Lights-out, please

By Athayde Tonhasca

As the human population increases and concentrates more and more in cities, the world becomes more illuminated. Artificial light at night (ALAN) is an ever growing phenomenon because of the lighting of streets, parking lots, roads, buildings, parks, monuments, airports, stadiums – basically any manmade structure. This artificial light is scattered into the atmosphere and reflected back, particularly by clouds, creating a night-time sky luminance known as ‘sky glow’. Excessive illumination and artificial sky glow spread way beyond urbanized areas, essentially contaminating the whole landscape with light: night-time darkness is disappearing.

Sky glow over Kent © Chris Isherwood, Wikipedia Creative Commons

The Milky Way galaxy has awed civilizations and inspired many philosophical thoughts about mankind’s insignificance, our place in the big scheme of things, the fleeting nature of life, and what it’s all about. But if young Europeans or Americans are asked to share their impressions about the Milky Way, chances are the responses will be limited to a shrug or a puzzled look: the Milky Way is hidden from about 60% of Europeans and 80% of North Americans because of light pollution. When Los Angeles went through a blackout in 1994 because of an earthquake, emergency services received several calls from nervous citizens about a giant, strange, silvery cloud in the dark sky. These Angelinos were seeing the Milky Way for the first time.

The Milky Way, unseen by many © Creative Commons Attribution 3.0 Unported license

Light pollution is an ecological disturbance with multiple consequences. ALAN disrupts natural day-to-night rhythms such as singing and migration of birds, the activity period of small mammals, mating of frogs, nesting of bats and the orientation of sea turtle hatchlings. There is increasing evidence that humans are also sensitive to ALAN: it affects our circadian rhythm (the sleep–wake cycle repeated approximately every 24 hours), resulting in irregular hormone production, depression, insomnia and other maladies.

Insects couldn’t be immune to the effects of ALAN since much of their behaviour is dependent on light. We don’t know how insects see the world, but they recognize forms, detect movements and discern colours based on lighting patterns. Insects can monitor the position of the sun by the polarization of light, so they can navigate with precision. Light detection helps them to keep track of the photoperiod (day length), which is fundamental to preparing for the winter months. 

Many beetles, flies, lacewings, aphids, dragonflies, caddisflies, wasps and crickets are drawn to light, but moths’ compulsive and apparently suicidal attraction to lightbulbs or flames is the most familiar case of positive phototaxis (moving towards a light source) among insects. Moths are our better known nocturnal pollinators, so naturally their possible vulnerability to killer lights is a matter of concern.

© Fir0002, Wikipedia Creative Commons

It turns out that moths’ fatal attraction doesn’t seem to be that fatal because they are only drawn to light at relatively short distances. A few moths come to a blazing end, but most of them are beyond light’s dangerous pull. This is not to say that moths are safe from ALAN. When it’s not sufficiently dark, the production of sex pheromones and egg-laying are inhibited for some species, so that their reproduction is affected. Also, the window of time for courtship and mating can be severely reduced. Light pollution interferes with moths’ perception of colours and shapes, signals necessary for flower location. It also makes them more vulnerable to parasites and predators, either because they are easier to find, or their defence mechanisms (e.g., bat avoidance manoeuvres) are less effective in over-illuminated environments.

Light pollution disturbs many aspects of moths’ physiology and behaviour, although we can’t tell whether whole populations are being harmed: not all species respond equally, and there are many variables to be considered about the light source, such as wavelength, intensity, polarization and flicker. But from the little we know, excessive illumination can be added to the list of pressures on our moth fauna and consequently on pollination services. 

At a time of growing concern about global warming, light pollution may sound like a secondary problem. But the more scientists look into it, the more they learn that this is a serious environmental threat. And while sorting out the climatic mess will be tricky and complex, the light pollution problem is relatively easy. The first, obvious and straightforward measure is to turn off unnecessary lights. When illumination is needed, it could be dimmed, shielded or limited to specific areas such as pavements or roads.

Light designs and their impact on nearby biodiversity © AlexCairns, Wikipedia Creative Commons

Light dimming is good for the environment and for the economy too. When in 2018 the city of Tucson, USA, converted nearly 20,000 of their street lights to dimmable LED lights, the city saved £1.4m from its annual energy bill.

Preserving and protecting the night time environment is an important but neglected aspect of conservation. A darker world would benefit moths and other species, and it would be good for us as well. We could sleep better or go stargazing again. 

European artificial sky brightness on an increasing scale (black, blue, yellow, red) © Falchi et al. 2016. Science Advances 2(6) e1600377

Phoenix rising from the sand

By Athayde Tonhasca

As the waters subside in Germany and the country recovers from July’s catastrophic floods, naturalists may soon be able to evaluate the damage to one species caught in the deluge: the grey-backed mining bee (Andrena vaga). This bee is at home on river flood plains, grasslands, meadows, coastal areas, anywhere with alluvial soils – soil derived from sand and earth deposited by running water – and plenty of willows (Salix spp.) nearby.

A grey-backed mining bee © Ocrdu, Wikipedia Creative Commons

Female grey-backed mining bees dig their nests on spots of firm, sandy soil with sparse vegetation. The species is solitary, although females tend to nest close to each other in aggregations that can be thousands strong. Willows are their only source of pollen, but nectar is taken from a variety of flowers.

A grey-backed mining bee nesting aggregation © Mohra et al. 2004. Solitary Bees: conservation, rearing and management for pollination

Calamitous floods aside, to build a home on flood plains seems like a disaster waiting to happen. Water levels rise and fall, waterways change courses, river banks are washed away: riparian habitats are fragile and ephemeral. But none of this is the end of the world for grey-backed mining bees. Although floods may destroy large numbers of nests or even wipe out whole populations, these bees are well-adapted to disperse and colonise new places. In fact, fragmented populations dispersed over large areas are genetically similar, which suggests free and frequent interconnections between them.

Seven grey-backed mining bee nesting aggregations (red dots) in Germany © Mohra et al. 2004. Solitary Bees: conservation, rearing and management for pollination

Moreover, finding a new neighbourhood has a health benefit. Local populations of grey-backed mining bees grow steadily over the years, with more and more females sharing a nice nesting spot. These agglomerations do not go unnoticed by predators and parasites such as the nomad bee Nomada lathburiana. This parasite invades mining bee nests and lays an egg in the host’s brood cell; the invader’s larva emerges, kills the host’s egg or larva, then eats its provisions. A grey-backed mining bee aggregation targeted by parasites may contract by 50% in four years. But these population crashes are not all caused by natural enemies; some females just up sticks to build new nests on parasite-free sites.

The parasitic bee Nomada lathburiana © James K. Lindsey, Wikipedia Creative Commons

The grey-backed mining bee has been recorded intermittently in Britain since the 1930s, although its identification has not been confirmed until 2014. Currently this bee is confined to a few colonies is southern Britain: its populations may expand or be eliminated if nest aggregations are to be hard hit by rising waters. But even in this doomsday scenario, the grey-backed mining bee is not likely to be gone for long: wandering females in continental Europe should have no problem in crossing the English Channel and making themselves at home in Britain. This ‘here today, gone tomorrow’ lifestyle helps explain the difficulty in tracking the grey-backed mining bee and assessing its conservation status: it was labelled ‘endangered’ in 1987, ‘believed extinct’ in 1991, and ‘data deficient’ in 2020. As a species fine-tuned to transitory and unstable habitats, and highly adept at dispersing and colonising new territories, this unassuming bee takes natural disasters in stride; they are just facts of life.    

Spooked hikers and choughs chuffed to bits

By Athayde Tonhasca

During these unprecedented/strange/challenging times (pick your favourite cliche), many Britons have swapped their holidays abroad for the domestic great outdoors. This shift may help explain a spike in the number of bee swarm sightings along trails and in open spaces. In most cases, people are witnessing the comings and goings of the heather colletes (Colletes succinctus). This bee is usually found on heathlands, drier parts of moorland and coastal dunes – places with abundant heather (Calluna spp.) and heath (Erica spp.), its main sources of pollen.

A heather colletes © gailhampshire, Wikipedia Creative Commons

The heather colletes nests underground in bare or thinly-vegetated south-facing spots; sandy banks quickly warmed by the sun are particularly favoured. Each female digs a burrow, stocks it with pollen and lays an egg on the pollen mass. The larva feeds on the pollen and emerges as an adult the following year. 

Like many solitary bees, heather colletes nest close to each other, usually cheek by jowl. These aggregations can be massive: in one case, 60 to 80,000 tightly packed nests along a 100-m stretch of a river bank. Not surprisingly, these concentrations of swarming bees have prompted many a rambler to turn back or give a wide berth to the restless mob of honey bee lookalikes. Such precautions are unnecessary because these bees are harmless. They are not at all aggressive, and their stings are too weak to penetrate human skin. People who stop to admire them may catch a sight of clusters of bees rolling around. These are mating balls, comprising several males jostling furiously to mate with a female, who is hidden in the middle of the melee. As soon as a male succeeds – usually the larger one – the mating ball breaks apart. Females are monandrous, that is, they have one mate at a time, so they are not receptive to other males. 

Nest aggregations, which are common among several species of mining bees, are a bit puzzling because of the risks they represent. The abundance of provisions (pollen and nectar) stored by female bees, and so many juicy larvae and pupae in the same place are godsends to predators and parasites. 

So why do bees aggregate? It could be that adequate nesting sites are scarce: the ground has to be within certain physical specifications for secure tunnelling – the right type of soil, texture, drainage, slope and temperature – so several local bees may be attracted to the few good spots. Nesting needs help explain why many solitary bees display natal philopatry, which is the tendency to return to the site of their birth. It makes sense for a newly emerged bee to stick around: why take chances somewhere else when its place of birth ticks all the boxes? So the colony keeps growing, sometimes for decades. Aggregation may also result from having food nearby: broods have better chances of success if their mothers had easy access to pollen and nectar.

Whatever the reason, aggregations are quite handy for farmers who take advantage of the crop pollinating skills of some species such as the alkali bee (Nomia melanderi).

Alkali bee nests at the edge of an alfalfa field in America © Jim Cane, Agricultural Research Service, US Department of Agriculture

On the island of Colonsay, another species appreciates heather colletes nest aggregations: the red-billed chough (Pyrrhocorax pyrrhocorax). This bird feeds mostly on arthropods, and ants, beetles, moths and spiders are its usual prey. The choughs on Colonsay have learned to excavate heather colletes nests to get a nutritious, plentiful meal. 

A red-billed chough, a heather colletes predator © gailhampshire, Wikipedia Creative Commons

Hungry choughs are not likely to threaten heather colletes populations, considering the small number of birds on the island and their preference for farmland food such as crane flies and dung beetles; bee meals are probably opportunistic.

The heather colletes has experienced a small decline throughout Britain in the last 10 years or so for unknown reasons, but the population is still widespread and abundant in many places. They will probably carry on amazing and sometimes unintentionally startling nature ramblers for years to come.

The name sounds right

When it comes to species, scientific names are used all over the world.  This is with good reason, as their ever-lasting benefit is avoiding confusion and the difficulties of translation. However, there is a place for local names, and Scotland has a particularly rich range of them. Bumblebees are well served in this regard.

Depending on which part of Scotland you are in, the chances are you will find an affectionate name for bumblebees in general. These range from ‘bummer’ to ‘bummiebee, with the likes of ‘bumbard’, ‘bummie’ and ‘bumbee’ featuring too.  The ‘bum’ element of the name refers to the distinctive noise bumblebees are famed for. That’s not surprising. Indeed the scientific name Bombus (which covers bumblebees) derives from the Latin Bombus: to boom, buzz or hum.

That takes us on neatly to ‘droner’, another descriptive name which finds its origins in the sound bumblebees make.

When you drill down into individual species, then the names become even more charming.  Visual appearances as well as sounds begin to feature. A good example is the old ‘baker-bee’ or ‘dusty miller’ moniker given to the common carder bee, which reveals the observation that the flower-spattered, dusty looking, brown coats which bakers used to wear visually echoed a common carder dusted in pollen.

The north-east of Scotland is home to Doric, the regional name for the Scots language as spoken in that part of the world. And it gives us the delightful fusion of sound and vision that is ‘Foggie-toddler’. The roots of the name reflect that fog, an old Scots word for moss, and toddling, which depicts a gentle moving about with the occasional soft accompanying sound.  The ‘foggie-toddler’ name was adapted further in some districts and hence names such as ‘foggie-bee’, ‘foggie-bummer’ and ‘toddler-tyke’.

In Gaelic you will come across Seillean-mòr, pronounced as ‘shellen mor’.  The two elements of the Gaelic name give us Seillean (“bee”) and mòr (“big”). It’s a lovely concise reference.

Scotland, of course, isn’t unique in having local names for bumblebees. Delve into older use of English and you will come across humblebee instead of bumblebee. 

The Humble-bee, by Frederick William Lambert Sladen, was perhaps the great breakthrough bumblebee book. Written in 1912, and recently reprinted, Sladen’s masterpiece is perhaps the last significant use of the ‘humble-bee’ reference. Again it was the distinctive ‘humming’ sound of the moving bumblebee which inspired the name.

Perhaps ‘humble bee’ usage was already on the way out as Sladen made his literary mark.  Two years before Sladen’s book busied printing presses, Beatrix Potter’s Mrs Tittlemouse included a snippet in which the mouse was rather taken by the sound and energy of ‘lodgers’ (bees) when pulling out moss in her mouse hole. Potter conveyed this through using the word ‘bumble’ in the character ‘Babbitty bumble’.

Let’s end this whimsical whistle-stop tour by returning to the scientific name. Bombus is predictably accurate and hones in on the much loved noise that bumblebees make. However, it’s a name that just like the many local versions fits extremely well.

Find out more about scientific names, and their Latin roots, in the blog What’s in a name

Stylopized, emasculated and zombified: the risks of visiting a flower

By Athayde Tonhasca

‘Bizarre’ and ‘weird’ are overused adjectives for describing many characters and events of the natural world. Life is way too complex and varied to conform to familiar patterns, so the out-of-the ordinary is all around us, even though we not always see it. But when the discussion turns to stylopids, it’s difficult to avoid talking about the bizarre and the weird.

Stylopids (or stylops) are small, seldom seen and poorly known insects with about 700 described species, 10 to 16 of them in Britain; the true figures are likely to be much higher. They are parasites of other insects such as bees, wasps, plant hoppers and leaf hoppers. From a distance, male stylopids can be mistaken for flies, but their ruffled wings give them away and explain the name of this group of insects: the order Strepsiptera, from the Greek strephein (to twist) and pteron (wing). Twisted-wing insects is another common name for them. 

Males have branched antennae, and their eyes are berry-like structures comprising dozens of image-forming eyelets. This unusual array inspired the development of new cameras of reduced size and sharp images, which are handy for smartphones. Males cannot feed because their mouthparts are not developed. But never mind going hungry; they don’t live for more than a few hours. Their only objective in life is to use their fancy eyes to find a female and mate.

A male stylopid © Mike Quinn, TexasEnto.net, Mckenna & Farrell, 2010, PLoS ONE 5(7):e11887; and detail of a male head © CSIRO, Australian Insect Families

Females look nothing like the males. In fact, they don’t look like your ordinary insect at all because they don’t have wings, antennae, legs, mouthparts or eyes: they are neotenic, i.e., they retain their larval features. An adult female does not need a fully-formed body since she never leaves her host: she will develop and die semi-buried in another insect. ‘Semi-buried’ because the tip of her cephalothorax (the head and the thorax fused together) protrudes from the host’s abdomen. 

A bee carrying a female stylopid. Scale bars = 1 mm © Soon, V. et al. 2012. Entomologica Fennica 22: 213-218.

Through this exposed area, the female releases a pheromone to attract males. Once suitors finds her, they face an anatomical challenge. Only parts of her head/thorax are exposed, which doesn’t bode well for conventional insect romance. But this setback is nothing compared to the facts that she doesn’t have genitalia, and her eggs float in the haemolymph (‘blood’). So a male has only one course of action: the disturbingly sounding traumatic or hypodermic insemination. He pierces the female’s cuticle with his penis and injects his sperm into her haemolymph.

Two male stylopids going after a female tucked in a bee © W. Rutkies at Peinert et al. 2016. Scientific Reports 6: 25052

The deed done, males soon die. The fertilised eggs hatch inside the female, giving birth to thousands of tiny six-legged, very active and agile larvae called planidia (just like blister or oil beetles). The planidia feed on mum’s innards and eventually crawl out of her body to disperse and start looking for a host of their own. 

A stylopid planidium, and planidia emerging from a female stylopid. Scale bars = 0.1 mm © Kathirithamby, J. 2018. Biodiversity of Strepsiptera

A wandering planidium climbs a flower to wait for an unsuspecting visitor. When a bee or wasp lands, the planidium somehow hitchhikes a ride to their nest. We are not sure how it does this: it could hide in the pollen, or possibly be swallowed with the nectar sucked up by the flower visitor, then released when the host regurgitates nectar inside the nest. Chances are it will end up in the wrong nest, so most planidia are done for. But the staggering fecundity of female stylopids compensates bad odds: they can dish out 750,000 planidia, so a few are likely to find a suitable host.

Once inside the right nest, the planidium burrows into a host’s egg or larva and transforms into a traditional legless, grub-like larva. It is followed by other larval stages, pupation, and finally adulthood – by then the host has also become an adult. If it’s a male stylopid, it squeezes out of the host and flies away, usually leaving a big gap behind and killing the host. If it’s a female, it will park itself in the host’s abdomen. 

A male stylopid emerging from a wasp © Kathirithamby, J. 2009. Annual Review of Entomology 54: 227–49

The story above is a peep at stylopids’ life histories, as there is considerable variation depending on the species and type of host. And if all this sounds outlandish, there is more to come.

Stylopization (parasitism by stylopids) causes all sorts of physical and behavioural eccentricities in the host, all for the parasite’s benefit. Such as infertility. Reproduction involves mating, nest building, nest provision, etc., which are risky and energy-consuming, therefore not beneficial for a parasite. Stylopids solve this problem by disabling the host’s reproductive organs, functionally castrating them. Some stylopized bees have reduced scopae (pollen-carrying structures) and seldom if ever carry pollen: there’s no point, as they don’t have a brood to provide for. Contrary to what happens to most parasitized insects, stylopization often lengthens hosts development; they live longer so that stylopids have more time to mature. Some stylopized bees are led to stand still on a grass or flower stems with their head downwards. Such a zombie state greatly facilitates stylopids’ mating business. 

In Britain, furrow bees (genera Halictus and Lasioglossum), yellow-face bees (genus Hylaeus) and especially mining bees (genus Andrena) are victims of stylopids, but we have little information about their interactions and no idea about consequences of parasitism. 

Stylopids are odd and enigmatic, but they are also one of the most complex and intriguing groups of animals. They are evolutionary marvels that have puzzled and awed generations of entomologists and naturalists, and more surprises should be revealed from future research. It seems quite fitting then for the august Royal Entomological Society to have adopted a stylopid (Stylops kirbii) as a representative of the organisation.

Royal Entomological Society badge © Wikipedia Creative Commons

Islay’s ideal idea

Every once in a while you come across a project that stands out for its clarity and impact.  I had this experience recently when holidaying in Islay.  The project in question aims to make most of this beautiful island’s roadside verges a rich habitat for pollinators. 

Inspired by the work of Plantlife, who had been advocating the value of verges for pollinators, the team behind the Islay Natural History Trust set to work.  Linking up with supportive staff at Argyll & Bute Council, a plan was hatched to trial a change in verge cutting practices.

The idea was simple yet effective.  To leave verges to flower, and only cutting late in the season after the plants have set seed and finished flowering. It’s a strategy that is gathering momentum across local authorities and is a welcome development for our hard-pressed pollinating insects.

The Islay Natural History Trust teamed up with The Botanist Foundation and embarked on a two-year study of some of the less travelled routes on the Rhinns area of the island. Around 100 km of roadside verges were surveyed in 2017 and 2018. This allowed the Trust to assess the plant species they had and how pollinators were making use of them. They then persuaded the Council to adopt a new approach to verge management. 

If successful, the initiative will create a range of benefits – the floral diversity will be improved, pollinators will have more food, grass will no longer dominate verges, and there will be savings in verge management.

The group is mindful of the details as well as ‘the big picture’, and particularly protective of verges that provide space for orchids around Port Wemyss and Portnahaven, for example. By relaxing mowing regimes, these orchids will flower, with discretionary and flexible verge cutting by volunteers to ensure road safety.

Portnahaven

Of course verges can vary, even across a single island. That’s why one area is subject to a trial seeding of Yellow Rattle to tackle grasses which largely created a major need for cutting in the first place and would ultimately subdue other plants. Yellow Rattle is an annual plant typically found in ancient meadows. Its roots latching onto those of surrounding grasses and pulling nutrients from their roots. For those concerned that Yellow Rattle might ‘run amok’, the group have stressed that sowing is only within the one metre strip that the council currently cuts. This small sub-project was set out to seed up to 4 km of verges around the of Loch Gorm and Gruinart area. The group will be able to observe what impact the introduction of ‘the meadow maker’ has.

By supressing dominant grasses, the height of verge growth should be lessened and this in turn reduces the need for mid-season cutting. The fuel saving will be a step down the road to reducing the carbon footprint associated with verge management.

Some footpath verges have also been transformed into pollinator-friendly routes

And of course when the grasses are suppressed, other plants move in. Chief amongst them from a pollinator perspective are clovers, yarrow, oxeye daisy, lesser knapweed and meadow vetchling. 

There is also something to be said also for the ‘transport corridor’ approach, which is gaining traction in the central belt.  Basically florally rich verges can act as route for pollinators to move through landscapes, and in an island not short on swathes of sheep-grazed pasture and barley filled fields, the verges can offer a lifeline.

That’s a fittingly optimistic note to end on. The work in Islay is an inspiration and could be a model to help pollinators across the country. Indeed, as you might often say on Scotland’s whisky island … “Cheers!”

Find out more about the Islay survey in their publication – The Islay Pollinator Initiative

Islay, isle of stunning beaches and increasingly impressive verges

Pollination: a wealth and health trade

By Athayde Tonhasca

For centuries, berries of the açaí palm (Euterpe oleracea) have been a staple food for the people in the Amazon, thanks to the fruits’ high caloric content. In the 1990s, açaí (ah-sah-ee), served as frozen pulp or juice, became a fashionable street food in Brazilian cities, a craze boosted by bogus claims about ‘antioxidant’ and ‘superfood’ properties. In no time the purplish berry left its swampy Amazonian plains to conquer the world: today açaí na tigela (açaí on a bowl) is available in restaurants and health food joints across Europe, America and Japan. 

Açaí berries and a traditional bowl of açaí with fruit and granola © CostaPPPR (L) and Gervásio Baptista, Wikipedia Creative Commons

Açaí generates an estimated US$ 1 billion/yr for the Brazilian economy, and the market is growing at a brisk pace. Most berries are harvested from palms growing in the wild, and everyone enjoying their benefits – subsistence farmers, traders, exotic food buffs and the taxman – must be grateful to the insects that pollinate the palm’s inflorescences, mostly stingless bees.

Stingless bees Trigona pallens, big contributors to the Brazilian economy © Nemésio, A. et al. 2013. Brazilian Journal of Biology 73: 677-678

The açaí berry is just one of several pollination-dependent products exported from Brazil and many other countries. When all the data is put together, it is estimated that more than 50% of the world’s exported crop products depend on pollinators.

Log-transformed tons of exported pollination-dependent Brazilian crops, 2001–2015 © Silva et al., 2021. Science Advances 7, eabe6636

Deforestation, fires and habitat degradation – which includes the spread of crop monocultures – threaten this global pollination-based trade, with heftier consequences for developing countries.  We may shrug our collective shoulders at what seems to be other people’s problems, but we must remember that a significant portion of the vitamins and minerals essential for our diet comes from insect-pollinated food, and most of it is imported. Many types of apples, pears, avocados, citrus fruits (e.g., orange, tangerine, limes, grapefruit) cucurbits (such as melon, courgette, cucumber, squash), peas and beans benefit from or are greatly dependent on insect pollinators, although some varieties are self-fertile and need none. Most vegetables consumed in the UK don’t require pollination for yield, but many of them may need pollinators for seed production; these include brassicas (broccoli, Brussel sprouts, cauliflower, cabbage, kale, etc.), carrot, fennel and parsley.

Pollination is important for our nutritional needs, and also for a few of our pleasures and indulgences. We may carry on through life without a bowl of açaí, but much less happily in the absence of coffee or cacao (hence chocolate), both of which need pollinators for adequate yield and high crop quality. House parties are more satisfying when stocked with bowls of almonds, Brazil nuts and cashews, none of which would be available without insect pollinators. If it wasn’t for bees, Worcestershire sauce wouldn’t be on the dinner table, at least not in its existing version. The condiment contains tamarind extract, and the tamarind tree needs bees for pollination. The list of examples can be quite long.

No nuts or Worcestershire sauce without pollinators © Melchoir (L) and Bardbom, Wikipedia Creative Commons

Brexit and the Covid pandemic have sharpened our attention to food security, so perhaps pollination, which is important to our diet, health, wellbeing and economy, will get a brighter spotlight. But just like climate change, threats to this ecological service are not confined by borders. Deforestation, pollution, wildfires and biodiversity losses may hurt far-flung places first, but their effects will cascade down to us. More than ever, we need to ‘think globally, act globally’.

Fabulous Forvie

Most visitors to Forvie National Nature Reserve, it’s fair to say, go in expectation of glimpsing a range of birds and enjoying the fringe of sand dunes.  But of late there has been increasing appreciation of the number of pollinators, and given the rich floral diversity perhaps that shouldn’t be too much of a surprise.

Our colleagues at Forvie manage a rather impressive meadow specifically for pollinators. The wildflowers here benefit from a cutting regime that emphasises the value of a late cut and the removing of cuttings. This allows longer flowering periods and seed setting. By removing the cuttings, the team at Forvie ensure that bigger, tougher, ranker plant species don’t take over.

The meadow was increasingly drawing admirers, and the team set up a short trail next to the visitor centre.  Information boards explaining species, habitats and behaviours proved extremely popular; visitors would stroll round taking their time to absorb the information and pausing studiously like Magnus Carlsen over his next chess move. The range of pollinator-friendly messaging also targets visiting gardeners and community groups with hints on how they could do their bit for nature in their own space.  

This smorgasbord for bumblebees, hoverflies, solitary bees and honey bees and others insects is seldom quiet. The butterflies that linger on the flower heads are one of the highlights.   It also offers a splash of colour for visitors to savour. All of this takes place within a few steps of the main car park, and a wildflower trail over the heath makes for a real bonus.

Forvie’s soil is thin, sandy and poor in nutrients, which is ideal for wildflowers .  However, given the harsh coastal climate, many plant species tend to be small and low-growing. 

So to the edited highlights.

Look out for bird’s-foot trefoil. A member of the pea family, the flowers resemble those of the sweet pea, and emit a similarly pleasant fragrance. On a hot day the smell can be almost intoxicating, helping to attract insects to pollinate the flowers. Bird’s-foot trefoil has several colloquial names depending on where you are in Britain. In southern England it’s known as ‘bacon and eggs’, due to the flowers’ colouration – orange-red for the bacon, and yellow for the eggs of course! But in north-east Scotland it’s also called ‘craa’s taes’ (literally ‘crow’s toes’). This name reflects the shape of the seed pods which for some resemble a crow’s foot.

Other draws include orchids, and the reserve boasts a few. Northern marsh, heath spotted, and the charmingly named frog orchid are worth searching for. If blue or purple are the colours for you, then you will enjoy Scottish bluebells, germander speedwell, viper’s bugloss, self-heal and wild thyme.  If you are lucky you might catch a glimpse of purple milk-vetch in June and July.  For those who prefer a white palate you will be in good company, as an array of bees favour the splashes of white clover. And who could ignore the yellows with dandelion, mouse-ear hawkweed, lady’s bedstraw (in past times it was used for stuffing mattresses), and tormentil vying for your attention.

But amidst this heady floral variety a word of warning for prospective visitors. There are few guarantees in nature, and meadows can differ markedly from year to year

One thing is for sure, it’s never the ‘same old, same old’ at Forvie.  Why not pop a reminder in your calendar for 2022: ‘Must visit Forvie’?

Visit Forvie National Nature Reserve

With sincere thanks to Mark Williamson at Forvie NNR for his images and help with this piece.

An enemy’s enemy is a friend

By Athayde Tonhasca

A creature named ‘bee wolf’, ‘bee killer’ or ‘bee hunter’ cannot bode well for a bee. Indeed, the solitary wasp Philanthus triangulum, the European bee wolf, can be a serious headache for the honey bee (Apis mellifera).

From early July to mid-September, a female bee wolf can often be found busy digging a long tunnel (up to a metre deep) on the ground, usually on a sunny, sandy bank. This main tunnel will branch into several shorter burrows, each to become a brood cell. When she’s finished with house building, it’s time to go hunting to provide for her brood. Solitary and cuckoo bees would do as prey, but honey bees are the main draw. The bee wolf snatches a honey bee and stings it. The honey bee may try to defend herself with her own sting, but she’s no match for the stronger enemy. Attacker and attacked fall to the ground, and the honey bee quickly becomes paralyzed by the wasp’s powerful neuromuscular venom. Sometimes the bee wolf seems to be doing a mouth-to-mouth resuscitation attempt on her victim, but in fact she is lapping up nectar collected by the honey bee. The bee wolf grabs her prey firmly and brings it back to her nest. Watch the whole drama.

A bee wolf returning home with a paralyzed honey bee © Stevelaycock21, Wikipedia Creative Commons

The bee wolf continues hunting, bringing enough booty to stock each brood chamber with up to six honey bees. When the nest is full, she lays one egg on a honey bee in each chamber and seals the tunnel entrance. The larvae hatch in 2-3 days and feed on the living but incapacitated honey bees. When a larva is finished eating, it spins a protective cocoon to hibernate through winter, and a new adult emerges in spring.

Bee wolves are solitary but tend to nest close to each other, possibly because good nesting sites are hard to find. And these wasps can make excellent use of good spots: in continental Europe, nest aggregations may be 15,000 strong. With each wasp capturing up to 100 bees over the season, local honey bees can be depleted quickly. 

Honey bees are widespread, and with 20 to 50 thousand residents per hive during summer, it would seem that bee wolves have it easy. Enter the cuckoo wasp Hedychrum rutilans.

Hedychrum rutilans © Pudding4brains, Wikipedia Creative Commons

This colourful, iridescent creature is one of the 3,000 or so species of chrysidid wasps (family Chrysididae). Chrysidids are parasitoids, that is, they lay their eggs on the host or inside its nest, and their larvae eat the host’s offspring. Unfortunately for the European and other bee wolf species, this cuckoo wasp targets them. 

Most chrysidids wait for the host’s nest to be sealed up to lay their eggs inside the brood cells. H. rutilans has different ideas. It often hangs around the host’s nest entrance, waiting for the bee wolf to leave on another hunting expedition. It then enters the nest and lays an egg on a paralyzed honey bee already there, waiting to be entombed. Or it may take a blitzkrieg approach, laying an egg on a honey bee as it is dragged by the bee wolf into her nest. If the cuckoo wasp is successful either way, the bee wolf is in trouble. The emerging cuckoo wasp larva kills and eats the bee wolf larva, and the honey bees as well.

The cuckoo wasp seems to avoid detection inside the bee wolf nest thanks to chemical mimicry, that is, by releasing the same substances that bee wolves use to recognize each other.  Chemical mimicry protects the cuckoo offspring too; if the bee wolf picks up the smell of an intruder inside a brood chamber, it throws away the stored honey bees. The cuckoo wasp is not so safe in the open: if spotted, it will be attacked by the bee wolf. But like most chrysidids, H. rutilans is thick-skinned and rolls up in a defensive position so that sensitive parts are protected from stings and bites. Watch a cuckoo wasp escaping an attack.

A female chrysidid in a defensive position © Chrysis.net

The European bee wolf was first recorded in southern Britain in the 1990s, and since then it has moved north (with no notable consequences for honey bees so far). This wasp responds well to warm summers, so its expansion is likely to extend into Scotland. Predictably and unavoidably, H. rutilans followed its host into Great Britain, although records are still scarce and confined to the south. Time will tell whether cuckoo wasp distribution will expand as well. In continental Europe, this parasitoid can wipe out local bee wolf populations, but nobody can predict how the honey bee/ bee wolf/cuckoo wasp triangle will shape up in Britain. Curious naturalists will follow the plot closely.

Does H. rutilans have its own parasitoids? We don’t know, but that’s possible. No species is free from parasites, predators or pathogens. So Jonathan Swift’s witticism about an infinite chain of fleas has some biological truth:

So, Nat’ralists observe, a Flea

Hath smaller Fleas that on him prey,

And these have smaller yet to bite ’em,

And so proceed ad infinitum:

Thus ev’ry Poet, in his Kind

Is bit by him that comes behind.

On Poetry: A Rhapsody (1733).

Pollination, a game of hide and seek

By Athayde Tonhasca

For bees, pollen is an indispensable source of protein for egg production and larval development. So if a bee had it her way, she would scoop up every pollen grain from a flower. And she’s good at it, storing pollen securely on specialised transport structures, usually on her legs or under her abdomen. She also grooms herself regularly to remove stray pollen grains stuck to her body. As a result of this meticulous work, some bees take about 99% of the powdery stuff back to their nests. The ‘wasted’ 1%, which accidentally drops off or is left clinging to the bees’ hairs, is all a plant has for pollination. 

A bee covered in pollen grains: most of them will be scooped up by the bee © Ragesoss, Wikipedia Creative Commons

Bees’ efficiency puts plants in a jam. They need flower visitors to transport pollen and for sexual reproduction, but the greedy blighters want it all for themselves. Pollen is metabolically expensive, so a plant can’t afford to produce lots of it and then lose most to palynivores (pollen eaters). But if it produces too little, bees may not be interested in dropping by.

To deal with this dilemma, plants have evolved several strategies to keep visitors coming and at the same time minimizing pollen loss. Some species hide pollen inside their anthers (poricidal anthers), others produce indigestible or even toxic pollen so that only a few efficient, specialised pollinators can get to it; the palynivore hoi polloi is kept at bay. Another clever approach is to induce bees to be less efficient at grooming, so that more pollen grains are available for deposition on a receptive flower. And one way to accomplish this is through nototribic flowers. This term applies to flowers built in such way that their stamens and style come in contact with the dorsal surface of the bee’s body. They are common in the group of sage, mint and rosemary plants (family Lamiaceae) and figworts (family Scrophulariaceae). 

A honey bee on a meadow clary (Salvia pratensis) flower cut open laterally, and a schematic drawing showing the stamen touching the bee’s back © Reith, M. et al. 2007. Annals of botany 100: 393-400

Bees use their front legs to wipe their heads and antenna, and their middle and hind legs to clean their thoraxes and abdomens (you may have watched a bee grooming itself). But the space between their wings is a blind spot – think about an itch right between your shoulder blades, and you will understand the bee’s problem. The pollen grains deposited in this unreachable area are then taken to another flower.  

Pollen of meadow clary on the back of Bombus terrestris under UV light
© Koch, L. et al.  2017. PLOS ONE 12(9): e0182522

Some flowers hide pollen at the bottom of their corollas, and bees such as the fork-tailed flower bee (Anthophora furcata) must creep into these narrow, tubular structures that don’t allow much moving about. The bee vibrates her flight muscles to release the pollen, which gets attached to her head. She pulls out of the flower and scoops up the pollen with her front legs, but not all of it; some grains are stuck to thick, curved hairs between the antennae; these grains can’t be groomed, so become possible pollination agents.

A fork-tailed flower bee has to use her head – literally – to pollinate © Nederlands Soortenregister, Wikipedia Creative Commons
Facial hairs of a fork-tailed flower bee © Muller, A. 1996. Biological Journal of the Linnean Society 57:  235-252

A few plants resort to making life difficult for bees whose habits are not the best for their interests.  And these could be corbiculate bees, that is, bees that carry pollen in their pollen baskets (corbiculae) such as honey bees and bumble bees. Corbiculate bees use regurgitated nectar to stick the pollen together so it can be bundled up nicely for transport. Few pollen grains detach from a corbicula, and the moisture quickly reduces their viability. Most plants live with that, but some would rather save their pollen for bees that transport it on their scopae, which are elongated setae (‘hairs’) on their legs or under the abdomen. These non-corbiculate bees are not as tidy as their corbiculate counterparts: they do not wet and compress the pollen, which is taken away just like dust particles clinging to the hairs of a brush or a broom (scopa, in Latin).

Pollen tightly packed on a bumble bee’s pollen basket (corbicula) (L) and loosely attached to the scopa (fringe of hairs in the abdomen) of a megachilid, a solitary bee © Tony Wills (L) and Vijay Cavale, Wikipedia Creative Commons

To discourage corbiculate bees from making off with their pollen, plants such as the common hollyhock (Alcea rosea) and other mallows (family Malvaceae) produce pollen covered with spines. These echinate (prickly; covered with spines or bristles) pollen grains are relatively large, difficult to handle and to mould into neat pellets. Echinate pollen is a headache for corbiculate bees, the efficient packers, but not a problem for messy pollen harvesters such as solitary bees. As a result, more pollen grains are dropped off from bees, increasing the chances of pollination. 

Echinate pollen grains from three Malvaceae species © Konzmann et al. 2019. Scientific Reports 9: 4705

All these adaptations illustrate the wonderful complexities of an evolutionary give and take: insect pollination is a negotiation between parties with conflicting interests. Plants can’t give away too much pollen but can’t risk being overly stingy: bees would take all the pollen they could handle, but settle for what’s available as long it’s worth their time and energy. Every plant-pollinator combination is an example of a mutually beneficial compromise. It’s natural selection as its best.