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27/08/2019

Planners can help solitary bees to survive in our urban ecosystems

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Leafcutter bee in purpose made nesting hole

Lesser known and smaller than their charismatic cousins, the solitary bees need our help, says ecologist Rob Evans - and, as planners, you can provide it

Most of us are aware of large, furry bumblebees that live socially in hives with workers supporting a queen. However, there are approximately 270 species of bee in Britain of which only 25 belong to the genus Bombus or bumblebee. More than 90 per cent of our native bee species consist of solitary bees – smaller and less conspicuous than their sociable cousins. 

What’s special about solitary bees? 

Solitary bees are important pollinators; they gather nectar and pollen to provision their nests with food. Unlike honeybees, solitary bees produce neither honey nor beeswax and live alone. A single female creates her own tubular nest, segmented into five to ten individual cells, each containing a single egg. The most common solitary bees in Britain are the various mining bees, which burrow into the soil to make their nests. Other species build their nests in the stems of plants, or even empty snail shells, such as the mason bee (Osmia bicolor)

By foraging for food, bees transport pollen and facilitate pollination. Solitary bee species have adapted to feed on a wide range of plants, from generalist species collecting pollen and nectar from many plant species to more specialist species focusing on a small number of plants and a few entirely dependent on a single plant species, such as the yellow-loosestrife bee (Macropis europaea).

"Solitary bees have suffered worrying losses in diversity, abundance and range. A third of wild pollinator species decreased between 1980 and 2013"

In the UK, solitary bees have suffered worrying losses in diversity, abundance and range. A third of wild pollinator species decreased between 1980 and 2013, according to a recent study by Gary Powney et al (1). With 75 per cent of crop species and 88 per cent of flowering plant species dependent on insect pollination, these declines in our most diverse group of pollinators are a major concern; the canary in the mine shaft is looking peaky. Key threats include agricultural intensification, pesticides, climate change and habitat loss.

Providing shelter for solitary bees

The expansion of urban environments has significantly contributed to the loss and fragmentation of important habitat. However, there is opportunity within these areas to help solitary bees. In contrast to the intensively farmed, homogenous modern agricultural landscapes, the urban ecosystem is varied and valuable for wildlife. With considered planning of our conurbations, it’s possible to soften the urban matrix for bees by providing vital stepping-stones aiding their migration through the local landscape and offering additional foraging resources throughout the year. Both are key in promoting a solitary bee community better equipped to resist pressures, such as climate change and invasive species. 

Solitary bees have been shown to forage at restricted ranges from their nest sites and suitable foraging habitat at 150-600 metres is vital. The diversity of solitary bees is mirrored in their requirements, but an urban environment that is planned to integrate wildflower verges, gardens, scrub, hedgerows, and brownfield sites provides an array of resources. 

Neglected brownfield sites are a paradise for wildlife. Yet they are confronted with a constant battle to be tidied up. Weeds such as ivy, nettle and elder, earth and rubble banks and sprawling bramble scrub provide shelter and foraging habitats.  Neat monocultured hedgerows, non-native yet aesthetically pleasing plantings, billiard table length lawns in urban parks have contributed to the decline in our solitary bees. Some of the most bee-friendly features in urban ecosystems are, unfortunately, viewed as unsightly. Changing opinions by celebrating the diversity of the solitary bee and raising awareness that dishevelled urban patches can help these threatened species will allow a more pragmatic approach to achieving functional towns and cities for our undervalued wild bees.

Rob Evans is assistant ecologist at Pro Vision planning, architecture and urban design consultancy 

1) G Powney et al, Widespread losses of pollinating insects in Britain, Nature Communications 10, article number 1018 (2019) 

Photos | Simon Wicks

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