There’s something about the monarch butterfly (Danaus plexippus) that captures the hearts and imaginations of many. It has become the insect of choice of many states,1 a symbol of pollinator conservation, and has even inspired a record-breaking paragliding adventure following its migratory path!2
What interests me about the monarch is its beauty and resilience in face of fragility and adversity. The monarch has adapted in clever ways to deal with inclement weather, predators, and a long migration. This article touches on these and other fascinating abilities of the monarch and what you can do to help protect this beautiful butterfly.
Monarch Butterflies: Resilience in the Face of Fragility and Adversity
When I think of the monarch’s fragility, I think about their delicate wings and vulnerability to cold.
Butterfly wings are made from fine scales that are susceptible to damage from rain, predators, and mishandling from humans. Brushing up against a butterfly can cause breakage and damage to the scales and fine veins that run through the wing.3 This poses a big problem for butterflies who rely on their wings to move and regulate their internal temperature.
Like other butterflies, monarchs are cold-blooded (ectotherms) relying entirely on external sources of heat to elevate their core temperature to functioning levels.3 When the weather is chilly and cloudy, they are near helpless. Anything below 12.7°C (55°F) and they aren’t going anywhere.4 Add to that a windy day or a predator and you’ve got one miserable butterfly.
Despite these fragilities, make no mistake, monarchs are no wimps! They’ve evolved several protective mechanisms to get them through their day-to-day.
To combat the cold, monarch butterflies are experts in behavioural thermoregulation. When the temperature is cold, they shiver to warm themselves enough to crawl up vegetation and bask in the sun.4 Butterflies bask with their wings open, like solar panels, absorbing the heat and warming up their flight muscles.4
Animals that derive their energy from sun basking are called heliotherms. The dark scales on the monarch’s wings make them particularly good at converting light into heat.3 If you’ve ever worn a black t-shirt on a hot summer day, you know what I’m talking about. Black absorbs more wavelengths and more heat than light colours.
If a monarch, or any butterfly for that matter, loses too many wing scales it can negatively affect its ability to absorb heat and may lead to death.3
Long Migration and Anti-Aging
A testament to their resiliency, eastern monarchs complete one of the longest insect migrations in the world!5 They fly thousands of kilometers (+4800 kilometers / 3000 miles!) each year from Canada and the United States to their winter grounds in central Mexico.6 While not all monarchs migrate, millions of them do. Some make the journey in one generation, while others take 3-5 generations to complete it.7
It’s the newly hatched, late summer-developing caterpillars that make the trip to Mexico to escape freezing temperatures in Canada and dying host plants.7 Anticipating winter, these monarchs delay their reproductive development (reproductive diapause) in preparation for the migration south.7
Incredibly, delayed reproduction prevents aging in migratory monarchs! This allows them to live an extra 6–8 months to migrate south, overwinter, and remigrate north in the spring.7 In comparison, other monarchs will only live for 2-6 weeks.8
Expert Navigation Skills
The migratory voyage from Canada to Mexico is no joke! It takes remarkable navigational skills on the part of monarchs. A lot of research has gone into trying to understand this skill. As it turns out, monarchs are “compass navigators” using the sun and earth’s magnetic field to find their way around.
Monarchs can use the sun as a reliable compass throughout the daytime hours. Neurons in their antennae track time while neurons in their eyes track the position of the sun.9 This allows them to stay on course as the time of day changes. Scientists thought this solved the mystery of monarch navigation until they witnessed the butterflies flying on course on cloudy days! This led to more head scratching and experiments. Eventually, they were able to demonstrate that monarchs also rely on the earth’s magnetic field to stay on course.10
As if this isn’t impressive enough, monarchs have evolved to “detect wind direction and compensate for drift due to prevailing wind speed and direction.”7 To save energy, they will passively ride thermals favouring land routes with updrafts over travelling across large bodies of water with none.11
Poison for Lunch?
If the monarch’s solar panel wings, long migration, and expert navigation skills don’t impress you, how about their ability to turn themselves into a poison cocktail!?
Monarch caterpillars, also known as larvae, feed exclusively on milkweed plants to survive. Milkweed contains a poisonous sap which harms most animals, but monarch caterpillars have evolved to feed on it.
A hungry monarch caterpillar can consume an entire milkweed leaf in less than 5 minutes!12 Toxins from the milkweed sap are then stored in the monarch’s body through metamorphosis.13 When the monarch emerges as a butterfly it “contains the same foul-tasting phytochemicals as the hungry caterpillar.”13 As a result, the monarch becomes poisonous to predators.
Müllerian Mimicry: Monarch or Viceroy?
The bright colours of the monarch’s wings are actually a warning sign to hungry predators, “eat me and you’ll suffer!” The use of bright colours to warn off predators is know as aposematism.13 This warning sign has come to benefit the viceroy butterfly (Limenitis archippus) who mimics the appearance of our orange friend. It’s hard to tell them apart, but the viceroy has an extra black line across its hind wings.”14
The viceroy is not nearly as poisonous as the monarch, but its larvae feed on willows which contain a bitter tasting compound called salicylic acid that can cause sickness.13 Whether a predator targets the viceroy or the monarch, it learns to associate the bright orange colours with danger thereby benefiting both insects.13 This type of mimicry is called Müllerian mimicry and is defined as “a form of biological resemblance in which two or more noxious, or dangerous, organisms exhibit closely similar warning systems, such as the same pattern of bright colours.”15
Threats to Monarchs
The monarch shows great resilience in the face of fragility and adversity, but it is no match for human-caused environmental destruction. There are three major threats to monarch populations: “deforestation of wintering forests in Mexico, disruptions to their migration caused by climate change, and the loss of native plants along their migratory corridors.”5
In Canada, the monarch is listed as endangered under the Species at Risk Act. And, just last month, the International Union for the Conservation of Nature declared the monarch butterfly as endangered. The stats are grim, the eastern North American population has “declined by more than 50% in the past 15 years.”16 More grim still, “in the last two decades, the population of monarchs overwintering in Mexico has declined from an estimated 1 billion to fewer than 100 million.”17
In Canada, conservation efforts have focused on the loss of breeding and nectaring habitat and the elimination of pesticides.16 The impact of conservation measures here are dependent on measures taken to protect overwintering territories in Mexico, which are threatened by habitat loss caused by logging and climate change.18 To help the monarch, scientists, community members, and NGOs in Mexico have been monitoring monarch populations, establishing conservation areas, encouraging plant diversification, and planting pollinator gardens throughout the country.18
The monarch is of cultural importance to many Mexicans. Its migration coincides with El Día de los Muertos, a time to celebrate the lives and memories of friends and ancestors who have passed.19 To some, the butterfly symbolizes the “returning spirits of loved ones who have died.”5
Despite its cultural importance, some Mexican communities have come to rely on monarch forests as a resource.17 Conservation then is a complicated balance between social/cultural, economic, and political issues. With a central question being, how to prioritize community well-being and conservation? It’s a question that is not unique to Mexico, but includes habitat conservation in Canada and befalls all contemporary conservation efforts.
What Can You Do To Help? Plant Milkweeds and Document Species
While large systemic changes are needed to protect the monarch and its habitat, there are some things you can do to help monarchs here in Canada. In eastern Canada, you’ll find monarch caterpillars chomping down on common milkweed (Asclepias syriaca) and swamp milkweed (Asclepias incarnata). If you’re looking for a way to help monarchs, planting these species is a good start.
Milkweeds are easy to grow from seed and can be collected from mature pods in early fall. You might also find seed packets at gardening centres. Planting should happen in the fall or spring. If you are planting in the spring, milkweed seeds need to be cold stratified first (here’s a guide!). After being stratified, plant as soon as temperatures reach 15°C or warmer.20
Both common milkweed and swamp milkweed will spread through seeds and underground rhizomes.20 Common milkweed may be best suited for large plots or pots as it is quite aggressive.20 Swamp milkweed is a less aggressive spreader.
You can also help scientific research by documenting monarchs and milkweeds in your area using iNaturalist. iNaturalist is used by researchers to study biodiversity, species distribution, and the impacts of climate change. Some conservation groups have been using iNaturalist as a way to track monarchs and their habitat.
Here’s how to identify common milkweed and swamp milkweed:
Common Milkweed (Asclepias syriaca)
Common milkweed grows in meadows and waste areas with plenty of sunshine. It can grow up to 4 feet and has opposite, smoothed-edged leaves, that are ovate to oblong.21 The flowers are a beautiful light pink and found on spherical umbels.21 They are highly fragrant. When cut, common milkweed exudes a white sap.
Swamp Milkweed (Asclepias incarnata)
Swamp milkweed prefers damp areas like the freshwater shorelines of ponds, rivers, and lakes.21 Its leaves are more lance-shaped than common milkweed.21 Its flowers also grow on umbels, but are less spherical and a deeper pink-purple colour. Swamp milkweed also exudes a milky sap when cut.
What Other Plants Attract Monarchs?
In its butterfly form, the monarch subsists entirely on an all-liquid diet, preferring the nectar of brightly coloured flowers.20 Some of their favourites include: Canadian goldenrod, wild bergamot, New England aster, black-eyed Susan, common yarrow, boneset, and red clover.16,20 Planting a wide variety of blooms that are closely clustered together helps draw monarchs to your garden.20 Monarchs will also roost in pines, conifers, maples, oaks, pecans, and willows.16
There are other steps you can take to help these butterflies, including avoiding pesticides and other harsh chemicals in your garden. You can also add a shallow water source with partially submerged stones to provide perches for monarchs while they drink.20 Placing large stones in and around your garden can also act as warm basking areas.20
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1 “List of U.S. State Insects.” Wikipedia.
2 Jordan. “Slocan Valley Man Paraglides From Mexico To Canada: Sets A World Record.” Kootenay Mountain Culture.
3 Horton. “Will a Butterfly Die If I Touch Its Wings?” How Stuff Works.
4 Masters, Malcolm, and Brower. 1988. “Monarch Butterfly (Danaus Plexippus) Thermoregulatory Behavior and Adaptations for Overwintering in Mexico.” Ecological Society of America.
5 “About Monarch Butterflies.” WWF.
6 Bittel. 2017. “Monarch Butterflies Migrate 3,000 Miles—Here’s How.” National Geographic.
7 Reppert and Roode. 2018. “Demytifying Monarch Butterfly Migration.” Current Biology.
8 Oberhauser. “Monarch Butterfly Frequently Asked Questions.” US Forest Service.
9 Gill. 2016. “Great Monarch Butterfly Migration Mystery Solved.” BBC News.
10 2014. “Monarch Butterflies Use a Magnetic Compass During Migration.” Entomology Today.
11 Sarikonda. 2014. “Fall Migration – How Do They Do It?” Monarch Joint Venture.
12 “Frequently Asked Questions.” Save Our Monarchs.
13 Manning. 2014. “Butterflies: Tougher than You Think!” Bang Science.
14 Chandler. 2018. “Monarch Lookalikes and How to Tell the Difference.” Save Our Monarchs.
15 “Müllerian Mimicry.” Britannica.
16 Nova Scotia Department of Natural Resources and Renewables. 2021. “Recovery Plan
for Monarch (Danaus plexippus) in Nova Scotia.” Nova Scotia Endangered Species Act
Recovery Plan Series.
17 Linthicum. 2019. “To Save the Monarch Butterfly, Mexican Scientists Are Moving a Forest 1,000 Feet Up a Mountain.” Los Angeles Times.
18 Rendón and García Serrano. 2020. “Conservation of Monarchs in Mexico.” The Monarch Joint Venture.
19 Morris. 2020. “Monarchs and Día de Muertos in Mexico.” The Monarch Joint Venture.
20 Walker. 2013. “How to Build a Butterfly Garden.” Canadian Geographic.
21 Boland. 2015. Wildflowers of New Brunswick. Boulder Publications.