Monarchs and Milkweeds

Monarch butterfly (orange and black with white spots at the edges of its wings) resting on the end of a Common Milkweed flower (purple flower); green leaves in backgroundThe Monarch (Danius plexippus, Nymphalidaeae family) is probably the most well-known of Ontario’s butterflies to the general public. This is a very large butterfly (~10cm), smaller in size only to swallowtails. Adults can be seen in flight from June to October.

Typically, a monarch butterfly will live up to three months, but the last generation reared per year lives much longer - up to 9 months. This is because Monarch Butterflies are migratory. The eastern population of Monarch Butterflies are famous for their long distance migrations, sometimes travelling over 5000 km to Oyamel Fir (Abies religiosa) forests in the central Mexican cordilleras! Large populations of Monarch butterflies will spend the winter attached to the trunk and branches of Oyamel Fir trees. In the most densely populated areas, entire trees can be covered in butterflies and populations can number in the tens of millions. When spring arrives, Monarch Butterflies will begin returning to North America, and will only reach Ontario after 2 or 3 generations.

Photo: Monarch butterfly on Common Milkweed

In the autumn, usually during September, large amounts of Monarch butterflies congregate at Point Pelee National Park for a few days a year. What a sight to see! Migrating butterflies can also be viewed in other areas along the Lake Erie shoreline, including TTLT’s Hawk Cliff Woods nature reserve in Union, ON. 

Monarch larvae (caterpillars) only feed on species of Milkweed (Asclepias sp.). Luckily, Ontario has many species of Milkweed distributed across a wide variety of habitats. Common Milkweed (Asclepias syriaca) has beautiful pink flowers and grows in meadows and tallgrass prairies. Butterflyweed (Asclepias tuberosa) has uniquely shaped orange flowers. It is found in prairies, meadows, and oak savannas. Swamp Milkweed (Asclepias incarnata) has magenta flowers and is mainly found in herbaceous marshes and swamps. Poke Milkweed (Asclepias exaltata) has verdant green flowers and is excellently adapted to heavy shade, growing in forests, swamps and oak woodland-savannas. All of these host plants are palatable to Monarch caterpillars.

Monarch caterpillar (green, white, and black stripes) on the green leaf of a Butterflyweed plant; orange Butterflyweed flowers at the top middle of the photo above the caterpillar; background is mostly greenery and a strip of blue sky out of focusCommon Milkweed plant; has several purple bulbous flowers shooting out from long green stems and has large lobed leaves Swamp Milkweed flower (purple pink) with a baground of green leavesPoke Milkweed flower (white ends on thing green stems); background of leaves and forest

Photos (left to right): Monarch caterpillar on Butterflyweed, Common Milkweed, Swamp Milkweed, and Poke Milkweed.

Adult Monarch butterflies feed on a variety of plants for nectar. Native wildflowers are especially important for these purposes. During the autumn migration, Goldenrod (Solidago sp.) and Aster (Symphyotrichum sp.) are especially important for providing an adequate food supply.

Monarch butterflies are sometimes confused with another, very similar native species: Viceroy butterflies. Both species are part of the Nymphalidae (Brush-footed) family. Monarch butterflies can be distinguished from Viceroy butterflies by their larger size (around 10 cm wingspan for Monarchs, as compared to 8 cm for Viceroys), the black stripe across Viceroy hindwings (which is absent in Monarchs), and the way they fly (Viceroys have a faster and more erratic flight pattern). The visual similarity between the Monarch and Viceroy Butterfly is a commonly cited example of Mullerian Mimicry, where two toxic species appear to mimic each other for mutual benefit in protection against predators.

Monarch butterfly (orange and black with white spots along the wing edges) sitting on a yellow flower; some green leaves in backgroundViceroy butterfly (orange and black with white spots on the edges of its wings); black line across its hindwings; background of green leaves

Photos: Female Monarch butterfly (left) and Viceroy butterfly (right)

Monarch Butterflies are a designated Special Concern Species-at-Risk (SAR) in Ontario. Species-at-Risk is broadly defined as species declining in population that may be threatened with extirpation and/or extinction if measures are not taken to reverse population decline. Conservation organizations, including Thames Talbot Land Trust (TTLT), pay special attention to SAR species to help preserve the ecological requirements needed for SAR to thrive. These include monitoring projects for a variety of plant and wildlife as well as land stewardship. The southwestern Ontario Carolinian Life Zone (which includes London and TTLT’s working area) contains around 25% of Canada’s SAR, highlighting the importance of land conservation and habitat restoration in our region. TTLT has restored many meadows and tallgrass prairies across several of its nature reserves, which is critical habitat for Monarchs and Milkweeds. 

Ways that you can help Monarch Butterflies and other pollinators is by establishing native plant gardens, which have a myriad of ecological benefits. Native wildflowers are an important food source for many butterflies and insects. These native plant gardens may be especially impactful in urban areas and corn/soy plantations where good-quality habitat is rare. TTLT has two native plant gardens on two nature reserves, the Auzins Community Wildflower Garden at Hawk Cliff Woods and the Wardsville Woods Community Wildflower Garden, where anyone can come to enjoy the sights, sounds, and smells, but can also collect seeds from the plants to establish native plants in their own gardens and yards.

Conservation plays a pivotal role in reversing the decline of Monarch butterflies and other SAR. Land conservancies like TTLT, Long Point Basin Land Trust, and the Nature Conservancy of Canada are at the forefront of conservation efforts in the region around London. Conservation efforts will establish protected habitat and ecological restoration projects, which will have the most lasting impact on the populations of Monarchs, Milkweeds, and other SAR. Together, we can help our native species flourish and thrive!

All photos by Matthew Palarchio.

Written by Matthew Palarchio