Wave upon wave of colour

By Therese Alampo with images from Pauline Smith

The conditions at St Cyrus NNR make it an absolute haven for a diverse range of pollinators, and spring, summer and autumn are a fascinating time for anyone who wants to delve into the buzz and hum of this world.

The climate at St Cyrus NNR, low rainfall, the shelter from the cliffs and dunes create a unique microclimate which supports a breath-taking variety of flowering plants some found at their Northernmost limit or very uncharacteristic of the area.  These plants do a season round Mexican wave of colour and scent offering up a veritable smorgasbord of pollen and nectar to the invertebrates on the reserve.

Early in the season the pussy willow offer pollen for the big fat queen bumblebees to delve into, turning them into buzzing yellow powder puffs!  They have been in torpor all winter and emerge hungry and needing to find food and a nest site for their developing eggs and brood.

Then the hoverflies start arriving, across the sea from Continental Europe to join in the buzz, the mining, mason and leafcutter bees join in the party soon after.  

Then to the lepidoptera. We have over 500 species, many of which are important pollinators, the moths are my favourite and with names like Merville de jour, gold spangle and Hebrew character who could resist the intrigue.

These species are key to our survival on this planet, how lucky are we to see a slice of the planet so rich in pickings and them enjoying every bit of it.

When you step foot on the main path into the reserve you are confronted with a scruffy haven, just stopping and looking at the umbel (flower head) of cow parsley or sweet scicily on the way past offers up a comedic clutter of hover flies, soldier beetles, bumblebees and others all head down and bottoms up.

Even offering a little information about a few key pollinator species in the form of a simple pollinator trail helps to connect people to the importance of pollinators, and can spark so much interest!  Everyday we see people stopping to read the information on the short trail, capturing an audience that may just be on the way to the beach.  I love people’s reactions to the trail and the fascination, particularly to the wasp panel, “really, wasps are useful I never knew that”!

It’s complicated

By Athayde Tonhasca

Himalayan balsam (Impatiens glandulifera) was brought to the British Isles in 1839 as an addition to Kew Gardens’ collection of ornamental plants. As usually happens with introduced species, Himalayan balsam escaped into the wild, causing consternation ever since. It has spread throughout damp woodlands and along rivers, flourishing in thick stands up to 2 metres high that overshadow the local vegetation. This plant does well in a variety of climatic conditions and soil types, and has a tremendous capacity to spread.

So nobody likes Himalayan balsam. Nobody but pollinators.

Himalayan balsam © MurielBendel, Wikipedia Creative Commons
Himalayan balsam © MurielBendel, Wikipedia Creative Commons

This invasive is a nectar factory. Each flower produces about 0.5 mg of sugar per hour, a rate far higher than any European plant; flowers of most species yield less than 0.1 mg/h. And because the plant flowers late in the season, nectar it available at a time when other sources start to become scarce. So naturally, bumble bees, honey bees and wasps go for it with gusto. And there is something in store for hoverflies as well; they feed on the copious amounts of pollen produced by these flowers. Predictably, the number of bumble bees and other insects increase in areas invaded by Himalayan balsam. 

This abundance of food could have undesirable side effects. Many bees get the proteins, carbohydrates, lipids and amino acids they need from a variety of pollen sources. But thanks to the plentiful and readily available pollen from Himalayan balsam, bees stick to this easy option: in some situations, up to 90% of the pollen collected by honey bees comes from this plant, with unknown consequences to bees’ development and health. The profusion of pollen and nectar could also indirectly harm other plants: if native species receive fewer visitors, their pollination could be compromised. But the evidence for such outcomes is contradictory. Some studies suggest that Himalayan balsam reduces flower visitation and seed production of native plants; others have demonstrated no differences, or a ‘magnet effect’: Himalayan balsam attracted pollinators to itself and to plants nearby. 

A marmalade hoverfly (Episyrphus balteatus) and a common carder bee (Bombus pascuorum), two Himalayan balsam beneficiaries © Charles James Sharp (L) and André Karwath, Wikipedia Creative Commons
A marmalade hoverfly (Episyrphus balteatus) and a common carder bee (Bombus pascuorum), two Himalayan balsam beneficiaries © Charles James Sharp (L) and André Karwath, Wikipedia Creative Commons

Alien species are a hot and controversial topic among conservationists. Some highlight the damage caused by introduced species to the native fauna and flora, habitats, the economy and even human health. But other conservationists point out that alien species may have neutral or positive impacts: that is, they are alien but not necessarily invasive. The invasiveness of Himalayan balsam has been well documented, but there are mitigating factors in its favour: in some situations, this plant had no effect on local species composition, or at worst it only replaced a few ruderal species (plants that colonise areas that have been disturbed). And its presence may check the spread of harmful alternatives such as the giant hogweed (Heracleum mantegazzianum).

Assessing the impact of alien species is important because a great deal of money and resources have been spent on controlling or eradicating them, quite often unsuccessfully. It is usually assumed that invasive plants are bad for pollinators, but there isn’t much evidence to support this assumption. Like many aspects of species’ ecology, data are scarce, results are often contradictory, and generalisations are risky. In summary: it’s complicated.

The drinks are on me

By Athayde Tonhasca

The broad-leaved helleborine (Epipactis helleborine) is found throughout UK and much of Europe and Asia in all sorts of habitats, including urban and disturbed areas. This orchid was introduced to America, where it is viewed as an invasive species in some places. Despite its common occurrence and being the source of a reasonable supply of nectar, the broad-leaved helleborine is often ignored by insects, a fact noted by Charles Darwin.

The orchid’s small, inconspicuous, greenish/purplish flowers are not exactly good marketing for attracting bees and other pollinators. But one group of insects are keen visitors: wasps, in particular the European (Vespula germanica) and the common wasp (V. vulgaris). 

A broad-leaved helleborine flower © Björn S., Wikipedia Creative Commons
A broad-leaved helleborine flower © Björn S., Wikipedia Creative Commons

Adult wasps feed mostly on carbohydrates, which they get from nectar – or from your sugary drink, if you give them a chance. But the nectar of broad-leaved helleborines is special: it’s laced with chemical compounds, some of them with narcotic properties. It also contains ethanol and other alcohols, possibly as the result of fermentation by yeasts and bacteria. This chemical cocktail is toxic or repellent to many visitors, but not to wasps: they lap it up. Unavoidably, a concoction of opioid and morphine derivatives plus alcohol, even in minute amounts, has consequences for its consumers. Wasps become intoxicated and sluggish after a few sips, which suits the orchid very well. They spend more time on the flower, staggering about and thus increasing their chances of ending up with a pollinium (a sticky mass of pollen grains) glued to their heads. Watch it. Nobody knows if wasps are hungover afterwards.

A wasp with pollinia attached to its face © Saarland, Wikipedia Creative Commons
A wasp with pollinia attached to its face © Saarland, Wikipedia Creative Commons

This orchid has another trick up its sleeve besides inebriating nectar; it also lures wasps with false promises of prey for their larvae. It turns out that these flowers release chemicals that mimic green-leaf volatiles, which are produced by plant tissues when they are damaged by herbivores. Wasps are attracted to green-leaf volatiles in the hope of finding some juicy caterpillars chomping on the host plant. When a wasp gets to the flower, its attention is diverted to the sugary nectar, so the scent scam is forgotten.

Orchids are highly diverse: with approximately 25,000 described species, they make up about 10% of all flowering plants. About one third of orchids do not offer food rewards – nectar or pollen – to visiting pollinators. Instead, they have evolved all sorts of tricks to attract insects. Some flowers have the shape, colours or scents of food-rewarding plants; they may bait male insects by resembling female counterparts, or by releasing pheromone mimics; sometimes they charm visitors that are seeking a place to lay their eggs. Or by using a combination of artifices, as it is the case of the broad-leaved helleborine.

These deceiving orchids attract only a handful of insects that respond to specific chemical or visual cues, so many potential pollinators are excluded. But the strategy pays. Pollen is transported more efficiently for deceptive species than for those with multiple pollinators. This means that more pollen is taken to another flower of the same species, and less is dropped or deposited on the wrong flower.

Deception works for orchids, but how about their cheated visitors? Sometimes they are rewarded, but often they get nothing. We don’t have much information about the insects’ side of this relationship. They must benefit somehow, or at the very least they are not significantly harmed. This matters to wasps, as they pollinate around 5 % of all known orchid species.

Orchids provoke much fascination for their biology, diversity and exoticism. This level of attention has helped us appreciate better the role of wasps. Most of them don’t collect pollen, and their lack of body hairs – compared to bees – does not allow for many pollen grains to attach to their bodies. But if we go by their contribution to orchids’ reproduction, these important but often maligned insects have much to reveal about their part in pollination services.

An European wasp, a frequently cheated pollinator © User:Fir0002, Wikipedia Creative Commons
An European wasp, a frequently cheated pollinator © User:Fir0002, Wikipedia Creative Commons

Growing gains

Grow 73, a charity based in Rutherglen, works to encourage local growing, increase biodiversity, and improve the local environment. The hub of their efforts is the impressive community garden at Overtoun Park, but an ambitious project to create a green pollinator pathway from Rutherglen train station through to Cathkin Braes shows they have bigger plans yet. 

The group, who featured recently on BBC’s Countryfile programme,  are named after their G73 postcode in Rutherglen, which lies just a few miles south-east of Glasgow’s busy city centre. Established in 2015 by Eugine Aroutcheff, who came to Scotland from France around 28 years ago, and Lynn Semple the group started with the modest aim of looking for a place to grow fruit and vegetables.

They picked a good time to pursue that goal. In 2015 the Scottish Parliament had passed a Community Empowerment Act enabling communities to take over plots of dis-used land. Grow 73 used the Act to get a 15-year lease for three dis-used bowling greens in the park in addition to five areas they were already working on.

It is fair to say that Grow 73 have seized the opportunities that expansion has offered with some style.  Their plans now include a pond, more raised beds, community hub, poly tunnels and converting a small woodland into a natural play area. One of the greens will be kept as a wildlife area.

If their initial focus was a desire to grow food, it is fair to say that they are now making great strides in providing for biodiversity and in particular pollinators. Helped by the enthusiastic Rutherglen residents (who shifted 9 tonnes of compost when the project got underway) they are moving on from conventional growing plots, to providing a series of planters as ‘stepping stones’ for pollinators linking Rutherglen to Cathkin.

This will be achieved through their Rutherglen Network, which joins an array of containers and gardens into a ‘super highway’ for bees, or if you prefer a Bee-Line. Given that habitat loss and fragmentation are key challenges which our pollinators face this is a welcome approach. 

Each container has a selection of nectar-rich plants that are potentially a wonderful boost for pollinators. The group have deliberately left empty spaces in between the plants, so that the community can add their own plants to the planters. And there was help on hand to ensure that local planting was possible.

Eugenie, and her army of volunteers, put together kits of compost, potato seeds, flower seeds and reused coffee sacks during the pandemic, then delivered them to local homes in a stunning display of determination. The aim was to involve the people of Rutherglen in making these containers great for pollinators and a source of local pride. Wherever possible Grow 73 have worked with local groups and nurseries to ensure local buy-in to all that they do. Working in partnership has been a key principle for the charity.

And how they succeeded. By the time lockdown ended they could reflect on having delivered a staggering 10 tonnes of 650 individual growing kits to eager residents.   Now take a walk through Rutherglen and Burnside and you will see a range of pollinator friendly flowers popping up domestic gardens, containers, and even creatively planted old whisky barrels.  

Creating a green oasis required a strong belief and clear vision. The burgh of Rutherglen is steeped in political and industrial history, but since the final demise of industries as diverse as textiles, coalmining and chemical production the burgh has endured a legacy of post-industrial decline. Overtoun Park is in fact named after industrialist Lord Overtoun, who gifted the land on which the park was laid out in 1907. Although Lord Overtoun’s reputation was tainted by the discovery over the past 30 years of extensive local chromium dumping.

During the coronavirus crises, which forced people to stay local, there was a surge in interest in neighbourhood greenspaces. The charity in helping people of all ages and abilities to grow their own produce has fostered an appreciation of enjoying the outdoors, promoted leading more sustainable lives, and supported local biodiversity. What’s more, through these shared gardening activities and environmental improvements Grow 73 contributed significantly to improving the health and well-being of the local community whilst making Rutherglen a greener place. So much so that the aim is to improve biological recording by logging the insects (especially pollinators) and wildflower in the area.

Grow 73 have achieved a huge amount in a short space of time, but they won’t rest on their laurels. You get the sense that their ambitious plans are just the beginning of a story that could run for some time, and that’s great news for our vital pollinating insects and local residents.

Find out more:

Grow 73 Website 

Facebook =  www.facebook.com/Grow73/ 

Twitter =   //twitter.com/grow73 

On the Keep Scotland Beautiful website  

A plastic new world

By Athayde Tonhasca

Mr McGuire: I want to say one word to you. Just one word.

Benjamin: Yes, sir.

Mr McGuire: Are you listening?

Benjamin: Yes, I am.

Mr McGuire: Plastics.

Film buffs will recognise one the most quoted dialogues in motion picture history, where Mr McGuire advises young Benjamin Braddock on his career options in the 1967 classic ‘The Graduate’.

Mr McGuire was prescient: the plastics industry has expanded to levels unimaginable in 1967. Cheap, versatile, resistant and durable, plastic products are essential in today’s society. They are everywhere. So, unsurprisingly, they are an ever growing environmental problem: land, waterways and the oceans are stuffed with discarded plastic. 

Plastic rubbish is a blight on the landscape, but some birds and mammals have taken advantage of this abundance of material. Squirrels and opossums have learned to use straws, string and plastic bags for nest building; plastic fragments were present in about 14% of surveyed nests of the brown booby (Sula leucogaster), a seabird found around the world. So, diligent nest builders such as leaf-cutter bees were bound to join this team of opportunists.

Most leaf-cutter bees (genus Megachile) cut pieces of leaves or petals to build their nests; some use mud, pebbles or resin as construction materials. These bees usually nest in sheltered natural cavities such as burrows, crevices and hollow twigs. They are important pollinators, and a few species have been reared commercially for crop production, such as the alfalfa leaf-cutter bee (Megachile rotundata).

Top: A Megachile centuncularis at work. This is one of seven megachilid bees in Britain. Bottom: A leaf-cutter bee nest © Line Sabroe (top) and Subbu Subramanya, Wikipedia Creative Commons

In Ontario, Canada, alfalfa leaf-cutter bees have been creative and resourceful by using pieces of polyethylene-based shopping bags as a building material. Another local species, the bellflower resin bee (Megachile campanulae), constructs nests with plant resins instead of pieces of plants. It has no use for plastic bags, but polyurethane-based sealants, which are applied to the exteriors of buildings, offer a handy and abundant alternative. Some bellflower resin bees mixed this plastic product with natural resins to build their nests.

Brood cells partially constructed with polyethylene plastic bag fragments (L,) and polyethylene resin © MacIvor & Moore 2013, Ecosphere 4(12) art155

Rural areas are not exempt from the plastic deluge. In the Argentinian countryside, bits of greenhouse covers, agrochemical containers, fertilizer bags and irrigation hoses combine with ubiquitous shopping bags to deface the landscape. One bee, possibly an alfalfa leaf-cutter bee, took advantage of this clutter to do away with leaves or petals completely: she built an entire nest with pieces of two types of plastic.

Plastic brood cells (L) and pieces of plastic used in the construction of a leaf-cutter nest © Allasino et al. 2019, Apidologie 50: 230-233

We don’t know whether plastics have any effect on leaf-cutter bees. They may be neutral, or even beneficial; plastics may act as a barrier against fungi and parasites, which are important mortality factors for solitary bees. On the other hand, these impermeable materials may trap water and thus increase the brood’s susceptibility to diseases. 

By using plastics, bees have demonstrated their ability to identify alternative and convenient resources, and to adjust to changes in their environment. All the same, plastic nests are another troubling sign of a world living in the Anthropocene. From the Greek anthropos (man) and cene (new or recent), this unofficially labelled geological epoch applies to Earth’s history since humans started to have a significant impact on climate and ecosystems. It’s a new world of mass extinctions, deforestation, pollution, fossil fuels, and climate change. Perhaps leaf-cutter bees can adapt and even flourish in this world. We may do the same. Or not. 

Taynish: gold dust!

By Caroline Anderson

This blog covers two visits to Taynish over the course of a week.  The first visit was filled with delight as there was a nice selection of damselflies out, and one or two four-spotted chasers.  I was thrilled, as it had been SO cold this May!

Only a handful of butterflies around but managed to capture this Speckled Wood.   After a holiday weekend of hot weather there should be more butterflies for you to spot – lots of Orange Tips and Small Heaths – these are indeed very small but what they lack in stature they make up for in beauty.  You can get an idea of scale from this dandelion clock. 

One interesting discovery I made as I was rummaging about in the bog at the boardwalk, was this Longhorn Moth – I’ve only ever seen one before and it was during the previous week.   It’s a beautiful gold colour with the most extraordinary antennae.

The bluebells are stunning at the moment, and the air is heavy with their scent.  They are also a great attraction for the pollinator insects – though sometimes you just have to look quite hard for them. This is a scorpion fly making the most of the bluebell cover.

Unfortunately, there was a distinct lack of bees during both visits, I think everything is just a bit later in getting going this year because of the recent low temperatures.   But finally on the pink next to the shore there were one or two getting covered in the gold stuff.  

There was also this wee guy making the most of the pollen – absolutely lathered in it! 

Talking of the gold stuff – check this out!  There’s lots of this type of grass in flower just now – and if you give it a shake you can see the pollen flying out – no wonder my nose is running! 

However, despite the lack of bees during my visits, there is hope, thanks to Heather and Gordon!  

Heather and Gordon, who keep Taynish so special for us all, made some bee houses for our Taynish Trail, and these are now being occupied. If you are considering a bee house, please follow this guidance to assure bees’ health.

The red mason solitary bees pictured below were busily going in and out of the hotel and were an absolute joy to watch.  The holes the bees have been using have been marked to make observation less tricky (that’s what the black dots are next to some of the holes) this also makes photographing them much easier too! 

It’s Garden for Wildlife Week so why not give our pollinators a wee helping hand. Good luck and tag @scotpollinators know how you get on by posting pictures on twitter.

Alone in a crowded house

By Athayde Tonhasca

A hole in a stone wall on a busy street does not sound like a great housing choice, but it is a haven for the chocolate mining bee (Andrena scotica). You can find this bee in streets, gardens, parks and countryside across Britain at this time of year, even during this never-ending wintery spring. Like approximately 70% of the 20,000 or so known bees in the world, this species is fossorial (from the Latin fossor for ‘digger’), that is, it excavates a nest in the soil and spends most of its life underground. And like about 80% of all bees, it is solitary: each female builds her own nest chambers in which she stocks pollen and lays her eggs.

Although solitary, chocolate mining bees tend to nest near each other. Many other solitary bees do the same, sometimes forming nest aggregations hundreds strong. As far as we know, they don’t interact with each other. But chocolate mining bees have one quirk:  they often share an entrance to their burrows. Behind a communal gate and out of sight, each of several female bees constructs and provisions her nest. 

Chocolate mining bees’ communal nest entrance along a pavement © Athayde Tonhasca

These concentrations of bees frighten some people. Beekeepers and council officers have been summoned to deal with ‘swarms,’ only to witness the comings and goings of chocolate mining bees. Worse, people afraid of being stung or concerned about damage to structures have wiped out whole colonies with insecticides. But these citizens are mistaken on both counts. Like any other solitary bee, the chocolate mining bee is docile and never goes out of its way to attack people or animals; besides, her sting is too weak to penetrate human skin. And their nesting galleries are temporary and too small to cause any damage to a wall.

A group of chocolate mining bees hanging around a communal nest entrance © Athayde Tonhasca

We don’t know why some bees chose to gather together for nesting. It’s a risky strategy because these concentrations may lure parasites and predators, and this seems to be the case for the chocolate mining bee. Bees may aggregate out of necessity; a sturdy, long-lasting nest requires a specific set of conditions (soil texture, moisture level, temperature, inclination), so bees may have to share suitable but limited real estate. Aggregations may be a manifestation of natal philopatry, which is an animal’s tendency to return to its place of birth. Or it could be that bees are attracted to each other out of self-interest: by building on a good spot already discovered by a trail blazer, a bee saves time and energy that would be spent searching for nesting sites on her own.

Whatever the reasons for its communal living, the chocolate mining bee should be welcomed. This species is highly polylectic – it collects pollen from a variety of unrelated plants – so it helps pollinate a wide range of spring-flowering shrubs, trees and wild flowers. They are not put off by nosy humans, so if you find them going in and out of a crack in an old wall or behind a stone in your local park, stop and watch for a moment. Soon you may spot a bee sprinkled with pollen grains, which is a sure sign she has been hard at work providing for her next generation and assuring the reproduction of many of our plants.  

A chocolate mining bee with her ‘pantaloons’ (pollen brushes) covered with pollen © Dave Smith

Creating a buzz for pollinators

By Annie Robinson

X-Polli:Nation is an actionable citizen science project that cross pollinates ideas, methods and technologies for pollinator citizen science. X-Polli:Nation aims to create a ‘buzz’ for pollinators by supporting:

 ‘people’ to learn and protect them,

‘practice’ to improve citizen science tools and of course,

‘pollinators’ by creating more habitat and supporting campaigns for their protection. 

Whether you are gardener, teacher, online recorder, or someone new to the field, we welcome everyone to get involved.  Our online tools and downloadable resources provide a programme of activities to support learning, recording, planting, and communicating the importance of pollinators. There are also complementary worksheets and teacher guides and we have a teacher training workshop on the 26th May.  This short video gives an overview of the project. Please do explore our website xpollination.org or join the conversation online (@XpolliProject #xpolli) to find out more about the wonderful world of pollinators. 

We are currently working across the UK and Italy. To give you a taste of the activities, our new citizen science survey is based on the Pollinator Monitoring Scheme (PoMS) FitCount methodology and combined with our new AI species identification tool for bumblebees, collects valuable data on pollinators and their foodplants. Citizen science data feeds into our Planting for Pollinators tool to provide species-specific planting advice for certain species of bumblebee. Our Pollinator Promise campaign can be used to encourage your local community to protect pollinators.  Whether you have 5 minutes or 5 hours to delve into the world of pollinator citizen science, want to be desk based or out in nature, we have a full programme of activities around the citizen science cycle below:

Learning about Pollinators 

XPolli:Nation has lots of resources for learning (& teaching) all about pollinators. 

Bumblebee and Butterfly Training tool

You can discover how to identify pollinator species through our interactive bumblebee and butterfly training tools. You will see a series of photos that you can practise identifying to species level using our interactive feature keys, with help from artificial intelligence technologies, including automated image recognition and automatically generated feedback on your attempts. There are varying difficulty levels so its suits whatever level you are at. It’s great fun testing your identification skills. 

Pollinator Open Learn Create course

Or if you are just after a course giving an overview of what pollinators are, why they are important, why they are under threat and what we can do to help we have created an Open University course that is free and accessible to all. 

Recording Pollinators

We would be delighted if you take part in a citizen science survey and contribute valuable new data about vital insect populations and their habitats.

There are two steps:

Citizen Science Survey: We have teamed up with the Pollinator Monitoring Scheme (PoMS) – which provides data for UK Biodiversity Indicators – to create a survey where you can count the number of insects in different groups (e.g. bumblebees, beetles, butterflies etc.) visiting a patch of target flowers for 10 minutes.

Photo-Record Submission: While taking part in the survey or at any time, you can take photos of bumblebees and submit to our dedicated recording scheme Planting for Pollinators, where you will be guided by technology to help identify the species (e.g. Red Tailed or Buff-Tailed Bumblebee etc.).

Planting for Pollinators

Ever wondered what you can do in your own garden or local green spaces to help pollinators? Explore which plants support different species of pollinators throughout the season using our Planting for Pollinators tool. 

Communicating the Importance of Pollinators

I imagine lots of you do this already but inspiring your friends, family and others in your community to protect pollinators can make a real difference. 

There are two parts to the Communicate activities: 


1. Making a Pollinator Promise: When you sign up to the Pollinator Promise, you pledge to plant a pot or put aside a 1 x 1 metre area in your garden, school grounds or business to grow pollinator-friendly plants. The Pollinator Promise was started by pupils at St. Alban’s Primary Church of England Primary School. They asked their parents, friends, local businesses and community groups to sign up.  You can watch a video here

2046 Polli-promises have been made so far to create 4820 square metres of pollinator-friendly habitat. The pupils at St Alban’s hope to spread the Pollinator Promise campaign throughout the UK, and they are counting on your help. Wouldn’t it be brilliant if we could get more dots on the map in Scotland!  Sign up here

2. Designing your own Campaign for Pollinators: We also encourage you to come up with your own creative ideas about how you can spread the message to protect pollinators and share these on our social media account (@XpolliProject #xpolli #pollipromise)

Please do explore our website xpollination.org or join the conversation online (@XpolliProject #xpolli) to find out more about the wonderful world of pollinators.  If you are a teacher join us at the teacher training event on the 26th May

Thick-headed undertakers

By Athayde Tonhasca

If you watched the film Alien and jumped out of your seat when the creature burst from the unfortunate astronauts’ chest, an entomologist in the audience may have nodded knowingly: ‘Ah, a human parasitoid!’ Indeed, the screenwriters acknowledged entomological inspirations for the alien’s life cycle. 

Here on Earth, a parasitoid is an insect that is free-living as an adult, but completes its larval development inside the body of a host (usually another insect), eventually killing it. A female parasitoid lays her eggs on or inside the host; the eggs hatch and the larvae consume the host. This type of life history lies between a predator’s and a parasite’s: a predator such as a dragonfly takes several prey and kills them outright, while parasites such as lice, fleas and ticks live off hosts without killing them.

Most parasitoid species are wasps, followed by flies. Among the latter, there are about 800 species (24 in Britain) of thick-headed flies, also known as bee-grabbers or conopids (family Conopidae). Many conopid species look more like wasps, bees or perhaps hoverflies. The size of their heads is another noticeable feature, which explains their common name.

A conopid fly © Fir0002, Wikipedia Creative Commons

Thick-headed flies hang around flowers, mostly between June and August. Sometimes they are looking for a sip of nectar, but if a female is lurking, she may be waiting for an opportunity to lay her eggs. Which is bad news for a visiting bee or wasp, and in some cases for crickets or grasshoppers. 

It goes like this: an unsuspecting bumble bee approaches a flower. A female conopid closes in and grabs the bee in mid-air. Still afloat, she pries open the bumble bee’s abdominal segments with her theca, which is a pad-like, hardened structure at the end of her abdomen. Sometimes attacker and victim fall to the ground, but the outcome is the same; the female fly lays a single egg inside the bumble bee and lets it go.

A female conopid with her menacing theca clearly visible © Hectonichus, Wikipedia Creative Commons

The drama is over within seconds, and both insects fly away. The fly will wait for another opportunity to attack. But the bumble bee is done for.

The egg hatches and the larva develops inside the bumble bee, consuming its innards. But the larva does not penetrate the host’s thorax, thus keeping her flight muscles intact. The bee carries on with her life, feeding and taking nectar back to her nest, although less and less efficiently as the parasitoid grows. Within 10 to 12 days, her abdomen is completely taken up by the larva, which has nothing more to eat. The bee dies and falls to the ground (if you find a dead bumble bee with a swollen abdomen, conopid parasitism could be the causa mortis). The larva pupates and overwinters inside the bee’s body, and the adult emerges in the following year.

A conopid cocoon lodged inside a bumble bee’s abdomen © Abdalla et al. 2014. Revista Brasileira de Entomologia 58: 343-348

Conopids are among many species of parasites and parasitoids capable of changing hosts’ behaviour for their own benefit. There are examples of wasps that turn ladybirds into inert bodyguards over parasitoid eggs, and fungi that make ants climb up plants so they can release spores. Perhaps the most notorious case is the effect of toxoplasmosis cells on rats and mice. Infected rodents become attracted to cat’s urine and are less likely to hide. This altered behaviour is a death wish: they became easy prey for cats, in which toxoplasmosis cells complete their development. See other examples here.  

Some conopids increase the chances of their pupae making it through the winter with a trick that may seem macabre to human eyes: they induce their bumble bee hosts to dig their own graves. In America, bumble bees parasitized by the conopid Physocephala tibialis bury themselves in the soil just before death. This grave-digging behaviour does not make a difference for the doomed bee, but it shelters the parasitoid pupa from cold and dehydration during winter months, and reduces its exposure to pathogens and its own parasites. Hibernation in the soil also leads to larger and healthier adult flies.  

The grave-digging inducer Physocephala tibialis © Beatriz Moisset, Wikipedia Creative Commons

How common are conopid attacks against bumble bees? Accounts differ: in Britain, parasitism rates vary from 13 to 30%; in America, local figures can reach 80%. But bees don’t take it lying down. When parasitism pressure becomes high, some bumble bees shift their reproduction cycle to later in the year to avoid peaks of conopid populations. And bees have an immune system against invasive agents. Some bumble bees – like many other insects – secrete melanin, which encapsulates and suffocates the parasitoid larva. Some studies have shown that melanisation kills up to 30% of invading conopid larvae. 

We don’t know the consequences of conopids for bumble bee populations, but parasitism is a fact of life for every insect. About 10% of all known insect species are parasitoids, although specialists believe this figure is a huge underestimation. 

Parasitism seems gruesome and cruel. Even Darwin was dismayed by it, as he expressed in one of his letters: ‘I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidæ [ a group of parasitic wasps] with the express intention of their feeding within the living bodies of caterpillars.’ But such anthropomorphism (attribution of human values to natural phenomena) is misguided and biased. Parasitoids, like predators and parasites, are important regulators of the natural world: they prevent excessive population growth, including of agricultural pests and disease vectors. Parasitism helps shape biodiversity and ecosystems, so it is not intrinsically bad or good. It is a characteristic of life on our planet.

Making wildlife connections at Dance Connect

One of the biggest challenges facing emerging pollinators each spring is finding food. What we plant in our gardens, parks and around our workplaces can be a huge help for foraging insects. So take a bow Dance Connect in Kinross who have skilfully transformed the area around their dance and fitness studio into a pollinator-friendly hot spot.

Inspired by the work of the energetic Kinross-shire Raingardens Challenge, Dance Connect have combined choreographing a pollinator banquet with improving the environmental and social value of the area on their doorstep.

There are certainly multiple benefits in what Dance Connect have done.  First and foremost their actions are great news for local nature, however their approach is also creating an attractive environment for people to admire, which acknowledges the recognised links between health and well-being and the natural world. It’s what PR gurus at one time labelled a ‘win-win’.

So how did this project to transform the area around the studio come about?

When Dance Connect purchased their site from Perth and Kinross Council the swales and much of the willow planting, which fringe their car park, were already in place. However, there was an opportunity to make more of the site, to better protect the swales, and extend the planting.

Swales should not be undervalued. Nowadays, we often experience water in our towns and villages as a problem: flooding property or roads, bubbling up from overloaded sewers in wet weather. 

One of the attractive characteristics of a swale is channelling and making use of heavy rainfall. Well-designed swales take the peak flow of rainwater and only slowly release it; in that way they help manage flood risks. The water seeps into the ground in a more controlled fashion, and it is worth adding that beyond potentially reducing the instances of flash floods, a swale can also help plants survive during dry spells. 

However, the swales at Dance Connect were likely in time to be damaged by cars, the soil was susceptible to being compacted, and surrounding plants in danger of being crushed. It was the clever management of willow planting around the swale, allowing the subtle presence of overhanging soft willow branches to fringe the car park edges, which helped demarcate the swale and protect it from compaction and damage.

The good work doesn’t stop at the car park edge. Additional planting beyond the car park borders stretches up nearby banking to impressive hawthorn and a few conifers (including a young Scots pine which will become an impressive tree in due course). Across from the studio’s entry driveway is a flat area of open grass which it is intended to make into a wildflower meadow.

So the Dance Connect surroundings became a multi-functional project, capable of helping nature (the emerging bumblebees on the willow catkins being a great example), mitigating against heavy rainfall incidents, and providing a natural and pleasant arrival point for visitors. 

Co-owner Rachel has certainly been busy adding to her banquet for bees, and along with Jane Shields of Living Water, who is also an ecological designer for the Kinross-shire Raingardens Challenge, planted woodland wildflowers into the willow area, starting with foxgloves at the margins. A few red campions were growing on the site already and more have been established now in the edges of the willow woodland, with lesser celandines adding vibrant early spring colour in the wetter soil in the base of the willow swale. 

Nature rarely stands still. The original mulch covering the soil beneath the trees has long gone, and grass, nettles and docks are beginning to colonise the area. The aim now is to try and create a more varied, beneficial and interesting woodland floor.

The work to enhance the natural features around the studio will continue for some time. The diversity of the grounds certainly increases interest for visitors and passers-by alike, and if you visit you won’t be the only one enjoying the experience. As we head through spring and summer – a range of pollinating insects are sure to make their moves around Dance Connect.