Tiree’s Great Yellow Bumblebee project revisited

By Janet Bowler

In my previous blog about ‘Tiree’s Great Yellow Bumblebee Project’, I described how residents of all ages on the Isle of Tiree in the Inner Hebrides established a community project to help protect an important population of the UK’s second rarest bumblebee – the great yellow bumblebee (GYBB) Bombus distinguendus. 

Great Yellow Bumblebee on phacelia (C) Amy Millard

Through planting areas of ‘mini-machairs’ and GYBB ‘super-food’, conducting bumblebee surveys and holding bumblebee events, the species has benefitted from increased foraging habitat, greater local knowledge and awareness of the species’ status and needs, and a sense of community ownership. That was in the first half of the project (2017-2018).

Great Yellow Bumblebee (c) Andy Robinson

In the second half (2019-2020), the project is still going strong and developing in new ways. We continue to plant new areas of forage and monitor the success of plantings, continue to conduct bumblebee surveys, and are creating a storybook for children.

Sensory machair 2019

Sensory machair 2020

We were delighted when staff at Tigh a’ Rudha, the local Eventide Care Home, asked us to get involved in the creation of a Sensory Garden for the residents. The garden was constructed in two parts; an area of formal raised beds with bright garden flowers and visual and tactile objects, and a more natural area of wild flowers to attract bumblebees and butterflies. It is our hope that by next summer, the Home’s residents will be able to enjoy the sights, sounds and smell of the machair again.

The total number of GYBBs counted during surveys in 2019 was 220. Although fewer than 2018’s extraordinary count of 370, it does not necessarily mean that there were fewer GYBBs around. The totals partly reflect the amount of effort put into searching for them, and it won’t be until we have calculated the number of bees seen per observer hour, that we will be able to make comparisons between years. We plan to do this at the end of this year once all the survey data are in for the period 2017-2020.

Jeannies mini-machair patch

Last summer’s weather boosted growth of the GYBB’s main forage flowers. The machairs were lush with red clover and other key flowering plants, in densities not seen on the island for some years. It was extraordinary and commented upon by many of the island’s older residents.

Sandaig machair

With such abundance of forage during the busiest period of the GYBB’s breeding cycle, we were optimistic that 2019 would be an excellent year for GYBB population growth, and that more daughter queens would survive into the following spring. And it looks as though this may be proving true. At the end of last month (June 2020), when hibernating queens first emerged from their winter burrows, we recorded more queens than ever before. A record-breaking 12 queen GYBBs were spotted in one hour in an area of dense kidney-vetch flowers. Normally, we would be satisfied with 2-3 queens in one hour! Will this summer’s surveys provide one of the highest counts ever?

A draft book scene (C) Rou Worsley

Last, but certainly not least, a group of children from Tiree Primary School have written a storybook for children in Gaelic and English about the life of a queen GYBB and her struggle to raise a family. The children have created fun characters and a lively plot that ingeniously weaves in a conservation message about the relationship between machair habitat, human intervention and the species’ survival.

A local artist is transforming the children’s concepts into striking illustrations, and older Gaelic speakers from the community are helping with translation. We are enormously grateful to The Gaelic Books Council, RSPB Scotland, Tiree Association, Paircwood Publishing, Tiree Community Windfall Fund and a private donor, whose donations are making all this possible. The book launch is planned for this coming November.

Great Yellow Bumblebee on dandelion (C) John Bowler

 

What a difference a week makes!

This month I had two visits to Taynish NNR within the space of a week and they couldn’t have been more different, writes Caroline Anderson.  The first visit, on the 4^th of July followed a period of torrential rain and pretty well everything was taking its cue from this moth:

However, there were lots of beautiful flowers with their “open for business” signs out, so I knew it wouldn’t be too long before the pollinators started to appear. Tentative flutterings from some of the resident butterflies caught my eye, Ringlets and Speckled Woods, although a bit battered from the rain, were bravely emerging.

Then it was the turn of the damselflies and bees, beautiful Emeralds and Blue Tails jewel-like amongst the long grass.

Move on a week and the story is even better.   You know its going to be a good day when one of the first things you see are the lizards basking on the boardwalk.  Very cautious and darting off at the slightest movement but managed to catch this wee one scoping its territory.

The boardwalk is definitely one of the special areas to visit when you come to Taynish, if it’s not covered with dragonflies, damselflies, lizards and toads you have the chance to enjoy the beautiful waterlilies which are in full bloom just now.

I didn’t have to wait long before being joined by this beautiful Four banded Longhorn beetle who flew in and dropped down beside me.

On down to the Mill where the beautiful long grass is a haven for some of the most effective pollinators.   Hoverflies, moths, bees and damselflies are only a few of the special visitors to be seen.

This Common Darter was eating its lunch on one of the picnic benches – it was hard to tell what it was having as only the legs remained!  Very gross and very cool at the same time.

So even though a week separated my visits, in very different weather conditions, there was still lots of activity,  I just had to look a little harder during the first visit.    So when you visit Taynish and you can’t see anything, just sit, and watch, they will come – I promise!

Too hot to handle (III) – climate change and bumble bees

By Athayde Tonhasca

As we have seen, many insect species are responding to a warmer planet by scampering to higher latitudes or elevations to stay within their range of temperature tolerance. However, bumble bees do not seem capable of upping sticks. Long-term observations tell us that most European and North American species are not dispersing beyond the northern borders of their ranges, while some species are becoming scarce in their more southerly territories. So the chances of a bumble bee occupying a given area in North America have dropped by 47% from the period 1901-1974 to the period 2000-2014. In Europe, the chances have fallen by 17%.

We don’t know why bumble bees are not tracking climate change by expanding north. It could be a lack of suitable plants beyond their historical ranges, or because they respond more strongly to factors other than temperature, such as day length. It could be something else, or a combination of factors. But as bumble bees are not adjusting their distributions, they would have to adapt to warmer conditions, which does not bode well for them.

The body temperature of a bumble bee at rest is close to ambient, like most insects. But to generate the power needed to lift off and sustain flight, bumble bees need to raise their temperature to above 30°C, which they do by rapidly contracting their flight muscles and by enzymatic reactions not completely understood. All this generated heat allows bumble bees to live comfortably in temperatures that would be intolerable to other insects: you may have seen bumble bees busy at work on chilly, drizzly mornings. Moreover, their chunky bodies are well insulated by thick hairs, and black body segments help absorb heat.

This sleeping bumble bee has to warm up to 30°C to become active. © Athayde Tonhasca.

These thermoregulation adaptations help explain why bumble bees are most abundant in the temperate regions of the Northern Hemisphere. Species like the aptly named Bombus frigidus ranges all the way to Alaska, while Bombus polaris can live above the Arctic Circle and forage at near freezing temperatures.

The downside of being adapted to the cold is the risk of overheating. For a bumble bee, it doesn’t take much to go from an optimal high temperature to a lethal high temperature. So they prefer to forage in the morning, with the peak time from 7 to 8:00 h for some species. And being too hot to function is not the only problem in a warmer environment: pollen and nectar may become scarce, available at the wrong time, or altered in their nutritional value.

But apparently it is not so much the increasing average temperatures that are harming bumble bees, but rather the number and intensity of extreme weather events such as droughts and heat waves. Bumble bees are disappearing more quickly from places with higher frequency of sharp swings in temperature or precipitation.

Can we stop or revert this trend? It would be difficult without a global reduction of greenhouse gas emissions, but mitigating measures are possible. Landscape management aimed to protect or improve bumble bee habitats could facilitate the colonisation of new areas. Creation of habitat corridors could help the move, although this method has had mixed results for a range of animal species. Species could be translocated to new areas, a measure that needs to be carefully assessed because of the risks to the existing fauna: the newcomer may outcompete them, or bring new pests and diseases.

Mitigation is complex and costly, but the risks of not addressing climate change are the loss of important pollinators and some of the most recognisable and loved features of the British landscape.

 

Too hot to handle (II) – climate change and pollinators

By Athayde Tonhasca

The life of an insect is regulated by seasonal episodes: hatching in the spring, foraging in the summer, going into hibernation in the autumn, and so on. These biological phenomena correlated with climatic conditions are known as phenology – the term also refers to the study of such events. Plants have their own calendar, which includes the interval of time when pollen and nectar are produced. So pollination requires an overlap of phenologies: pollinators must be flying and flowers must be blooming at the same time. All of this sounds a bit mundane until we consider the possibility that these temporal windows no longer match.

The timing of life cycle events is changing rapidly in response to climate change. From long-term recording schemes in Europe and North America, we know that many birds, moths and butterflies are becoming active, migrating or reproducing earlier in the year. In the UK, plants are flowering earlier, and bumble bees have advanced their spring activity by about two weeks from 2001 to 2007. If phenological changes for plants and pollinators happen at different rates or magnitudes, they may become out of sync. For flowers, there will be reduced visitation rates and pollen deposition; for pollinators, there will be less nectar and pollen.

The right place and the right time for pollinator and flower © Pauline Smith.

Fortunately, most pollinators visit multiple plant species, and plants are visited by multiple pollinator species. Alternatives makes pollination flexible, and that’s possibly why we don’t know of any case of pollination failure because of life cycle asynchronies. However, things could change if phenologies are pushed even further apart.

But there is more to it than mismatched life events. If air temperatures become too high, some pollinators may forage only during early mornings and over shorter distances. Consequently, flowers that open later in the day could be less visited, and some not visited at all. Pollinators may end up with fewer options because warmer, drier summers reduce flowering. Or flowers may be missed altogether: pollinators find far away plants by picking up their scents. But if these scents have their chemical composition altered, they may no longer be recognised by pollinators.

These scenarios are not wild speculations, but possibilities grounded in research. We cannot predict the magnitude of climate-induced effects on pollinators because of our poor understanding of the processes and variables involved, let alone the fact that responses have been far from uniform. Data from the last 35 years or so have shown phenological shifts, but no consistent trends: the seasonal timings of some interacting species are now closer together, while others are further apart. What we can say for sure is that there are more than enough signs of rapid and profound change; pollinators and pollination services are likely to be disrupted.

There is one group of pollinators whose responses to climate change we understand a little better: bumble bees. We will discuss them next time.

 

Too hot to handle – climate change and insects

By Athayde Tonhasca

The body temperature of most insects is approximately the same as that of their surroundings. They are poikilothermic, or ‘cold-blooded’, animals. So the warmer it gets, the more active insects become; they feed more, mate more frequently and lay more eggs.

You can see where this is going. Could global warming be good for insects? To a point, yes. In a warmer planet, diapause (the period of suspended development) will terminate earlier, winter mortality will be lower, spring will come sooner and summers last longer. Most insects will have more time for developing and dispersing.

But before you start singing the Ode to the Coal Power Station, remember that less desirable insects may benefit as well. Numbers of crop pests with high reproductive potential such as aphids and thrips could explode; forests in Scandinavian countries are already facing severe damage by insect outbreaks. Invasive disease-carrying species – affecting humans, livestock and plants – may no longer be killed by the cold weather.

Mild winters allow more pine beetles to survive and kill large swathes of forest in Colorado, USA. The image is in the public domain.

Most insects benefit from higher temperatures, but not all: some, like bumble bees, apparently already live close to their upper levels of tolerance. As temperatures rise, these species are forced to follow shifting cooler habitats by moving towards the poles or to higher altitudes. Indeed, the abundance of many butterflies, beetles, dragonflies, grasshoppers – and plants as well – have contracted at low latitudes and elevations, and increased in more northern and elevated regions. Species incapable of dispersing or which are isolated in pockets of habitats are stuck, and eventually may vanish. In Britain, local populations of cold-adapted butterflies with narrow temperature tolerances have disappeared. As far as we know, no species has gone extinct because of increasing temperatures, but the risk is real.

As the overwhelming majority of reputable climatologists have predicted, the rise of greenhouse gases in the atmosphere is not only turning the world warmer, but also changing precipitation patterns and increasing the frequency of extreme weather events. There will be more and stronger droughts, floods, tornadoes, cyclones and other dangerous, traumatic and costly weather-related phenomena.

Scientists have been looking for possible consequences of these factors to insects, particularly agricultural pests, and they have come up with a maze of scenarios. Plants suffering from water stress during droughts are more vulnerable to damage by herbivore insects, but some of these pests do not survive droughts. A rise in atmospheric CO₂ enhances crop photosynthesis thus plant growth and crop production, but it also increases the carbon to nitrogen (C:N) ratio in plant tissue. Insects need nitrogen for protein, so herbivore species have to eat more to compensate for plants’ reduced nitrogen content. But higher C:N ratios slow their development, making them vulnerable to natural enemies for longer. On the other hand, higher temperatures reduce the length of larva and nymph stages, which are the periods of greater exposure to predation. So plant feeders may have a greater chance of escaping natural enemies. The life cycles of plants, the insects that feed on plants, and those insects that feed on the plant feeders, may get out of sync if they respond differently to higher temperatures, with unknown and unpredictable consequences.

Does all of this sound complicated? Well, there’s more.

Diapause is one the most important events in an insect’s life – it allows it to survive unfavourable conditions, which happens during the winter in temperate regions. Diapause is regulated mostly by photoperiod, which is the daily period of light. When the days shorten, insects start to prepare for the onset of winter; when the days lengthen, insects become active again. Photoperiod is a reliable clue because it does not depend on the weather; it follows a stable pattern. The problem is that for many species, photoperiod is not the only trigger for diapause: they may respond to temperature and sometimes to precipitation as well. As we have seen, this is risky in a world changed by climate. The mismatch between temperature and photoperiod cues may induce insects to enter or leave diapause too soon or too late, with potentially disastrous consequences for their development, reproduction, and survival.

We have a vague, unsatisfactory grasp of the effects of climate change to insects, but the few data available tell us that trouble is brewing. And risk to insects means risk for us, since we depend on so many of their ecological services such as maintaining the food chain, decomposition, and recycling of organic matter.

And how about the effect of climate change on pollinators?

We will leave that for next time.

(This is the first in a trio of articles by Athayde looking at climate change, insects and pollinators)

Marmalade hoverflies, the unbeatable frequent flyers

Soon during a stroll in your garden or local park, you will see lots of flies striped orange and black hovering over flowers like tiny helicopters, writes Athayde Tonhasca. These are marmalade hoverflies (Episyrphus balteatus), which are some of the most conspicuous and familiar insects in gardens and indeed many other habitats. They are widespread throughout Europe, North Asia and North Africa.

The marmalade hoverfly and related species (family Syrphidae, aka syrphid flies) are mimics of bees and wasps; in fact, is not uncommon for people, tricked by the flies’ ruse, to step back from these harmless insects.

Adults feed on pollen, nectar and honeydew from a range of plant species, while larvae feed on aphids – entomologists say they are aphidophagous. Females smell aphid colonies and lay their eggs in the middle of them. The larvae hatch immediately, and each devours up to 300 aphids per day until pupation. So you could say these flying morsels of marmalade are important allies of gardeners and farmers.

A marmalade hoverfly larva © Entomart, Wikipedia Creative Commons.

Some people will be surprised to know that these fragile insects embark on migrations that may cover thousands of miles. Each autumn, marmalade hoverflies and other migratory syrphids head south to spend the winter in southern Europe and the Mediterranean. Their offspring move northwards in the spring, lay their eggs, and the new generation sets out the cycle again. To survive these hazardous journeys, hoverflies climb to high altitudes, where strong tailwinds take them to their intended destination.

Some years, they arrive in Britain in large numbers. And “large” is an understatement. By using specialised radars designed for monitoring insects (Vertical-Looking Radars or VLRs), researchers have estimated that up to four billion marmalade hoverflies along with the aptly named migrant hoverfly (Eupeodes corollae) cross the English channel to and from Great Britain every year. This represents 80 tons of biomass. If you are impressed by these figures, you should know that hoverflies account for a fraction of insects’ latitudinal migrations known as “bioflows”: about 3.5 trillion insects, or 3200 tons of biomass, migrate into southern Britain annually. Insect bioflows pour vast amounts of nutrients (particularly nitrogen and phosphorus), energy, prey, predators, parasites, herbivores and pollinators into our ecosystems. But we have only a vague understanding of their impact on food webs and local species.

The marmalade hoverfly does not stand out as a particularly efficient pollinator. It is small and not very hairy, a negative mark for joining the pollinators club because pollen transport depends on abundant body hair. Even so, this fly is known to improve the yield of strawberries.

Each marmalade and migrant hoverfly carries an average of 10 pollen grains from up to three plant species in their journey into Britain. These are not impressive figures when compared to bees, which return to their nests loaded with pollen. However, considering the massive number of flies and the wide range of flowers they visit, a grain of pollen deposited on a flower here and there must add up quickly. We just haven’t paid much attention to these unpretentious pilgrims.

On the verge of success

During the recent pandemic one thing that people have noticed, and increasingly appreciated, is the fact that so many of our verges haven’t been cut. This has been good news for flowers, bees and butterflies. What’s more many verges have become a visual feast which we can all enjoy.

The way we manage our verges is clearly changing.

Riverside Drive, Dundee

Social media was awash with images of floral diversity during lockdown as many councils directed their resources to other areas, or simply couldn’t follow their usual cutting regimes. Of course this may have simply emphasised a change that was already underway, Across the UK a number of councils are have been altering their mowing regimes in a way that maximises opportunities for flowers and pollinators to thrive.

Historically the primary driver behind mowing verges seems to have been linked to seeking to comply with the Highways Act. There was also, in the minds of some, a perception that an unmown verge looked untidy or messy. So the safety angle got mixed in with a notion of civic pride, and hence verges were often mown when really they could have been managed with an annual cut and lift regime. That would undoubtedly have helped nature and saved councils money, and if explained as such quelled any notions of civic abandonment.

But change is gathering apace, and complementing a reduction in mowing of verges there has also been a shift away from 100% mowing of amenity grassland in cities, towns and villages.  A more selective approach is gaining momentum. Thus it is increasingly common to see a mown strip around the edge of urban patches of grass, or a mown path emphasising a desire line through an area of longer grass. Both actions taken in a spirit that is practical for ease of use, sensible in terms of cost of management, and a benefit for biodiversity.

University of Strathclyde, showing a short mown area for ease of access.

A narrow strip either side of the Perth cycle path near Muirton

Taken as individual approaches these are great advances. Viewed in aggregate they can help build up to a wildflower corridor approach.

In the Perth & Kinross Local Authority area the council have gone a step further.  Working with the Tayside Biodiversity Partnership and the Perth and Kinross Biodiversity Ambassadors, they are looking to survey the difference between areas of grass normally cut by the council against those which have not been cut during the Covid-19 crisis.  This will give them a clearer measure of what the differences in management styles deliver for biodiversity.

The survey is easy yet comprehensive. Preferably participants should select two area of grass, each over 1m square. They should aim for one area which has not been cut during the Covid-19 crisis, and one area which has continued to be mown. If they cannot find an area which has been mown, they are encouraged to concentrate on a site that is unmown.

A series of questions are presented in an easy to follow table. To illustrate some of the findings the public are encouraged to submit photographs as part of their submission.  This visual approach will complement the short, yet cleverly crafted, survey form in which around a dozen questions are listed. These range from noting wildflowers present, counting the variety of flowers, stating bees and butterflies seen, through to noting the perceived appearance of the area.

That latter point is an important one. There is a perception with some members of the public that unmown areas can look abandoned and unkempt, almost unmanaged.  That’s why at Scottish Natural Heritage the Pollinator Team produced a ‘Managed for Wildlife sign’.  These are free for any council to display in unmown areas to let the public know that the area is indeed being managed for the benefit of wildlife.

It is a great credit to the Perth and Kinross that they are going down this route in such an engaging and open fashion, but perhaps not a surprise. Visitors to the River Tay who walk north towards the meeting of the River Almond with the Tay will have noticed how flower-rich the river defences are. Here the defensive banks are not nutrient rich and as a result a host of wildflowers have flourished. What’s more the banks are sensitively managed for nature; allowed to flower through summer and set some seed, before receiving an autumn cut.  This programme ensures the banks continue to look good year on year.

The twin threats of climate change and biodiversity loss coincide with a period in which we are increasingly realising that we need to have a nature rich future if a green recovery is to take place. We are also enjoying the mental and physical benefits that a healthy natural world can offer.

How our local authorities manage their areas of grassland has the potential to play a small yet very visible role in this process, and in taking actions on our doorsteps they can both help wildlife and galvanise increased support for helping nature.

The old joke used to say that “Perth is the smallest place in Scotland. Why?  … because it lies between two Inches!”  Clearly however this is an area where the biodiversity team think big, and that’s a wonderful punchline for nature.

 

Participants in the survey should email their completed sheets and photos to JoannaDick@pkc.org.uk

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Seizing opportunities, big and small

Recent months have been a sobering experience. Many of the things we took for granted suddenly disappeared.  The view outside our window, the greenspace in our local community, filled a huge void. Simultaneously, an appreciation of the role of nature in improving our mental and physical wellbeing became mainstream.

Meadow sown in derelict sewage works tank (Pictures courtesy of Mark Brand)

Whilst the Covid crisis has been in everyone’s mind, lurking in the background are the twin threats of climate change and biodiversity loss, and they won’t play second-fiddle for long. Scotland’s Local Authorities are responding to these two issues, and their biodiversity work has produced encouraging social benefits.

In speaking to Mark Brand, a Planning Officer with East Renfrewshire Council, it is heartening to hear of the strides his Local Authority has made in developing new approaches to tackling biodiversity loss. The way that they manage green spaces in particular has been under near constant review and progress can be measured both in the short and the long term.

Take a small project just completed in the village of Waterfoot (which lies between Eaglesham and Clarkston). A community greenspace has been created next to an area of new housing. At first glance the space looks conventional, with the typical mix of play equipment, benches and a small AstroTurf area you might expect.

A five hectare derelict site two years after sowing.

However, the Council has sown a short meadow mix instead of the usual ryegrass amenity seeds. This will provide a feeding stop for a host of pollinators and, managed sympathetically, it may do so for years to come. What’s more, it will be nice to look at, thus creating a joint ‘for people and pollinators’ benefit.

And it isn’t just the creation of a valuable foraging area for pollinators that impresses. It’s the realisation that managing sites for the long run can make for an easier journey. By following a relaxed mowing timetable the grassland flourishes during spring and summer, and the flowering season is maximised during pollinators active-lifecycle. And cutting the grass annually makes the area less likely to become dominated by a few species.

Changing mowing regimes is a hot-topic these days, as is cutting short grass-paths for easy access whilst letting meadows thrive.   Hand-in-hand with introducing these pragmatic approaches comes an education and information role which lets the public know that relaxed mowing isn’t down to untidiness or laziness, rather it’s about making a choice in favour of giving biodiversity a helping hand and better managing our assets for the nature we love and need.

Phil Collin’s famously sung about how you ‘Can’t Hurry Love’ and certainly people promoting these sorts of greenspace changes would sympathise. They know that good things don’t always happen overnight. Instead there usually has to be a period of conversation and persuasion before there is acceptance of a change of tack. One point however may prove the clarion call for change – reduced mowing results in financial savings.

In the same vein, East Renfrewshire Local Authority deserves credit for swapping the usual mix of landscape trees for fruit trees in Waterfoot. In doing so they created a small community orchard space with about 20 varieties of fruit trees. These can provide an early source of nectar and pollen for emerging insects in spring. And there’s more. The subsequent fruit is a welcome bonus for local residents (and birds!). It’s a classic ‘win-win’ scenario.

And good news spreads.  Mark recently noticed that house builder Taylor Wimpey will be using the same ‘Waterfoot’ Scotia seeding mix for the greenspaces in their latest development in Barrhead.

There was a time when Barrhead was associated with large industrial sites belonging to the likes of Armitage Shanks and Nestle. Now, as a post-industrial future takes shape, land is being converted to different uses, some of which are rich in opportunities. Sometimes those opportunities are temporary.

With that in mind, back in 2016, just over five hectares of meadow were sown on derelict land on the edge of Barrhead.  The land had been vacated by Nestle’s Purina Factory, but being relatively flat and enjoying good access was always likely to be earmarked as a development site. Nevertheless, as a vacant site it was an interim opportunity for helping nature. Development looks likely next year but this temporary greening project has had a good run.

Sowing gets underway in 2016

The moment was seized, and a fleet-footed project saw seed sown on a crushed demolition substrate (which had been farrowed to break up compaction). There was never any certainty as to how long it would last, but a full five years on it is a source of comfort that this short-term opportunity was snapped up. On a hot summer’s day it positively vibrates with insect noise and is a vital refuge for all sorts of wildlife.

Kidney vetch is dominant on very rubbly crushed demolition ground

The value of outdoor space, for nature and people, has rarely been higher on the agenda. In East Renfrewshire, the Local Authority has seized opportunities with considerable imagination. It bodes well for the future, and the new normal.

 

The birds and the beetles: the rowan tree’s facts of life

The rowan tree (Sorbus aucuparia) has deep roots in Celtic folklore, thanks mostly to its bright red berries, which have long been associated with spirits and all things magic. But never mind the myths; the rowan is a ubiquitous feature of the British landscape, and has an important ecological role to play, writes Athayde Tonhasca.

Rowan berries © Lorne Gill

The rowan is found in most parts of Britain, reaching altitudes close to 1,000 m in the Scottish Highlands. It is not finicky about its habitat, as long as the soil is well-drained; it grows on abandoned mines and wasteland, as well as rocky slopes and cliffs, crevices in rock outcrops and on top of boulders.

The sweet, heavy smells of rowan flowers are quite attractive to insects, particularly flies. But this tree may be an oddity; it appears to be primarily a cantharophilous species. Cantharophily, from the Greek kántharos (beetle) and philos (loving), means pollination by beetles. Not many plants are fully cantharophilous, although beetles were important pollinators for the earliest flowering plants during the Mesozoic (about 200 million years BC), long before bees came along. Today, many primitive species such as Magnolias are pollinated by beetles.

Beetles do not have the subtle approach of bees, flies and moths. They plough through flowers eating nectar, pollen, petals and leaves, defecating as they go. They often spill more pollen than they eat. That’s why they are called “mess and soil” pollinators. Click beetles (Elateridae), scarab beetles (Scarabaeidae), sap beetles (Nitidulidae), leaf beetles (Chrysomelidae), rove beetles (Staphylinidae), blister beetles (Meloidae), and long-horned beetles (Cerambycidae) are known to feed on flower parts.

Click beetles visiting flowers © gailhampshire, Wikipedia Creative Commons

The pollen attached to their bodies fertilises quite a few rowan berries, which are eaten by a variety of birds. In fact, the rowan is one of the most important food sources for fruit-eating birds in northern Europe.

Rowans produce large crops of seeds in some years (plant ecologists call it ‘masting’), and very little to almost none in others. The availability of rowan berries affects the annual distribution and migratory behaviour of birds on large scales. For example, the location and abundance of bullfinches in parts of the Fennoscandian region (Norway, Sweden, Finland, and Denmark) are synchronized with rowan masting episodes, and the arrival of fieldfare and redwing flocks to Britain is regulated by the onset of winter and the dwindling supply of rowan berries in Scandinavia and continental Europe.

Messy they may be, but the beetles that pollinate rowan flowers have quite an influence on the life of the rowan tree and the birds that feed on its juicy berries.