As I parked next to 574 Boston Ave. on the Tufts University campus in Medford, a monarch butterfly fluttered above the adjacent pollinator garden. To see a butterfly species I typically associate with fields of wildflowers flying among multi-story cement buildings and heavily trafficked roads seemed surreal.
“Monarchs are one of the most common native butterfly species found in cities,” said Elizabeth Crone, Professor of Biology at Tufts.
“Monarchs can smell milkweed from a football field away,” explained Atticus Murphy, a PhD student in the Tufts biology program.
“Insects have relationships with native plants,” added Nicholas Dorian, also a Tufts PhD student. “The smell and chemicals from the plants attract certain insects. Milkweed provides nectar for monarch butterflies and leaves for monarch caterpillars to feed on.”
The trio of biologists are part of the Tufts Pollinator Initiative, which has resulted in the establishment of a 600-square-foot pollinator garden and three smaller adjacent flower beds at 574 Boston Ave., as well as several other pollinator gardens on the Tufts campus.
Dorian and PhD student Jessie Thuma run the initiative, and are advised by Crone and Professor George Ellmore. Other graduate students, undergraduates, post-doctoral researchers, and the Tufts Facilities grounds team are also involved with the project. Funding comes from the Tufts Green Fund.
“The pollinator project started in 2019,” said Crone. “Every year we’ve added new gardens.”
In addition to the flagship pollinator garden, gardens have been planted at Tisch Library, 527 Boston Ave., and the Science and Engineering Complex.
The cement flower beds used for the project existed from when the buildings were first built, said Crone.
Motivation for the pollinator initiative involved several factors.
“Insect populations are threatened,” said Dorian. “We wanted to create habitat for insects. Cities are frontiers in insect conservation.”
Crone emphasized there’s also an aesthetic component.
“Pollinator gardens are very beautiful,” she said.
But the gardens aren’t just for insects.
“These gardens are for pollinators and for people,” said Dorian. “Pollinator gardens can also be used for learning and demonstrations, and to create a relationship with urban nature.”
Almost on cue, a bright yellow goldfinch landed on an echinacea plant and began feeding on the seeds.
The pollinator gardens contain some 30 species of native wildflowers, including mountain mint, goldenrod, sunflowers, bee balm, and penstemon, said Dorian. And the researchers have documented more than 120 pollinator species in the gardens.
“Lots of native insects live in the city,” said Dorian. “It’s remarkable how much pollinator biodiversity there is.”
“It’s not unusual, though,” said Murphy. “There’s a subset of bees, wasps, and butterflies that live in places like this. Forty to fifty percent of Massachusetts bee species can be found in urban settings. It’s amazing.”
The researchers said in addition to monarchs, they frequently see skipper butterflies and non-native cabbage white butterflies.
“The giant swallowtail butterfly is the single most spectacular pollinator we’ve seen at the Tufts gardens,” said Crone. “It’s huge — the size of your hand. They’re rare to see around here. They may be moving north because of climate change.”
Dorian showed me a collection of mounted pollinators including hover flies, wasps, beetles, and bees. Some bees, like bumblebees and non-native European honeybees, were familiar. Others, including cuckoo bees, leaf-cutter bees, cellophane bees, and sweat bees, were less well-known solitary bees.
“There are nearly 400 species of wild bees in Massachusetts, most of which are solitary bees,” said Dorian.
Unlike honeybees and bumblebees, which are social bees, solitary bees do not live in hives or make honey, Dorian explained. Each female builds and provisions her own nest. Because they do not have a hive to protect, solitary bees rarely sting.
To help solitary bees nest, the Tufts team mounted short sections of PVC pipe on wooden poles in the pollinator gardens. The pipes were filled with small cardboard tubes that resembled drinking straws.
“The tubes are like bee hotels,” said Murphy. “They have different size holes for different size bees.”
Solitary bees usually nest in small holes in the ground or in hollow plant stems.
“Gardeners can keep the entire life cycle of solitary bees in their gardens,” said Dorian. “Leave plant stems cut to 12 inches, and don’t till soil too deeply.”
In general, bees consume both pollen and nectar whereas other pollinators, like butterflies, only consume nectar, said Dorian.
When pollen rubs off pollinators’ bodies onto the stigma — the female part of a flower — fertilization of the flower’s ovules occurs, resulting in the development of seeds and fruit.
“Bees are actually better pollinators than butterflies because even though they eat pollen, they also get more pollen on their bodies that gets transferred to other flowers,” said Dorian.
There are questions whether European honeybees, many of which are raised by beekeepers, compete with native bees and other native pollinators for nectar and pollen. Richard Primack, a biology professor from Boston University, conducted a research project in Newton this summer that sought to answer that question. Primack also looked at whether pollinator gardens were adequately supporting native pollinators.
Primack and BU undergraduate students Selby Vaughn and Katia Landauer, visited pollinator gardens, other types of gardens, and vacant lots in Newton to determine what flowers native insects were visiting, and whether honeybees were competing with native pollinators. Over 300 plant species were surveyed.
“Honeybees, native bumblebees, and solitary bees were found on dozens of different plant species, but the greatest numbers visited flowers of non-native species,” Primack said. “Large numbers of pollinators also visited some native plants.”
Plants near honeybee hives were visited by similar mixtures of pollinators to plants growing farther away from hives.
“The fact that mixtures of honeybees, bumblebees, and other native insects were found visiting both native plants and non-native plants suggests honeybees are not so severely depleting the floral resources that other pollinators are excluded,” said Primack. “It remains to be seen if native pollinators would be more abundant with reduced honeybee densities.”
Primack found pollinator gardens provide pollen and nectar for some native pollinators. He said additional measures that could benefit native pollinators include mowing lawns and fields less frequently so native plants have a chance to flower, setting aside edges of yards and fields as unmown pollinator habitat, planting native wildflower meadows along with pollinator gardens in parks and other areas, and restricting use of herbicides and pesticides.
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