Does Toronto Need More Wild Bees?



Does Toronto Need More Wild Bees?

Why a York University PhD student thinks there's a place for bees in urban planning and landscape design.

Although you can’t see it from the sidewalk, there’s a condo atop the University of Toronto’s Faculty of Architecture building at 230 College Street. Far from being another of those soulless glass boxes scattered around the city’s downtown, however, this condo is all about life and diversity. But it’s bees and wasps only, here.

What most people would call a nest box, York University doctoral candidate Scott MacIvor likes to call a “bee condo.” It’s MacIvor who placed the footlong bee home on the roof of the architecture building, where U of T maintains its Green Roof Innovation Testing Laboratory, or GRIT Lab.

The nest box is just one of many MacIvor has placed around the city. He’s hitched them onto everything from trees in quiet ravines to stop signs downtown, as part of a four-year experiment on wild-bee diversity in Toronto that is now in its final year.

“There’s been a flurry of research in the last decade or so suggesting that urban landscapes have a negative impact on wild species in general,” MacIvor says. Yet some species, like pigeons and certain weeds, seem pre-adapted to urban life, and have not only persisted, but flourished in manmade surroundings. MacIvor says this is true of some of Toronto’s 100-plus species of wild bee, too.

“Cities can act as a filter for biodiversity,” MacIvor says. “Going increasingly outside the city, you find more diversity.” He wants to see which wild bees are being filtered out of Toronto’s urban landscape, and which are adapting to it. Already, he’s found that the alfalfa leafcutter bee, for example, is thriving in Toronto, as it’s capable of living nearly anywhere, from rusty nail holes to mailboxes to barbecues. The rusty patch bumblebee, meanwhile, is struggling. MacIvor says he and a labmate have been searching for this bumblebee—which, only about 15 years ago, was one of the area’s most common bees—for two years, and have yet to find one. MacIvor now believes the species to be extinct.

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The GRIT Lab at U of T is home to one of MacIvor’s “bee condos.”

To carry out his project, MacIvor puts up dozens of nest boxes each April. The boxes are made by MacIvor himself. Each one consists of a short length of PVC piping stuffed with foam, into which a number of cardboard tubes are inserted. It’s in these tubes that female bees nest and lay their eggs. The openings of the tubes vary in size—MacIvor explains that bees like to fit snugly into their nests, and, given that different species of bees grow to different sizes, using only one size of cardboard tube (as is common with commercially available nest boxes) could potentially limit the diversity of bees capable of nesting there. Each nest box is fitted with an electronic sensor that allows MacIvor to track environmental variables, like humidity and ambient temperature, which might affect the diversity and number of bees that choose to nest in a given box.

MacIvor takes the nest boxes down in October. He removes and unravels every cardboard tube, documenting meticulously the contents of each one. Each bee larva is put in its own cell, which is then labelled and placed in a refrigerator for a few months, to simulate winter conditions (the larvae don’t freeze—evolution has gifted them with a natural antifreeze that allows them to supercool the liquid inside their bodies). Finally, in the spring, MacIvor rears the bees in a growth chamber.

MacIvor says the information he gathers will help him to determine “what in urban landscape design dictates the presence or absence of bees and bee diversity.” His research may even reveal ways in which urban landscape design principles could be adapted to enhance wild bee diversity in Toronto.

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One of MacIvor’s nest boxes.

But what makes the humble bee worthy of such efforts?

Wild bees perform an invaluable function in our urban ecosystem: they pollinate many of our myriad tree, flower, and plant species. According to MacIvor, a diversity of bee species performing the same function—that is, capable of pollinating the same species of flora—is beneficial, because it means that if a disturbance in the ecosystem were to eradicate one species of bee, there would likely be several other species capable of carrying out its function, thus ensuring the propagation of the plant species it once pollinated.

Moreover, some species of wild bee are specially adapted to pollinate particular species of flowers that other bees are unable to pollinate. If those specially-adapted species can’t tough it out in the urban environment, their co-evolved counterparts may not be able to either.

(MacIvor also notes the importance of wasps—the other tenants of his bee condos—as “pest-controlling agents,” although he is more interested in the pollination services bees provide.)

While MacIvor says bee diversity (and biodiversity, generally) is important and worth protecting in its own right, he adds, “What’s interesting is putting an anthropocentric spin on ecosystem functions and referring to them as ecosystem services. So in that way we can start to tell people that we are a part of biodiversity as humans as well, and we can derive benefits from there being a breadth of species doing the same thing.”

There are aesthetic benefits, of course. “Even green space in cities will become significantly homogenized to only those that are wind-pollinating, like dandelions, grass, willow, oak, and maple, if we don’t have pollination services,” MacIvor says.

But there may also be economic advantages to having a diverse wild-bee assemblage in Toronto. Current urban landscape design practices mean that when a flower or plant in a human-maintained garden dies, it’s simply replaced. “It’s interesting to me,” MacIvor says, “how landscape architecture and design, unwittingly, could potentially make bees and pollination redundant in some cases.” But, he adds, if the urban landscape were designed in such a way that more wild bee species were allowed to flourish, those bees could aid in the maintenance of garden plants and flowers, potentially reducing the cost of maintaining them ourselves.

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The face of one of MacIvor’s nest boxes, with its electronic sensor visible to the left.

MacIvor says bees need three things: pollen and nectar, both of which are abundant in Toronto; nesting material—some bees collect leaves and mud, while others will use anything from flower petals to plastic bags; and places to nest. According to MacIvor, when it comes to bee diversity, “nest locations are the limiting factor for a lot of these bees.” He says around 80 per cent of Toronto’s bee population nests in the ground. “So there’s a limiting factor right there, if we’re paving everything.”

During the first three years of his project, MacIvor has learned much. He’s found, for example, that bee colonization of green roofs decreases significantly with building height. After four or five storeys, he says, colonization drops, and so does diversity.

There’s a lot still to learn about bees and green roofs, in fact, especially as the latter become more prevalent in Toronto. Green roofs, MacIvor says, “could be a good thing if the [urban] landscape is so depauperate that there’s not enough forage for [bees] and a green roof enhances foraging opportunities.” But, he adds, green roofs could also have a negative effect on bees if, say, their elevation endangers the lives of bees who are forced to go up and down the sides of buildings to reach their nests.

MacIvor says there are still lots of questions to be answered. But urban landscape design should play a role in enhancing Toronto’s biodiversity, he says, “and without thinking about bees in that equation, we’re shorting ourselves quite a bit.”

Photos by Graeme Bayliss/Torontoist, unless otherwise indicated.