Turns out Toronto’s bees are better adapted for city living than we thought — and that could be good news for our plants and vegetables.
A new study led by a York University doctoral student shows that wild bees have been incorporating the detritus of urban life — plastic from shopping bags and building materials — into their nests.
“I didn’t really believe it at first,” said Scott MacIvor, whose report was published in Ecosphere journal at the end of December. “There had been anecdotal evidence of bees using plastics in their nests, but it had never been reported.”
Unlike honey bees, wild bee species use plant material to build nests for their young. They build a long strip of “cells,” one for each larva, inside plant stems or holes in trees or man-made structures, such as fences and brick walls.
MacIvor monitored more than 200 artificial nest boxes placed in backyards, parks and gardens across Toronto as part of his long-term research into urban bees and wasps. When the cells were opened up this winter, it was instantly clear that something was different about them.
Nests for the Megachile campanulae, a species native to southern Ontario that normally uses plant resins such as pine sap to build nests, included a substance that looked like chewing gum — so much so that MacIvor popped some in his mouth to taste it.
“It didn’t really taste like anything, but it felt more plasticky,” he said.
To figure out what the materials were, MacIvor turned to his friend Andrew Moore, supervisor of analytical microscopy at the University of Guelph. Moore used an electron microscope and other powerful tools to identify the elements and polymers used in the nests.
They found that the gum-like substance came from polyurethane-based building sealants, such as window caulking. And another species — the Megachile rotundata, which builds nests by cutting leaves and bonding them together — chewed off bits of polyethylene-based plastic bags to build some of their cells.
All the larvae in cells that contained plastic survived to adulthood, the study found.
It’s not clear why bees turned to plastic, especially in areas where leaves and tree sap are still widely available, MacIvor said. One theory is that bees are opportunistic — they will use the closest suitable material for building, rather than the best material, to spend less time away from their nest and cut down on the risks they face while they’re out on a mission. And with more plastic infiltrating our environment, bee species that can adapt to it will be more successful.
While there has been a lot of attention paid to the plight of the honey bee in recent months, wild bees are also vital because they help maintain the city’s biodiversity, MacIvor said. Plants of all kinds — from the native species growing in our ravines to the vegetables growing in our gardens — fare better if they are visited by many different species of pollinators.
“The agricultural crops and plants we depend on are significantly affected by wild bee populations,” he said.
“The more we know about wild bee populations, the more secure our food supply will be.”