Nectar from urban gardens to the rescue of insects

A sunny spring day in the Deux-Sèvres. In my garden, bees and bumblebees are buzzing. Just on the other side of the dry stone wall, the agricultural plot is silent. Populations of pollinating insects are collapsing in Western Europe, mainly due to lack of food. Are populated areas refuges for all the little beasts?

Colleagues (1) investigated this question in 12 locations in the UK, comparing the amount of nectar produced by flowers in cities, agricultural areas and protected areas. To do this, they collected as much nectar as possible from the different flowers with a micropipette, becoming foragers themselves.  To their great surprise, there was on average no more nectar available for insects in the city than in agricultural areas and protected areas. However, within urban areas, some fully concreted habitats were extremely poor, while home gardens produced 85% of all available nectar, four times more than public parks. Thus, insects have much more food available to them in a garden than on an agricultural area. This urban nectar comes from a wide variety of plants, which contributes to its quality and extends the period of the year during which it is available. The second surprise was that 83% of the nectar in the gardens was produced by exotic plants. These species are often considered to be “beautiful and useless”, as they do little to benefit local biodiversity. Some are even invasive and potentially harmful. In fact, the study by British academics indicates that exotic flowering plants may have become essential for the survival of insects in our urban landscapes. Of the 536 flowering plants they studied, the scientists point out that species such as borage and butterfly tree (from the Middle East and China respectively) are excellent sources of nectar. For public parks, they recommend reserving certain areas to grow mixed flowers, which produce 16 times more nectar than a lawn.

This study is sure to delight urban gardeners, where flowering plants are now taking on a militant air; I’ll be thinking of them as I watch the bees foraging in the borage beds that bloom on the edge of my vegetable garden.

(1) Tew, N. E., Memmott, J., Vaughan, I. P., Bird, S., Stone, G. N., Potts, S. G., & Baldock, K. C. (2021). Quantifying nectar production by flowering plants in urban and rural landscapes. Journal of Ecology 109: 1747-1757.

Bombus pascuorum (Photo credit: Getty)

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