Soft-stemmed, or herbaceous, plants provide nectar and pollen in spades. As such, they are the focus of most pollinator gardens. Beebalm, wild bergamot, Joe pye weed, anise hyssop, sunflowers, coneflowers and violets top the recommended species lists for pollinators, and rightly so as they attract a multitude of flying insects.
As an example, many caterpillars (the larvae stage of butterflies and moths) consume the leaves of native trees and shrubs in addition to or instead of those of herbaceous plants. As adults, butterflies are far less picky, consuming the nectar of many flowers.
This specialization (a close evolution-based relationship between insect and plant) is most pronounced at the larval stage. Douglas Tallamy beautifully and thoroughly demonstrates the connection between the larval stage of butterflies (caterpillars) and woody plants in his revolutionary book, Bringing Nature Home. Tallamy recently presented on this phenomenon and its relevance to gardens as part of WWF-Canada’s Garden for Wildlife webinar series.
Bees also rely on woody native plants for food, shelter, nesting material and sites. Examples include the multitude of small to large-sized bees that feast on dogwood and cherry blooms; leafcutter bees that line their nests with redbud leaves; and small carpenter bees that construct nests in the pithy stems of elderberry, raspberry and sumac. Trees and shrubs are a crucial part of pollinators’ lives.
Although all native trees and shrubs contribute to the ecological health of our gardens and city, some species are more beneficial than others. They support larger numbers of wildlife species, including pollinators. This information is helpful for those of us with limited garden space.
Let’s look at Tallamy’s top trees and shrubs for caterpillar support, as well as a couple of others that support swallowtail butterflies. 
Paper birch (Betula papyrifera)
This tree is popular with landscapers and gardeners for its exfoliating bark, and with wildlife for this and other reasons. Many insects shelter under the bark, and birds and small mammals consume birch seeds and flowers.
Tallamy ranks birch as the fourth most supportive group of trees for butterfly and moth caterpillars.
Pin cherry (Prunus pensylvanica) and black cherry (Prunus serotina)
Native cherries are excellent sources of food for both vertebrate and invertebrate wildlife, including many insect pollinators.
Tallamy ranks cherries as the third most supportive group of trees for butterfly and moth caterpillars.
Pussy willow (Salix discolor)
This shrub is one of many willows native to southern Ontario. Small bees and flies make good use of its pollen and nectar, which is available before that of many soft-stemmed plants.
Tallamy ranks willows as the second most supportive group of trees and shrubs for butterfly and moth caterpillars.
Red oak is a biodiversity superhero, along with other native oaks. Tallamy gives oak trees top marks for their support of butterfly and moth caterpillars, and their support of wildlife in general.
Spicebush (Lindera benzoin)
This shrub, which is native to the Carolinina ecozone, has high wildlife and landscape value. It blooms early in the spring, produces nutritious berries that attract birds, and has fragrant leaves, which can be used to make tea. Spicebush flowers are a favorite of many butterflies, and the leaves are food for spicebush swallowtail caterpillars.
Tulip tree (Liriodendron tulipifera)
Tulip tree has a special place in the hearts of swallowtail butterfly fans as it hosts the caterpillars of eastern tiger swallowtail. Its large saucer-shaped blossoms also attract miscellaneous flies, beetles, bees.
This blog was written as part of Project Swallowtail. Residents of the project area are encouraged to plant native species to support these butterflies and other pollinators. Learn more about this project, and plant pollinator-supporting trees and shrubs through the subsidized LEAF Backyard Tree Planting Program.
This blog was written by Colleen Cirillo, a LEAF Board Member and Project Swallowtail Volunteer Manager. She lives in west Toronto with her family, where she maintains a small but mighty native plant garden.
The Backyard Tree Planting Program is supported by the City of Toronto, the Regional Municipality of York, Durham Region, the City of Markham, the Town of Newmarket, the Town of Ajax, the City of Oshawa, the City of Pickering, the Township of Scugog, the Town of Whitby and Ontario Power Generation.