The distinction between nectar plants and host plants is one of the most practical concepts in pollinator gardening. Nectar plants feed adult insects; host plants support the larval stage — eggs, caterpillars, and pupal development. Many gardeners plant nectar sources while overlooking host plants entirely, which limits the ability of their yard to support complete insect life cycles rather than just transient visitors.
This article covers host plant relationships for the most commonly observed bee and butterfly species in Ontario, with notes on how species composition shifts in Manitoba, Saskatchewan, Alberta, and British Columbia.
Oligolectic Bees: The Specialist Foragers
Roughly 25–30% of Canadian native bee species are estimated to be oligolectic — meaning they collect pollen from a restricted set of plant genera, sometimes from a single genus. For these bees, the presence of their host plants in a landscape is a prerequisite for reproduction, not merely a preference.
Examples of Oligolectic Bee–Plant Relationships in Ontario
- Andrena spp. (mining bees) — many species are specialists on willows (Salix), oaks (Quercus), or early-blooming spring ephemerals.
- Colletes inaequalis — collects pollen primarily from spring ephemerals including Mertensia and Claytonia.
- Melissodes spp. (long-horned bees) — specialists on the aster family (Asteraceae), particularly Helianthus, Ratibida, and Rudbeckia.
- Hesperapis spp. — restricted to Oenothera (evening primrose) in prairie regions.
Generalist bees — including the common eastern bumblebee (Bombus impatiens), which is found throughout Ontario and Quebec — visit a wide range of plant families. A yard with diverse native plantings will support bumblebees regardless of which specific species are chosen, but specialist bees require their preferred pollen sources to be present.
Host Plants for Butterflies: Beyond Nectar
Butterfly larvae are often highly specific in their plant requirements. Adult butterflies can feed on nectar from a wide range of flowers, but females oviposit only on plants that the emerging caterpillars can eat. A yard without larval host plants will see butterfly visitors but will not contribute to butterfly reproduction.
Monarch Butterfly (Danaus plexippus)
The monarch's dependence on milkweed (Asclepias spp.) for larval development is well documented. In Ontario, the most commonly planted milkweed species are:
- Common milkweed (Asclepias syriaca) — tall, fragrant, spreads by rhizome; suited to larger gardens and naturalized edges.
- Butterfly weed (Asclepias tuberosa) — compact, orange-flowered, drought-tolerant; does not spread aggressively.
- Swamp milkweed (Asclepias incarnata) — pink flowers, tolerates wet to average soil; useful in rain gardens or low areas.
Tropical milkweed (Asclepias curassavica) is not native to Canada and should not be planted as a monarch host substitute. Research from conservation groups and the Ontario government's monarch resources notes that non-native milkweeds may disrupt monarch migration cues in warmer climates where they do not die back naturally in autumn.
Canada Tiger Swallowtail (Papilio canadensis)
This large yellow butterfly is found across most of Canada from the Maritimes to British Columbia. Larval host plants include:
- Trembling aspen (Populus tremuloides)
- White birch (Betula papyrifera)
- Black cherry (Prunus serotina)
- Chokecherry (Prunus virginiana)
These are generally trees and shrubs rather than perennials — a yard that includes even one native tree species such as trembling aspen or white birch provides larval habitat that a bed of perennial flowers cannot replicate.
Black Swallowtail (Papilio polyxenes)
Larvae feed on members of the carrot family (Apiaceae). Native host plant options include golden Alexanders (Zizia aurea) and wild carrot relatives. Parsley and dill, while non-native, are also used and are more practical in small gardens.
Painted Lady (Vanessa cardui)
A generalist that uses many plant families, including thistles (Cirsium spp.), which are often removed from yards. Native thistles including field thistle (Cirsium discolor) support both larvae and a range of nectar-feeding insects and should be distinguished from invasive European thistles before removal.
Bee Host Plant Summary by Province
| Region | Key Native Bee Groups | Priority Host/Pollen Plants |
|---|---|---|
| Ontario / Quebec | Bombus, Andrena, Halictus, Megachile | Salix, Rudbeckia, Echinacea, Solidago, Monarda |
| Prairie provinces | Bombus, Osmia, Melissodes, Hesperapis | Dalea, Ratibida, Gaillardia, Helianthus, Oenothera |
| British Columbia | Bombus, Osmia, Colletes | Ceanothus, Camassia, Allium, Sedum |
| Atlantic provinces | Bombus, Andrena, Lasioglossum | Solidago, Symphyotrichum, Rudbeckia, Vaccinium |
Cavity-Nesting Bees and Stem-Nesting Habitat
Many native bee species do not nest in the ground at all — they use hollow plant stems, beetle tunnels in dead wood, or natural cavities. This means that the structure of a yard matters as much as the plant species selected.
- Leave standing dead stems: many Megachile (leafcutter bees) and Osmia (mason bees) use hollow or pithy stems of plants like Joe Pye weed, goldenrod, and sunflower.
- Avoid shredding leaf litter completely: some ground-nesting species overwinter in or under decomposing leaves.
- Retain dead wood: beetles create tunnels that are subsequently used by mason bees.