Walk this way

Bumblebee Conservation Trust runs various citizen science projects. One of the finest examples is BeeWalk. The central goal of the BeeWalk programme is to be able to reliably evaluate the trends in British bumblebee populations. 

Bombus terrestris (c) Helen Dickinson

This deceptively simple scheme gets people involved in collecting data so that The Trust can get more get information on exactly which species are faring well and which species are a cause for concern, and how bumblebee populations are changing over time.  

One of the most pleasing outcomes is the way in which the project further raises awareness of bumblebees. The more people come to understand our pollinating insects the more they come to appreciate them and become motivated to take action to help them. That you can contribute data whilst taking some healthy exercise is another bonus.

BeeWalk has been on the go since 2008, and the general public have been able to contribute since 2011 (Bumblebee Conservation Trust members were involved from 2010 following a two-year trial stage).  Volunteer ‘BeeWalkers’ simply walk the same fixed route each month from spring to autumn, starting in March and ending in October. The army of willing walkers count the bumblebees they see, grouping them by species and further separating them into queen, worker, or male categories.

The time frame is designed to cover the period from a queen’s emergence out of overwintering through to nests dying out at the end of the season. 

Of course 2020 saw a blip in data collection. The pandemic meant that some walkers couldn’t visit their transect, some volunteers were shielding, and general Covid-related restrictions impinged on normal practice. However, the scheme bounced back in 2021, and this year has seen normal service more or less resumed.

BeeWalk data enables the Trust to assess the size of bumblebee populations and how these change over time. From this they can closely monitor population trends, which can be used to identify at risk species and direct conservation activities. The year-on-year gathering of data is hugely beneficial as cumulatively it forms the basis of long-term monitoring of bumblebee population changes.

It’s a cliché, but from small steps big things can happen. Individual BeeWalkers will likely return to their gardens and follow pollinator-friendly planting regimes. They may spread the word locally, and with luck influence individuals, communities and local authorities to factor pollinator-friendly practices into their greenspace management practices. 

BeeWalk has gone from strength to strength. Today there are over 600 active BeeWalkers and even in 2020 BeeWalk volunteers were still able to survey over 500 transects. By the end of the 2020 season, across the lifetime of the scheme almost 175,000 BeeWalk records had been submitted and around 558,000 individual bees had been recorded. 

Bombus monticola and Bombus soroeensis (c) Annie Ives / Skills for Bees Scotland project.

Bumblebee Conservation Trust haven’t rested on their laurels however.

Skills for Bees complements the BeeWalk scheme by offering more targeted training and support for bumblebee recorders, in under-recorded areas of Britain. In Scotland this has centred on the Cairngorms, where historically there are comparatively few bumblebee records or indeed BeeWalks. It’s a good choice of focus as several nationally scarce species are known to occur there, including the Bilberry (Bombus monticola), Broken-belted (Bombus soroeensis), and Moss Carder bumblebees (Bombus muscorum). Through training and targeted survey days, the project will be greatly increasing knowledge of bumblebees in the area. Anyone interested in getting involved should contact Project Officer Annie Ives by email @ annie.ives@bumblebeeconservation.org 

With the emergence of hugely popular research and monitoring projects, such as FIT-Counts and BeeWalks, citizen science is both raising awareness and providing valuable data. Long may their success continue.

Notes:

The most recent BeeWalk report was published in 2021.  

If you would like to get involved you can find further information on the BeeWalk website

Find out more about bumblebees at www.bumblebeeconservation.org

With sincere thanks to Helen Dickinson of Bumblebee Conservation Trust for all her help in compiling this article.

Uncouth pollinators

By Athayde Tonhasca

If you were to go shopping for fruit in tropical countries and in Florida (USA), you would have the option to take home some sugar apples (Annona squamosa). This rich, tasty and aromatic fruit is a favourite in the West Indies, and its cultivation has been increasing vigorously in many countries. Perhaps too vigorously: sugar apples have become invasive in some places.

Other related species are also valued as desserts and as food for wildlife, such as the cherimoya (A. cherimola) – which Mark Twain considered ‘the most delicious fruit known to men’ – the araticum (A. coriacea) and the atemoya, which is a hybrid of A. squamosa and A. cherimola.

L: A ripe sugar apple readily breaks apart to reveal segments of pulp-encased seeds © Pouletic; R: An araticum fruit © Etore.Santos, Wikimedia Commons.

These plants, together with more than 90% of species in their family (Annonaceae), have one particularity that sets them apart from the majority of cultivated fruits: they are pollinated by beetles.

As the story goes, J.B.S. Haldane (1892-1964), British/Indian geneticist, evolutionary biologist, mathematician and more, found himself in the company of a group of theologians. On being asked what one could learn about the Creator from studying his creation, Haldane – an atheist – is said to have answered ‘an inordinate fondness for beetles.’ Indeed, a Great Designer would have needed to be partial to the order Coleoptera, which is one of the most diverse groups of animals on Earth. With over 400,000 known species, and certainly a much larger number waiting to be discovered, beetles make up one of the largest biodiversity segments of virtually every terrestrial habitat.

Beetle diversity is believed to be associated with the explosive expansion of flowering plants during the Cretaceous period (145-65 million years ago). A greater variety of plants created more opportunities for beetles and other insects that fed on living plant tissue. The resulting coevolutionary arms race – plants’ chemical and physical defences against herbivores promoted counter-measures from plant-munching beetles – helped the diversification of plants and beetles. So today, about 50% of all herbivorous insects are beetles.

Among those early plant feeders, some specialised in pollen – which is not an easy thing to do because pollen is hard to digest. These pioneer palynivores (pollen eaters) are believed to be the first pollinators. By moving from plant to plant to feed, they became contaminated with pollen, thus enabling plant fertilisation. With time, bees, flies and moths took over the role of main pollinators. But some plants, especially of ancient lineages such as magnolias (Magnoliaceae), retained cantharophily – from the Greek kántharos (beetle) and philos (loving), it means pollination by beetles. The Annonaceae, arums (Araceae), palms (Arecaceae), and orchids (Orchidaceae) are also well represented in this form of pollination.

Beetles have none of the elegance or restraint of a nectar-sipping moth or a pollen-picking bee. They plough through a flower, wolfing down pollen (some eat nectar and petals as well), often spilling more grains than eating them, defecating as they go. That’s why they are called ‘mess and soil‘ pollinators. And they like to hang around. While most insect pollinators stay on a flower just long enough to collect pollen or nectar, beetles usually are in no hurry: they may stay put for hours or days. The flower beetle Carpophilus mutilatus, one of the main pollinators of atemoya, stays inside a flower for up to 22 h.

A scarab beetle helping itself on a California brittlebush flower (Encelia californica) © Marshal Hedin, Creative Commons.

Plants adapted to these uncouth and destructive visitors by producing thick or leathery flower parts and copious amounts of pollen to compensate for losses to consumption and spillage. And they encourage beetles to stay: their flowers usually have sepals and petals curved inwardly to form a pollination chamber, which is a dark, safe and cosy space for beetles to frolic to their heart’s content. But there’s more: most cantharophilous flowers produce strong perfumes, which people have described as spicy, sweet, musky, or as reminiscent of overripe fruit – thus irresistible to some beetles. A number of these flowers are also thermogenic – they produce heat – when they open and become functional (the anthesis period). A warm flower disperses its scents with ease and welcomes beetles fleeing the cold.

The flower of soursop (Annona muricata) © Ton Rulkens, Wikimedia Commons.

Most cantharophilous plants would not win a prize in a flower show, but never mind our aesthetic preferences; their objective is to reward the creatures that help them reproduce. Sap beetles (Nitidulidae), long-horned beetles (Cerambycidae), leaf beetles (Chrysomelidae), rove beetles (Staphylinidae), scarabs (Scarabeidae), tumbling flower beetles (Mordellidae), click beetles (Elateridae), blister beetles (Meloidae) and weevils (Curculionidae) are welcomed with a place to feed, mate, and shelter from the weather and predators. Many of these visitors are hairy, so with luck, some pollen grains get attached to their bodies and transported to another flower.

L: Flower of Annona coriacea with the external petal removed to reveal a Cyclocephala ohausiana feeding on the floral chamber; R: C. atricapilla with pollen attached to their bodies © Costa et al. 2017. PLOS ONE 12(2): e0171092.

Plants that rely on beetles for pollination are more common in tropical-Mediterranean regions, and in semi-desertic areas, such as South Africa and southern California. But temperate regions have their share of cantharophilous species such as the rowan tree (Sorbus aucuparia) water lilies (Nymphaeaceae) and goldenrod (Solidago spp.). Considering the number of beetle species out there, and the likely much greater number yet to be described, the list of cantharophilous plants is bound to increase as we learn more about these unsophisticated ‘mess and soil’ flower visitors.

A flower Beetle visiting the Jardin Botanique de Montréal. © Ewok Slayer, Wikimedia Commons.

Helping hands

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

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

Lennoxtown Meadows

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

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

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

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

Enjoying Stonefield Park, Blantyre

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

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

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

Elder Park, Glasgow

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

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

Silverknowes Park meadow

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

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

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

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

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

Ruchill Park, November 2021

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

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

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

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