Flowering in the city: the bumblebee connection

By UdeMnouvelles Apr 20th, 2026

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In 5 seconds The flowers of the Spotted Jewelweed (Impatiens capensis) are larger in cities. This appears to be an adaptation to the size of its primary pollinator, the Common Eastern Bumblebee.

Jewelweed flowers are generally larger in urban areas.
Photo : Simon Joly

Why are flowers so different from one another?

Much of the answer lies with pollinators: their preferences and morphologies have helped generate an exceptional diversity of flowers in terms of shape, size, color and scent, forcing them to adapt so they can reproduce effectively.

But as the human population grows across the planet, prairies and wetlands are being destroyed and replaced by urban landscapes of impermeable surfaces — and that's a problem for flowers and their pollinators.

While some organisms, such as rats or cockroaches, successfully conquer urban environments, others — like pollinators — show more nuanced responses to urbanization. Some species tolerate or adapt, while others perish, leading to significant shifts within biological communities.

Since pollinators in cities often differ from those in natural settings, a question arises: do plants, through their flowers, show they're adapting to these changes?

Jérôme Burkiewicz, a PhD candidate in biological sciences at Université de Montréal, went to find out.

In a study supervised by UdeM biology professor Simon Joly, a researcher at the Montreal Botanical Garden, Burkiewicz shows that flowers of the Spotted Jewelweed (Impatiens capensis) do indeed adjust to the changes induced by urbanization on pollinators.

Different bumblebees in the city

Studying several populations of Jewelweed in the Toronto, Ottawa, Montreal and Quebec City areas over a two-year period, the scientists observed that although bees, flies, wasps and hummingbirds pollinate the plant, bumblebees are clearly the primary pollinators.

However, while the Half-black Bumblebee (Bombus vagans) typically pollinates Jewelweed in natural settings, the Common Eastern Bumblebee (Bombus impatiens) more frequently takes on this task in urban environments.

Another key difference: the bumblebees were larger in the city than in natural habitats.

After making these observations, the researchers grew plants from seeds they'd collected in the field to study them in a controlled environment. They found that flower size within a population correlates with the size of the pollinators: the larger the bumblebees, the larger the flowers.

Consequently, Jewelweed flowers are generally larger in urban areas.

"To extract nectar from a Jewelweed flower, bumblebees must enter the flower and, in doing so, touch the reproductive parts and pollinate the plant," explained Burkiewicz.

"If the flowers are too small, the bumblebees might not be able to enter; if they are too large, they might enter without pollinating the plant. This could explain the correlation between the size of the flowers and that of the pollinators."

Over 1,900 flowers and 700 pollinators

In all, the researchers photographed over 1,900 flowers, collected approximately 700 pollinators, and observed the pollination of Spotted Jewelweed for 120 hours.

The data collected in the field were compared with data from plants grown under controlled conditions to isolate the genetic effect (permanent change caused by evolution) from the plastic effect (temporary change in response to the environment).

"Pollinators are rarely studied at the same time as plants, and few studies isolate the role of evolution from that of the environment," said Burkiewicz.

"This approach proved essential in demonstrating the link between flower size and pollinator size, but it also showed that the environment triggers significant changes in flowers that are not genetic."

While more and more scientists are investigating the effect of urbanization on pollinators, little research has evaluated the impact on plants. The loss of pollinators could, Burkiewicz said, lead plants to turn toward self-fertilization.

That's certainly an effective strategy for survival, but it reduces genetic diversity and, consequently, the ability to adapt to future environmental changes, he warned.

But at the same time, these results also show that flowers are capable of evolving rapidly to adapt to changes within pollinator communities. So, they may well have more than one trick up their sleeve!