Sprawling urban development is responsible for high rates of biodiversity declines but in the midst of a pollinator crisis, bees are thriving in our cities. If managed correctly (which might be surprisingly easy), cities can potentially play an important role in reversing the rampant decline we are seeing in bee populations: one of our most economically valuable, ecologically important and threatened animal groups. However, city planners are struggling to take scientists’ advice.
The buzz kill
City dwellers and countryside folks alike, few can have missed that our bees are in decline. Say what you will about media coverage (or lack thereof) when it comes to conservation issues that are threatening global biodiversity, but the public have been made well aware of our dying striped friends. If you’ve forgotten why, bee sure to have a look at Figure 1 and this video.
Cities: the bees knees
When scientists compared the number of bee species in farmland areas, nature reserves and twelve cities across the UK, they found the cities to be the most species rich1. The scientists behind the nationwide study reasoned that cities offer a smorgasbord of both food and nesting sites compared to their more rural counterparts. Food is plentiful and varied, as cities have both native and introduced plant species. Similarly, the urban housing market for nifty bees is incredibly diverse, including cavities in walls and other man-made structures.
However, it is worth noting that the same study1 also found that hoverflies (which like bees, are important pollinators) did worse in cities. As such, we cannot fully rely on concrete jungles to reverse pollinator declines, conservation in both cities and undeveloped lands is vital.
Michelin star buffet for big city bees?
The city as a refuge for bees poses an important question: can we manage our metropolises to make them even better suited to host our declining populations? The answer is yes, and it might be easier than we thought. If you’ve ever been to a garden center on the hunt for seed mixes, you’ll know that many claim to be “pollinator friendly”. They’re probably lying. The truth is that until recently we knew very little about bees’ palates. Bees need flowers that produce both nectar and pollen throughout the season, which normally lasts from April to September in the UK. Unfortunately, there is no super-flower that provides bees with everything they need all the time, but by planting a carefully selected mix of flowers that together do just that, we can help our busy bees out (Figure 2).
A group of British researchers recently compared the nectar and pollen content in over two million flowers from 65 different flower species, as well as when the flowers released their nectar and pollen2. The results varied a lot between species with some of our most beloved garden species acting as the worst for pollinators whilst dreaded weeds like dandelions were among the best (Figure 3). This is good news for the lazy urban garden owner: by simply not removing some weeds, you can help to save our bees! The researchers hope that their findings will inform city planners about what species to plant in public green spaces.
“ATTENTION all urban garden owners: be lazy!”
Another study used citizen science to understand flower preferences in the UK’s seven most common bumblebee species in gardens and allotments3. It revealed that most of the time nature’s busy bumblebees only bothered to visit about 10% of available flower species. However, different bumblebee species had slightly varied flower species preferences. Other studies have found that bee and flower species diversity often go hand in hand4, so there is no point excluding everything that isn’t a highflyer in terms of nectar and pollen production.
Buzzing city bees equals buzzing… everything?
An additional benefit of increasing our urban bee populations is that eventually they could become so numerous that they repopulate surrounding landscape types by what is called a spillover effect. Scientists cannot definitively say that a spill over effect will happen but it is far from unlikely4. Now for the big surprise: flowers in cities make people happy2,4! We still have a lot to learn about what make urban environments good for bees but carefully planned inner-city flower meadows are definitely a double win (Figure 4)!
Urban conservation programs are lagging beehind
Although governments worldwide are putting bee conservation programs into action, urban initiatives are not often based on sound evidence4. Garden rooftops have become an appreciated feature of many major cities in recent years, but without planting the right species to cater to a bee’s palate (as recommended by the study mentioned above), we are not making the most of these special urban bee havens.
Even worse, attempts to make cities bee-friendly could sting. Many have probably heard about bee hotels, which are man-made nest sites made from hollow tubes stacked together, built to provide five star residences for solitary bees. Even the RSPB has encouraged Britons to install these but Canadian researchers have shown that at least in Toronto, they host more undesirable bee and wasp species than native bee species and as in any crammed flat share, they can make the spread of parasites easier5. This is not to say that bee hotels are a total buzz kill, but they need to be well maintained, and constructed with the size of native bees in mind.
To conclude, although we still have a lot to learn about what makes cities the bees’ knees, urban bee conservation is a buzzing field that puts high-impact urban conservation within reach. It is not only bees that prefer the big city life, about two thirds of the global population are estimated to be living in cities by 2050 and much of these urban areas are yet to be built. By implementing what we already know and contributing to drive research, we can hope to build smarter and more suitable cities to accommodate human and bee populations alike for generations.
1 Baldock, K. C. R., Goddard, M. A., Hicks, D. M., Kunin, W. E., Mitschunas, N., Osgathorpe, L. M., Potts, S. G., Robertson, K. M., Scott, A. V., Stone, G. N., Vaughan, I. P. and Memmott, J. 2015. Where is the UK’s pollinator biodiversity? The importance of urban areas for flower visiting insects. Proceedings of the Royal Society B Biological Sciences 282 1803 : 20142849.
2 Hicks, D. M., Ouvrard, P., Baldock, K. C. R., Baude, M., Goddard, M. A., Kunin, W. E., Mitschunas, N., Memmott, J., Morse, H., Nikolitsi, M., Osgathorpe, L. M., Potts, S. G., Robertson, K. M., Scott, A. V., Sinclair, F., Westbury, D. B. and Stone, G. N. 2016. Food for Pollinators: Quantifying the Nectar and Pollen Resources of Urban Flower Meadows. PLoS ONE 11(6): e0158117.
3 Foster, G., Bennett, J. and Sparks, T. 2017. An assessment of bumblebee (Bombus spp) land use and floral preference in UK gardens and allotments cultivated for food. Urban Ecosystems 20: 425-434.
4 Hall, D. M., Camilo, G. R., Tonietto, R. K., Ollerton, J., Ahrné, K., Arduser, M., Ascher, J. S:, Baldock, K. C. R., Fowler, R., Frankie, G., Goulson, D., Gunnarsson, B., Hanley, M. E., Jackson, J. I., Langellotto, G., Lowenstein, D., Minor, E. S., Philpott, S. M., Potts, S. G., Sirohi, M. H., Spevak, E. M., Stone, G. N. and Threlfall, C. G. 2016. The city as a refuge for insect pollinators. Conservation Biology 31: 24-29.
5 MacIvor, J. S., Packer, L. 2015. ‘Bee Hotels’ as Tools for Native Pollinator Conservation: A Premature Verdict? PLoS ONE 10(3): e0122126.