Milkweed is not a weed!

Stepping into Nature - Minden Riverwalk

Milkweed is not a weed!

Minden, Ontario K0M 2A1, Canada

Created By: Haliburton County Master Gardeners


You can see some “pollination powerhouse plants” along the riverbank here. In addition to the yellow Goldenrod (Salidago species) and White Panicle Aster (Symphyotrichum lanceolatum), Common Milkweed (Asclepias syriaca) can also be seen in all its splendid glory.

Why do we now love native Common Milkweed, while once we treated it as a noxious weed? For the monarch butterflies of course! We know that monarch butterflies lay eggs on milkweed plants in our region, grow into caterpillars, pupate and emerge as beautiful orange butterflies and then embark on a 4000km flight to Mexico where they overwinter. Monarchs are also a threatened species being significantly impacted by pesticide use and habitat loss. This news article from 2022 has some interesting information on the monarch butterfly:

What steps can you take to support pollinators like butterflies? Consider planting a “Haliburton County Pollinator Garden”, filled with the kinds of native plants you’ll find along the Minden Riverwalk. These include trees, shrubs, flowering plants and sedges/grasses. The Haliburton Master Gardener native plant guide will be a good reference resource for you. Avoid the use of herbicides or pesticides on your property and in your gardens and leave stems of grasses and flowers standing in your garden in the fall to give overwintering insects a place to shelter.

Did you know that Common Milkweed leaves are eaten by both monarch caterpillars and butterflies? And those leaves contain a compound – glycosides – that make the monarch caterpillars and butterflies toxic to predators. Milkweed plants are the only food source for monarch caterpillars. Did you find some monarch eggs, caterpillars, pupae or butterflies on your walk today?

U-Links Species Profile:

Red Milkweed Beetle, Tetraopes tetrophthalmus

A common association to milkweed plants is the monarch butterfly, due to its popularity and use as a food source for caterpillars (Rhodes, 2022), however another species with an even stronger reliance on milkweed is the Red Milkweed Beetle (Tetraopes tetreophthalmus). Red Milkweed Beetles are a univoltine, specialist species (Erwin et al., 2014), specifically attracted to common Milkweed (Asclepias syriaca.). Univoltine insects are species that only produce a single litter/brood of offspring, in a single year. This insect is a specialist to Common milkweed, relying entirely on the plant to host its entire life stage, but also to host the next clutch of red milkweed beetles in the next season.

The Milkweed Beetle life cycle flows in tandem with the Milkweed plant, with peak colony size being reached at the height of the blooming period of the milkweed (Holdrege, 2010). Their life cycle is divided into four stages, which is known as holometabolous (Rhodes, 2022). The first of these stages is the egg stage. Female Red Milkweed beetles will lay their eggs at the base of the plant, or at a nearby plant stalk (Rhodes, 2022). Once hatched, the second phase begins, which is known as the larval stage. Newly hatched larvae have a wormlike morphology, burrowing into the ground to feed on the roots and rhizomes of the plants (Reagel et al., 2002). It is at this stage where the insect will consume the most food. The third stage is the pupae stage, where it spends time transforming into its final form, the adult phase. The adult phase is where the insect is the most recognizeable, as well as when the insect will feed at the top of the plant and reproduce (Rhodes, 2022). Adults feed on the flowers and foliage, with the larger plants being the most common grounds of congregation (Reagel et al., 2002). These beetles are also a pollinator species for milkweed

Adults are typically 1.27cm in length, and can be longer due to the size of their antenna, males however are typically smaller than females (Rhodes, 2022). The red and black colouration is a signal to other animals that it contains a toxin known as cardenolide (Erwin et al., 2014), which it acquires through the consumption of common milkweed. The toxin that is transferred to the larvae during its mass feeding period does not affect the beetle, making it a resilient herbivore. Adults will still contain the toxin after its final development, making it an unpleasant meal to many other predators.

Researcher: Caleb Brown, Trent University

U-Links Species Profile:

Monarch Butterfly, Danaus plexippus

The monarch butterfly is one of the most remarkable and most studied insects of all time. Dawning the infamous orange and black colouration, with white spots along its thorax, forewing and hindwing, this species has become renowned for its beauty as well as its use in educational settings. It is not uncommon for the monarch butterfly caterpillars and cocoons to be used for educational purposes in classrooms and in butterfly conservatories, allowing students and the citizens alike to enjoy their magnificence.

The monarch butterfly is also renowned for its massive migration from Canada through the United States and Mexico annually to their overwintering grounds (Jones, 2004). This journey can be upwards of 4000 kms in length, an extensive flight for such a small insect.

Monarch butterflies rely heavily on Milkweed plants. Adult monarchs will lay their eggs on milkweed leaves, which will provide a significant food source for the caterpillars once they have hatched. Milkweed plants are the only source of food for monarch caterpillars, making them specialist species in their early years. Of all the milkweed plant subspecies, the common milkweed is what hosts and feeds 90% of Monarch caterpillars.

The reliance on milkweed has created an ability to digest a toxin within the milkweed plant, known as cardenolide (Jones et al., 2019). Caterpillars are able to ingest, and sequester the toxic substance produced by milkweed, making themselves toxic if ingested and can induce vomiting in some birds, making them an undesirable food source for most avian predators in Canada (Fink and Brower, 1981).

The monarch butterfly is classified as endangered due to major losses in milkweed plants. Agricultural pesticides, urban development and roads have been attributed factors to the decline of this species (Pleasants, 2016).

Researcher: Caleb Brown, Trent University

This point of interest is part of the tour: Stepping into Nature - Minden Riverwalk


Leave a Comment



Download the App

Download the PocketSights Tour Guide mobile app to take this self-guided tour on your GPS-enabled mobile device.

iOS Tour Guide Android Tour Guide



Updates and Corrections

Please send change requests to