Category Archives: Butterflies

Pollinator seminar at Westminster – the official version – and that 1,500 figure

Last month I wrote a personal account of the National Pollinator Strategy Seminar held at Westminster. This week the Parliamentary Office for Science and Technology released their official summary of the event plus PDFs of the slides of some of the participants. They can be downloaded from this website. It was an interesting seminar and it’s well worth taking time to study these documents; they are very accessible for the non-specialist.

One thing that’s unclear to me from this account is with regard to the statement that: “there are approximately 1,500 insect species that pollinate food crops and wild plants, including bees, hoverflies, wasps, flies, butterflies, beetles and moths”. The National Pollinator Strategy also cites that figure, though says “at least 1,500” species.

Where does the 1,500 figure come from? Does anyone know the original citation? I genuinely can’t recall if I’ve ever seen it published.

A quick back of the envelope, conservative calculation suggests to me that 1,500 species is too low:

Aculeates (bees plus wasps minus ants) =	500
Butterflies =	59
Macro-moths (assumed 50% flower visitors) =	400
Hoverflies =	250
Other flies (assumed 10% flower visitors) =	700
Beetles (assumed 5% flower visitors) =	200
Total species =	2109

Links are included to the sources of the original diversity figures. I’ve rounded some of the figures down and the % flowers visitors figures for moths, flies and beetles is pure guestimate based on my field experience. But they are not likely to be way out, and if anything could be an under-estimate for flies and beetles; moths could be too high, though most species do feed as adults. Aculeate Hymenoptera (bees and wasps) could also be an over-estimate, but then that figure doesn’t include the non-aculeate “wasps” that frequently visit flowers, for example many ichneumonids and sawflies.

Does it matter? I think so: as scientists it’s important that we provide the most accurate data that we can to governments and other bodies that may use it for policy, strategy and advocacy.

As always I’d be pleased to receive your comments.

Urban pollinators for urban agriculture (and horticulture!)

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Over the past few weeks I’ve been thinking a lot about urban pollinators, that is to say bees, hoverflies, butterflies, and other animals, living and foraging in towns and cities. As I recounted in my recent post about the National Pollinator Strategy seminar at Westminster, Jane Memmott presented some of the first data from the Urban Pollinators Initiative which is looking very interesting. At the same time, Muzafar Hussain has submitted the first manuscript from his PhD study of urban solitary bees in Northampton, and will hopefully be defending his thesis early next year. More recently I was asked to examine the PhD thesis of Rob Fowler at the University of Birmingham, whose focus has been on pollinators across an urban-rural gradient. Rob did very well and I look forward to seeing his work published.

Interesting though all this work is, it’s largely being done outside the context of crop pollination per se, focusing mainly on the identity and abundance of these urban pollinators. It’s timely, therefore that a study has just been published by Thebo et al. in the journal Environmental Research Letters entitled “Global assessment of urban and peri-urban agriculture: irrigated and rainfed croplands” which gives the first comprehensive figures on the extent of agriculture in and around the world’s large towns and cities. The paper is open-access so you can read its findings for yourself, but the main message is that urban agriculture is more extensive and important than previously assumed, and there are significant implications for food security and water resources.

The research has (justifiably) received quite a lot of publicity in the media, for example on the BBC News website, and is a great contribution to a still limited field of study. One aspect jumped out at me though; when discussing the limitations of their methods the authors state that: “the scale and methods used……are not structured to capture very small, spatially dispersed areas of urban croplands”. In other words, urban gardens and allotments are not included in this assessment. In the UK at least this is a significant limitation as we know that urban fruit and vegetable growing is widespread, though as far as I’m aware there’s no published figures on the volume and value of this local horticulture of food crops.

Which brings us back to urban pollinators: a significant fraction of these crops (large-scale and local garden) requires pollination by insects. As I reported back in July, in our own urban garden this includes at least 15 crops (strawberries, apples, greengages, cherries, blackcurrants, squashes, courgettes, blackberries, fennel, runner beans, french beans, passion fruit, tomatoes, raspberries, and radish pods). An integrated study of urban agriculture/horticulture in the context of pollinator diversity and abundance would be a great piece of research and is long overdue.

The National Pollinator Strategy – some reflections

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After many months of consultation and workshops, the National Pollinator Strategy for England has finally been released by Defra, and can be downloaded from this website. It reflects an important, wider change in societal attitudes to nature, and specifically the ecosystem services it provides, though the strategy itself is by no means perfect. I rather wish that it had been a UK-wide strategy, as biodiversity does not respect political boundaries, but such is a the nature of our partly-devolved political system. Wales already has an Action Plan for Pollinators and I hope that the rest of the UK follows, though a strategy for Northern Ireland would surely have to include the Republic of Ireland?

In the following sections I’ve quoted liberally from the summary section of the National Pollinator Strategy, and added a few comments and reflections of my own in italics. As always, your views and comments would be very welcome.

The 10 year National Pollinator Strategy aims to deliver across five key areas:

1. Supporting pollinators on farmland

Working with farmers to support pollinators through the Common Agricultural Policy and with voluntary initiatives to provide food, shelter and nesting sites.
Minimising the risks for pollinators associated with the use of pesticides through best practice, including Integrated Pest Management (IPM).

Comment: at the moment many farmers are already pro-actively encouraging pollinators and other wildlife, but most are not. Will “voluntary initiatives“, including encouraging Integrated Pest Management, be sufficient? About 70% of the country is farmed and any wildlife conservation strategy has got to include agricultural stakeholders. But the influence of large agro-chemical businesses should not be under-estimated. I’ve seen figures suggesting that fields of oil seed rape in this country receive applications of up to 20 different chemicals (biocides and fertilisers) each year. That represents a significant profit for these companies, who will not want to change the status quo. Data showing a slow down in the rate of decline of plants and pollinators in Great Britain, the Netherlands and Belgium may be evidence that CAP agri-environmental schemes have had a positive impact, but I’d like to see more data addressing that question (and not just for pollinators – farmland birds are doing worse than any other category of birds in the UK).

2. Supporting pollinators across towns, cities and the countryside

Working with large-scale landowners, and their advisers, contractors and facility managers, to promote simple changes to land management to provide food, shelter and nest sites.
Ensuring good practice to help pollinators through initiatives with a wide range of organisations and professional networks including managers of public and amenity spaces, utility and transport companies, brownfield site managers, local authorities, developers and planners
Encouraging the public to take action in their gardens, allotments, window boxes and balconies to make them pollinator-friendly or through other opportunities such as community gardening and volunteering on nature reserves.

Comment: “simple changes to land management” can do a lot for supporting local biodiversity, even in the most unlikely, urban settings, which is the underlying philosophy behind our award-winning Biodiversity Index tool. Quite a number of local authorities are getting the message that it’s A Good Thing to reduce the frequency of cutting amenity grasslands, both for pollinators and for budgets. But local authorities are also taking foolish decisions with regard to developing sites that should be protected, and brownfield areas are being specifically targeted for building urban housing, despite the fact that we have long known that they are some of our best sites for pollinators. How do we reconcile these different priorities? Brownfield sites by their nature are transitory, early successional habitats, so perhaps local authorities should be encouraged (made?) to have a rolling stock of a minimum proportion of undeveloped brownfield sites as part of their portfolio of land holdings? Or how about a requirement that all developed areas of brownfield land are replaced by an equivalent area of brown roofs?

3. Enhancing the response to pest and disease risks

Working to address pest and disease risks to honey bees whilst further improving beekeepers’ husbandry and management practices to strengthen the resilience of bee colonies.
Keeping under active review any evidence of pest and disease risks associated with commercially produced pollinators used for high-value crop production.

Comment: interestingly there’s no mention of disease risks to non-managed pollinators, yet we know that honey bee diseases can be passed to bumblebees, for instance.

Actions to support these priority areas:

4. Raising awareness of what pollinators need to survive and thrive

Developing and disseminating further advice to a wide range of land owners, managers and gardeners as part of Bees’ Needs.
Improving the sharing of knowledge and evidence between scientists, conservation practitioners and non-government organisations (NGOs) to ensure that actions taken to support pollinators are based on up-to-date evidence.

Comment: yes, dissemination of sound, evidence-based knowledge has got to be a priority.

5. Improving evidence on the status of pollinators and the service they provide

Developing a sustainable long-term monitoring programme so we better understand their status, the causes of any declines and where our actions will have most effect.
Improving our understanding of the value and benefits pollinators provide, and how resilient natural and agricultural systems are to changes in their populations.

Comment: monitoring of pollinators is a real sticking point in the strategy, as there’s still no consensus on what should be monitored, how, where, and how frequently. This was the subject of a workshop at the Natural History Museum in London that I attended about a year ago, and there’s still much that is undecided. I know that a partnership led by CEH Wallingford is working on this at the moment, and hopefully a scheme will be in place by next year. Let’s see what they come up with.

In taking action across these five areas, the National Pollinator Strategy wants to achieve the following outcomes:

More, bigger, better, joined-up, diverse and high-quality flower-rich habitats (including nesting places and shelter) supporting our pollinators across the country.
Healthy bees and other pollinators which are more resilient to climate change and severe weather events.
No further extinctions of known threatened pollinator species.
Enhanced awareness across a wide range of businesses, other organisations and the public of the essential needs of pollinators.
Evidence of actions taken to support pollinators.

Comment: “More, bigger, better, joined up…” has been the buzz phrase in British conservation since at least the Lawton Report. One of the outcomes of that report was the setting up of twelve flagship Nature Improvement Areas (NIAs), one of which is the Nene Valley NIA, a project on which my research group has been working. The Strategy mentions the NIAs several times and states that “extending the monitoring and evaluation framework for Nature Improvement Areas to include pollinators” is one of its interim aims. But as I recently mentioned, funding for the NIAs finishes at the end of March 2015 and Defra has indicated that there will be no additional government money. How will this aim be met? I’d be very interested to know as the Nene Valley NIA is one of the few which specifically focused on pollinators as part of our remit. It would be a terrible shame to lose the expertise and momentum that we’ve built up when funding stops next year. As regards “No further extinctions of known threatened pollinator species“, the talk I gave at SCAPE 2014 was on that very topic and a paper outlining our results is currently in press. I hope to be able to share those findings with the broad readership of this blog very shortly.

Gatekeeper in the garden

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Since moving into our house in January 2012 I’ve been keeping a list of butterflies and day-flying moths seen in the garden (as well as birds and bees, of course). That list currently contains 14 species*, one of the most interesting of which is the Gatekeeper (Pyronia tithonus).

According to the account of this species on the UK Butterflies web site, the Gatekeeper:

“can be found wherever shrubs grow close to rough grassland. ……some of the largest colonies can be found at field edges and along hedgerows and we can expect to find this butterfly in scrubby grassland, woodland rides, country lanes, hedgerows and the like anywhere within its range”.

So what is it doing in an urban garden? The BTO’s summary of the species mentions that:

“It is rare for Gatekeepers to appear in city-centre gardens. However, in recent years this species has been recorded at some urban sites across north-east London and Hampstead Heath and, more recently, on Wimbledon and Mitcham Commons. Such range expansion into urban areas may be due in part to changes in the management of urban parks and cemeteries”.

Clearly, in order to exist in an urban setting the Gatekeeper must have its basic requirements met by the habitat in which it finds itself. As I’ve mentioned before, the lawn in our garden is quite diverse and contains a number of native species, including a range of grasses that could be used as food plants by the caterpillars, though we do keep it quite short. It’s more likely that the caterpillars are feeding in some of our neighbouring gardens, which are rarely troubled by a mower (do neglected gardens host more biodiversity than highly managed gardens? I suppose it depends on the type of management; would be an interesting question to research).

As well as the larval food plants required by Gatekeepers, there’s a range of nectar sources available in a mixed native/introduced hedge along the northwest boundary, including the bramble I recently discussed, oval-leafed privet (Ligustrum ovalifolium), and the buddleia (Buddleja davidii var.) seen in these photographs.

It will be interesting to see if this colony persists over time (I also recorded the species in 2013 but not in 2012). I get the impression that there’s only a small number of individuals, though it’s difficult to assess the population size of butterflies without catching and marking individuals, which I plan to do next year. It’s a lovely species and we’re fortunate that it likes our garden. I’d be very interested to hear from any other urban gardeners who have seen it in their patch.

*Large White, Speckled Wood, Small White, Holly Blue, Red Admiral, Cinnabar, Large Skipper, Meadow Brown, Peacock, Gatekeeper, Comma, Brimstone, Orange Tip, Small Tortoiseshell.

All pollinators are equal, but some pollinators are more equal than others

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The infamous line from George Orwell’s Animal Farm asserting that “All animals are equal, but some animals are more equal than others” nicely captures an ecological view of pollinators and their relationships with plants. “Pollinators” by definition move pollen between flowers, but not all pollinators are equally good at transferring pollen of any particular plant: some are more effective than others. I’ll illustrate this with examples from the urban garden that Karin and I are developing, which I’ve discussed before.

As you can see from that link, the garden is modest in size, but nonetheless this year it contains a significant biodiversity of edible plants that require pollinators for some or all of the fruit and seed set, including: strawberries, apples, greengages, cherries, blackcurrants, squashes, courgettes, blackberries, fennel, runner beans, french beans, passion fruit, tomatoes, raspberries, and radishes.

“Radishes?!” I hear you ask. “But they are grown for their edible swollen roots which don’t require pollination!” True, usually. But we let our radishes flower because we mainly grow them for their seed pods which, picked young, are delicious in salads and stir fries, like mustardy mange tout. They look like this:

The radish flowers are pollinated by a diversity of insects including butterflies, bees, and small flies:

These insects will vary in their effectiveness as pollinators of radish, depending on the frequency of visits, how often they move between flowers, and the amount of pollen on their bodies. This last factor is largely a function of size and hairiness (bigger, hairier insects carry more pollen as a rule), though cleanliness also plays a part: insects often groom the pollen from their bodies and, in the case of bees, may pack it into their pollen baskets where it’s not available for pollination.

The size and behaviour aspect is best illustrated by some recent photos that I took of visitors to the flowers of passion fruit (Passiflora caerulea var.). We have a large, sprawling plant growing up a fence which is currently being visited by honey bees, hoverflies, solitary bees and bumblebees. In comparison to the size of the flower and the position of the anthers (male, pollen producing parts) and stigmas (female, pollen receiving parts), the hoverflies, honey bees and solitary bees are relatively small. These two images are of honey bees (Apis mellifera):

Here’s an unidentified solitary bee:

These bees were occasionally touching the anthers, mainly with their wings, so some pollen will be moved around. But from what I observed it’s likely to be a relatively small amount in comparison to bumblebees, which are usually much larger and hairier, and don’t groom themselves as often as honey bees. Here’s a Buff-tailed bumblebee (Bombus terrestris):

They were actively collecting pollen as well as nectar. Much of this pollen is packed into the pollen baskets on the rear legs and will go back to the nest to feed the developing larvae, but some will be involved in pollination:

So it seems to be the bumblebees we have to mainly thank for the deliciously sweet-sour fruit we will enjoy later in the season. Of course to test this properly we would need to set up an experiment in which we excluded larger bumblebees from the flowers and only allowed smaller bees to forage, with appropriate experimental controls. Would make a great project if any of my students are interested! But it should give you a sense of just how complex the interactions between flowers and their pollinators are: the ecology of pollination is far from simple, despite what some would have us believe.