Monarch Butterfly

(Danaus plexippus)

Status: Endangered (International IUCN 2022, Federal COSEWIC 2016), Special Concern (Ontario ESA, 2008)

Table of Contents:

Species Identification
Diet
Habitat and Range
Biology and Behaviour
Similar Species
Threats/Reasons for Being Endangered
Conservation and Recovery Strategies
How You Can Help

Species Identification:

The Monarch Butterfly is a relatively large butterfly species, with a 93 to 105 mm wingspan. They have orange wings with black trim and two rows of white spots along the border of their wings. Their caterpillar form is large with white, yellow, and black bands. Before turning into a butterfly, the Monarch will form a chrysalis (cocoon) that is jade coloured with gold spots.

Diet:

Monarch Caterpillars feed exclusively on milkweed plants. The most commonly used milkweed species by Monarch Caterpillars in Ontario are Common Milkweed and Swamp Milkweed. Adult butterflies feed on the nectar of milkweed flowers, as well as wildflowers including goldenrods, asters, non-native Purple Loosestrife, and various clover species.

Map taken from World Wildlife Fund: https://wwf.ca/species/monarch-butterfly/

Habitat and Range:

The Monarch Butterfly can be found from Central America up into Canada. Their Canadian range can occur in all 10 provinces, but it is mainly concentrated within Southern Ontario and Southern Quebec. Monarchs are loosely divided into Eastern and Western groups but they are not genetically distinct. In late summer and fall all Monarchs in Eastern North America migrate to central Mexico to overwinter, while western populations of monarchs migrate to the south of coastal California.

Monarchs will live in three main types of habitats throughout their life cycles. Caterpillars will inhabit the same areas as milkweed for their source of food. These plants grow in open, sunny, and periodically disturbed areas such as roadsides, fields, meadows, wetlands, prairies, and open forests. Monarch Butterflies in their northern summer habitat will be found wherever they can find wildflowers to feed on, and in the winter they will live in the Oyamel Fir Forest of Central Mexico.

Biology and Behaviour:

Every year, Monarchs return to these habitats in Ontario by May to early June, after travelling up to 3,000 km from their overwintering locations in Mexico. Once they reach their summer habitat, they lay 300-400 eggs on the underside of the milkweed leaves. Once hatched, caterpillars eat continuously for up to two weeks, then form chrysalis (cocoons) and emerge as adult Monarch Butterflies. Approximately 10% of the monarchs that leave Mexico travel all the way to Canada. Most that arrive in Canada are the great grandchildren of those that left Mexico, as the adults that leave Mexico mate and lay eggs once or twice along the journey. While the butterflies are in Southern Ontario, they produce 3 or 4 generations, each living for 4 to 5 weeks. However, the adults that emerge in the late summer and early fall in Southern Ontario can live for up to 8 months. By early August to early November, Monarchs start heading south again to Mexico. However, they require staging areas in large trees on the north shores of the Great Lakes for resting, feeding, and waiting out poor weather before migrating over large bodies of water.

Similar Species:

The wing colourations on Viceroy Butterflies may look very similar to Monarchs. However, Viceroys are smaller than Monarchs and have a black line across their hind wings whereas Monarchs do not.

A Viceroy Butterfly

A Monarch Butterfly

Threats/ Reasons for being at Risk:

There are many factors that are negatively impacting the Monarch Butterfly, and while they are generally deemed low risk, they can build up and become larger issues. These issues include development, tourism and recreation, energy production and mining, roads and railways, human disturbance, and climate change. The two highest threats to the Monarch Butterfly are listed below:

1. Deforestation in Mexico: Monarch Butterflies have a very small overwintering range. Deforestation of the Oyamel Fir Forest through logging, urban, and agricultural development has resulted in significant losses and damage to the suitable overwintering habitat. The degradation of this critical habitat has exposed them to more extreme weather conditions, stressing the populations and increasing mortality. This loss of habitat has resulted in severe declines in the number of butterflies able to overwinter in the area. Moreover, the butterflies that do overwinter in the forest are confined to a very small area, making them vulnerable to significant impact as a result of severe weather events, predation, disease, or other localized disturbances. Climate models predict the amount of suitable forest habitat will continue to decline, and the frequency of extreme weather events will continue to increase as a result of the continued effects of climate change, resulting in mass mortalities of overwintering populations.

2. Herbicides and insecticides: The increasing use of herbicides in the agricultural sector has resulted in great declines in milkweed populations across the range of the Monarch, including in Canada. Neonicotinoid insecticide used by corn and soybean farmers is further negatively impacting milkweed populations. The insecticide can remain in the soil after its application, and is taken up by plants, including milkweed. The presence of this insecticide in the tissues of the milkweed can negatively impact the Monarch Caterpillars that feed on them, decreasing their fitness and therefore their chances of survival.

Conservation and recovery strategies:

Since the range of the Monarch Butterfly is so widespread, and the species is so well-loved throughout North America, its existence ensures protection of a wide range of habitats (and many other species) across the continent. Adult Monarch Butterflies are also excellent pollinators of many beautiful wildflowers native to Canada, and can be helpful pollinators in backyard gardens. As of July 2022, the International Union for Conservation of Nature (IUCN) declared the Monarch Butterfly as internationally listed as Endangered. While the Monarch Butterfly and their habitat in parks and on crown land is protected in Canada, most of their breeding habitat is on private land or in unprotected areas. This means that cooperation with organizations and the public is crucial to recover this species. More habitat protection and rehabilitation is needed for this species to thrive, especially in their overwintering habitats. It is also important for fertilizer and pesticide use to be studied and further reduced if deemed harmful to important insect species.

How can you help?

Record and submit sightings to The Land Between online and/or to iNaturalist. Your observations help scientists monitor and track Monarch Butterfly populations!
Plant milkweed in your garden, specifically Common Milkweed (Asclepias syriaca) and Butterfly Milkweed (Asclepias tuberosa), which grow in well-drained soil. You can also plant Swamp Milkweed (Asclepias incarnata), which grows in damper, marshy areas. Other butterfly friendly-flowers to plant that adult Monarchs can feed on include Purple Coneflower (Echinacea purpurea), Black-eyed Susan (Rudbeckia hirta), and Canada Goldenrod (Solidago canadensis).
Avoid the use of pesticides in your lawn and garden as they can be harmful to the plants on which Monarch Butterflies depend for food and laying their eggs.
Keep an eye out for Monarch and other butterflies on the road, and do not touch them in any of their forms if they do not need help.

Quick Facts:

Monarch Caterpillars avoid excessive predation by taking up and storing a toxin found in milkweed into their tissues, making them toxic to many predators that try to eat them
Some Monarch Butterflies travel up to 80 km per day on their journey North to Canada, or South to Mexico
Monarch Caterpillars eat constantly from the day they hatch to the day they form a chrysalis. Over this two week period, they increase their weight by 2000 fold!