wikimedia Commons.

Such massive numbers of kleptoparasites (organisms that steal food from another one) spell serious trouble for Japanese horn-faced bees; their eggs and larvae die or develop poorly for lack of food or direct attack from mites. Some adult bees may not even have a chance to start a new family; they may be so burdened by mites that they cannot fly. They fall to the ground and become easy pickings for ants and other predators.

A mason bee loaded with pollen mites © GeeBee60, Wikimedia Commons.

Several mason bee species are susceptible to the hairy-footed pollen mite, but managed Japanese horn-faced bees have been hit particularly hard, with losses reaching up to 50% of the population. It’s not difficult to understand why. The same way slum housing conditions make people more vulnerable to all sorts of diseases, jam-packed nests increase the chances of mites passing from one bee to another. And the hairy-footed pollen mite does not even depend on phoresis: adults can walk from one nest to another nearby, getting inside through holes in the sealing mud made by parasitic wasps. To make the situation worse, this mite can turn into a dormant stage that survives several years inside an empty nest, rousing back to activity as soon as new tenants arrive.

The effects of the hairy-footed pollen mite on the Japanese horn-faced bee are a reminder of the unintended consequences of well-intentioned actions. Bee houses or bee ‘hotels’ have been promoted as enhancers of wild bee populations, but there’s no indication of such effects. They do however increase the risk of pathogens and parasites: not only mites, but a range of fungi, parasitic flies and wasps bedevil mason bees (Groulx & Forrest, 2017).

A bee hotel: not such a great idea © Colin Smith, Wikimedia Commons.

American fruit growers do their best to keep mites under control by replacing the nesting tubes yearly, sterilising wood blocks, or removing and storing bee cocoons during the winter. If you have a bee house but don’t have the resources, time or inclination to do the same, you should follow Colin Purrington‘s advice: buy a garden gnome instead.

Glasgow’s engineering shift

Glasgow, Scotland’s biggest city, is affectionately nicknamed as the ‘dear green place’. It’s a long-standing label the city is proud of, and the city retains a special fondness for its many green spaces.  So much so, that Glasgow City Council implements its own Pollinator Plan.

The existence of a well-crafted and carefully thought through plan ensures a sustainable vision in creating pollinator-friendly habitat. Of course, a pollinator plan isn’t a ‘create, launch and walk away’ project. It’s a commitment, a durable framework, for ensuring that the conditions are created and then managed to ensure pollinators can prosper in a sympathetic urban setting. 

Readers of our annual Pollinator Strategy Progress Reports will be familiar with the fact that Hogganfield Park Local Nature Reserve and the iconic Queen’s Park are now designated Pollinator Parks and embrace Glasgow’s enthusiastic improvements for nature. They are rightly viewed as examples of work well-delivered; a bold visual and environmental break with an historically heavy industrial past.

Quality greenspaces aren’t of course the only thing Glasgow is famed for.  Once renowned for shipbuilding, tenements and engineering, Glasgow has gradually been crafting an alternative vision.  This is after all the home of Scottish Opera and the Burrell Collection, the city that hosted a solo show by artist Banksy, a vibrant urban centre with fantastic architecture and revamped river front.  In short, an evolving blend of attractions means that there is more to Glasgow than a busy industrial past, and the Pollinator Plan was just one more piece in an ever-diverse jigsaw. 

Last year the impetus for a better future for pollinators in Glasgow was maintained. Successful examples abound. Six meadow sites across the city are now managed by a well-briefed contractor to ensure that 17 hectares are sympathetically managed for wildlife. What’s more The Conservation Volunteers manage a further five meadow sites with a mixture of enthusiasm and expertise that makes the likes of Cathkin Braes Local Nature Reserve and Springburn Park sites to be proud of.

The numbers behind the Glasgow operation are impressive. Last year around 22,000 small bulbs and 16,500 wildflower plugs were planted across swathes of the city’s greenspaces amounting to 5500 square metres. A whopping quarter of a million daffodils were planted city wide. But perhaps the pièce de resistance was the successful move to create seven new meadows. 

It probably helps that the council have hung onto Pollok Country Park’s nursery.  Flower power and volunteer support are to the fore here and the legacy is growing – last year 28 Hub training participants carried out 42 volunteer hours seeding and caring for nursery.

It pays to have an open mind and a welcoming nature. 

Glasgow’s green aspirations have in the past included welcoming Butterfly Conservation to run a ‘meadow creation and maintenance’ workshop at Kelvingrove. The same organisation has also helped the famously friendly city host ‘meadow discovery days’ at Ruchill, Springburn and Elder Parks, introducing people to the plants and insects found in urban meadows.

Bumblebee Conservation Trust are another valuable ally. They co-ordinated nine Beewalk transects last year and supported a new addition to their ranks of Beewalks at Hamiltonhhill Claypits LNR.

And Hamiltonhill Claypits is a good place to end our story. Opened in the summer of 2021, this local nature reserve boasts wooded walks and paths alongside the once bustling Forth and Clyde Canal, in North Glasgow. It’s fine example of what was once an industrial hub transforming, over many years, into a place for nature and wildlife to thrive. That’s good news for pollinators, and good news for Glaswegians.

The useful interloper

By Athayde Tonhasca

Among the world’s myriad natural habitats, mangroves are not likely to be voted the most beautiful or inspiring. Mangrove forests consist mostly of monotonous swathes of twisted, stunted-looking trees with exposed roots that grow on harsh, muddy, hot shores of tropical and subtropical regions. Mangrove species thrive in these places because they are not put off by oxygen-starved, waterlogged mud; and they are halophytes, that is, adapted to saline or brackish water, conditions that would kill most plants.

A mangrove forest © Leon petrosyan, Wikimedia Commons.

Although mature mangrove plants don’t mind too little oxygen and too much salt, their seedlings would die or develop poorly is such environment. To get around the problems caused by inhospitable nurseries, mangrove species adopted the form of reproduction found in mammals, some reptiles and a few fishes: vivipary, which is embryo development inside the mother’s body. In the case of plants, the seeds germinate and develop into seedlings while still attached to the parent tree, which supplies water and nutrients to its offspring. When the seedlings – called propagules – are sufficiently mature, they drop and take root near the parent tree or float away with the tides to establish somewhere else. You can follow the amazing life cycle of the red mangrove (Rhizophora mangle).

Red mangrove cigar-shaped propagules about to drop into muddy waters © Katja Schulz, Wikimedia Commons.

You may not choose mangroves for a picnic or camping site, but their value should not be underestimated. By hugging the coast, mangroves are barriers against waves, forming a line of defence of increasing importance as the changing climate makes storms and flood surges more frequent and severe (watch a simulation of how mangrove forests protect the shoreline). Their dense, labyrinthine roots filter and purify the water, at the same time creating sediment deposits that reduce coastal erosion. Mangrove roots also act as nurseries for a large number of marine species, many of them vital sources of protein for low-income communities. These apparently impenetrable forests are safe havens for hundreds of plant and animal species, some of them rare and threatened. Although confined to warmer regions, mangroves have a global importance, especially because they absorb and store more carbon than tropical rainforests. Despite their value, mangroves are one of the most threatened habitats on the planet, encroached by coastal development and seafood farms.

Global distribution of mangrove forests © Pinpin, Wikimedia Commons.

Some mangrove species are pollinated by the wind or bats, but most require insects. Bees, ants, flies and butterflies have been identified as potential pollinators in different mangrove regions, but we have a poor understanding of these interactions – with at least one exception:  the European honey bee (Apis mellifera) has proven its credentials as an effective mangrove pollinator. 

The grey mangrove or white mangrove (Avicennia marina) is distributed throughout Africa and south-east Asia, and is the most common and widespread mangrove species found along the Australian coast. Dozens of insects visit this plant, but only the European honey bee has been shown to remove pollen from a flower and deposit it on another one (Hermansen et al., 2013), which are the necessary steps for plant fertilisation. This industriousness created a conundrum for Australian conservationists and policy makers.

Grey mangrove. Native Australians and European settlers use its light but strong wood for construction and boat building © Kahuroa, Wikimedia Commons.

Since its introduction to Australia in the 1800s, the European honey bee has made good use of the country’s favourable climate and extensive areas of native vegetation: it spread out quickly and widely. The bee’s seamless adaptation to its new habitat has created a bonanza for the thousands-strong Australian beekeepers, and for countless farmers who benefit from an efficient and reliable pollination service. But not all was well. 

Trees are the European honey bee’ ancestral habitats; before they became intensively bred and managed, honey bees nested in tree holes and collected pollen and nectar from tree canopies. When swarms escaped into the Australian wilderness, they readily went native by moving into tree cavities and ejecting – and sometimes killing – local residents like cockatoos, parrots, kingfishers, opossums and bats (Western Australia Museum). Feral European honey bees may also outcompete the 2,000 or so native bee species for food and nesting sites, and help spread weeds, pests and diseases. These impacts have been reported elsewhere, but in Australia the data are incomplete or inconsistent (Prendergast et al., 2022). The best we can say is that the interloper may interfere with a flora and fauna that have evolved together for millions of years.

European honey bees help sustain populations of grey mangrove in Australia, with substantial economic and ecological benefits; but these latecomers to the Aussie scene may also disrupt other species interactions and processes. Such dilemmas and uncertainties are nothing new in conservation: only hard work and good data can help us learn which way the balance tilts.

Grey mangrove flowers are irresistible to European honey bees © Dave Britton, Australian Museum