Under invasion! Watch out for the Japanese knotweed plant

Aggressive species can penetrate concrete and starve local plant species of resources

Under invasion! Watch out for the Japanese knotweed plant

UTSG is under invasion by an unusual suspect — a thoroughly aggressive plant.

The culprit is Japanese knotweed, also known as Reynoutria japonica, which is a flowering bamboo-like species that has spread across Ontario and the rest of Canada.

Its population threatens infrastructure and native plant life, as the plant can penetrate concrete and rapidly overtake other plants in the race for nutrients and sunlight.

Knotweed, a plant native to East Asia, is thought to have been introduced to the rest of Canada through Nova Scotia in the 1880s. By 1901, it was grown in Niagara, Ontario for ornamental purposes. Its reach extends widely — an online map lists 63 sightings in Toronto alone.

Its large leaves can block sunlight from plants that grow closer to the ground, starving them of an essential resource for survival. Layers of decomposing stems and leaves shed by the plant can obstruct growth of native species. The space it takes up can reduce wildlife habitats too.

Knotweed also poses a threat to infrastructure because its roots can penetrate concrete. In one case documented in England, the plant grew through a wall and into a couple’s home — slashing the property’s retail value by over $400,000.

Now, it has invaded UTSG as well.

The Varsity confirmed two sightings of knotweed on campus. At the time of its survey in July, a very large plant was photographed overtaking sections of a garden attached to a student residence at St. Michael’s College, and a smaller plant was photographed growing on Sussex Avenue behind Robarts Library.

Two other clumps of knotweed were documented as dotting the western perimeter of UTSG on either side of Spadina Avenue. One was photographed at 698 Spadina Avenue, which is the site for a planned student residence building finalized earlier this year.

Controlling the spread of knotweed can be very difficult. The plants primarily grow offshoots through an underground plant stem, or ‘rhizome,’ which can reach a length of up to 18 metres.

The rhizome can be found as deep as two metres underground — meaning that overturning the entire top layer of soil is the best way to prevent the plants from spreading.

St. Michael’s may be home to the largest knotweed plant on campus

The knotweed patch at St. Michael’s College was photographed in the alley between McCorkell House and Sullivan House at 2 Elmsley Place and 96 St. Joseph Street, and Maritain House and Gilson House at 6 and 8 Elmsley Place. All are student residences. It was also visible from the quad behind Teefy Hall.

Knotweed plants have a distinctive appearance. Their hollow stems resemble bamboo once they mature, reaching up to three metres in height.

They have broad leaves shaped like a heart with a flattened base, which grow off the stem in a zig-zag pattern. The node where the leaf meets a stem is reddish-purple.

The plants blossom in late summer or early autumn, growing tufts of small white flowers.

At St. Michael’s College, the largest plant was photographed at over two metres tall and spreads out over about five metres, and pressed onto the side of a building.

Knotweed was observed growing on both sides of the paved alley, clearly demonstrating how its roots can push through and around concrete obstacles.

Three other locations nearby

The other Japanese knotweed plant on UTSG was photographed growing at the privately-owned house at 16 Sussex Avenue and near other homes. This is close to the Robarts Library and the Sussex Clubhouse, which houses many student organizations such as The Varsity and the Sexual Education Centre.

Another privately-owned property at 15 Glen Morris Street was photographed with knotweed plants growing in its backyard. The plants were spotted sandwiched between Graduate House, a residence building for graduate students, and the Early Learning Centre, which provides services for children of U of T students, staff, and faculty.

The final location was photographed just off-campus at 698 Spadina Avenue, beside the now-closed Ten Editions bookstore. It will be the site of a new student residence.

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How The Varsity identified the plants as knotweed

To initially identify the plants as knotweed, The Varsity followed identification guidelines prepared by advocacy groups. The visual identifiers — of having heart-shaped leaves, a hollow stem, and reddish-purple nodes were previously referred to in the article.

Tyler Jollimore, a Master’s student at Dalhousie University’s Department of Plant, Food, and Environmental Sciences, also confirmed that the sighted plants are knotweed in written correspondence with The Varsity.

He concluded the plants’ identity by examining photographs of the plants taken at the four sites listed in the article, which are included in the photo gallery above.

He added that well-informed observers can reliably identify the plant, even without his expertise as a Japanese knotweed researcher.

“So long as individuals have done their research, identification of Japanese knotweed is possible by anybody,” he wrote. “[The] appearance of Japanese knotweed makes it quite easy to identify as it tends to stand significantly taller than other herbaceous plants.”

The difficult task of eradicating knotweed

Knotweed spreads through stem cuttings and can quickly grow to colonize a new area, especially in a moist environment.

Once entrenched, the plant is very difficult to remove. Weather is no impediment, as it can endure harsh conditions and even survive floods.

The plant is especially effective at reproduction when growing alongside rivers. Its roots can break off and travel downstream, enabling it to start new growth in a different location. This is one of the ways it can spread quickly in a city near bodies of water.

Controlling knotweed populations with herbicides can take three to five years.

Physical removal alone is an ineffective strategy

One of the more common ways to eradicate invasive plant species is to cut the plant to reduce its height and diameter.

However, this physical method is not lethal to knotweed, as it can grow back again the following year. It can also make the problem worse. “Cutting could increase the chance of knotweed spreading,” noted Jollimore.

“People (more specifically children) may pick it up and play with [the plant remains], resulting in it being moved to another area,” he wrote to The Varsity.

Ecologists are currently studying effective means of knotweed control. Jollimore noted that according to the findings of a recent study he was involved in, “injections of glyphosate — a [herbicide] — can provide significant reduction in knotweed stem density in the year following the treatment.”

In this approach, every stem of the plant needs to be injected for the treatment to work. This can be labour-intensive, especially if an area contains a high density of knotweed.

“Using cutting and then spraying a herbicide to [prevent] regrowth one month later,” wrote Jollimore, could effectively reduce knotweed populations. Any removed portions of the plant must be disposed of to reduce the risk of spread via the cuttings.

Glyphosate is controversial as a likely human carcinogen. Ontario law has prohibited the use of glyphosate for plant eradication conducted for aesthetic purposes since 2009.

But the Ontario Invasive Plant Council, an advocacy group, wrote that the ban does not apply to glyphosate usage for knotweed removal. The plant’s eradication is motivated by the need to prevent damage to infrastructure and biodiversity, wrote the Council, which qualifies the plant as an exception to the ban.

As “glyphosate-based herbicides are significantly better than all other herbicide groups currently used for knotweed control,” according to Swansea University scientists, the herbicide’s application may still be the best approach for knotweed removal.

Invasive plants at U of T “physically removed” if discovered

Every treatment method against knotweed will require time and careful planning. Most treatments will damage the stems after the first year of treatment.

To prevent the spread of knotweed in the first place requires vigilance by local residents and plant owners.

“Be careful [when] accepting fill soil,” wrote Jollimore, adding that people should “use a keen eye when purchasing plants, as occasionally knotweed may be labeled as something else such as bamboo or Chinese rhubarb.”

Knotweed growth is hardly restrained by “unorganized, poorly thought out management strategies,” he continued. “You want to work smart, then hard — not the other way around.”

Mark Simpson, University of Toronto Director of Building Services, Grounds and Trades responded to The Varsity’s inquiry about sightings of Japanese knotweed on campus.

“The grounds department does, from time to time, find invasive plant species such as Japanese knotweed on University of Toronto property,” he wrote. “Such plant species are physically removed whenever they appear.”

A U of T spokesperson added that the knotweed sighting at St. Michael’s College was not on U of T property. The removal of knotweed at this location on campus is therefore not the responsibility of the grounds department, as the property of St. Michael’s College, which is a federated college, is not managed by U of T.

“The University of St. Michael’s College respects the environment, and follows the University of Toronto’s policy regarding invasive plant species,” wrote Michael Chow, Director of Facilities at St. Michael’s College, in a statement to The Varsity. “Our 11-acre campus is home to over 150 species of flowers, trees and other foliage, which our grounds team tends year-round. We’re aware of the plant in question and took appropriate action in late July.”

It’s important to report any sightings of the Japanese knotweed online, as earlier recognition of this invasive plant can help suppress its further growth.

Correction (August 13, 12:02 pm): A previous version of this article implied that U of T is responsible for removing knotweed at St. Michael’s College. A U of T spokesperson has written that the university is not responsible for this removal, as the property of St. Michael’s College is not under U of T’s management. The Varsity regrets this error.

Editor’s Note (August 15, 12:23 am): Additional photographs have been added to the article to provide visual documentation for all four knotweed sightings described in the article. The Varsity has also included further comments from Jollimore, which confirm that the photographs contain knotweed.

Editor’s Note (August 18, 9:47 pm): A statement from a St. Michael’s College representative has been added, who wrote that” appropriate action” was taken to address the two-metre tall plant sighted near 2 Elmsley Place.

Weeding down the environmental cost of cannabis cultivation

How yeast could revolutionize an unsustainable industry

Weeding down the environmental cost of cannabis cultivation

Canada has the world’s largest market for recreational cannabis. Its legalization last year lit the path to a ‘higher,’ more liberal future, and was a bold move that came at an opportune time for science.

Cannabis-related research and education are flourishing in this political landscape — the demand for cannabis expertise is going through the roof, creating a space that begs for attention from researchers.

But cultivating cannabis for both research and recreation comes at a cost: it is both expensive to produce at industrial scales and damaging to our environment.

With the many trailblazing studies on cannabis underway, an especially creative finding detailing a new cultivation technique was published in February as a letter in Nature. Dr. Jay Keasling’s lab at UC Berkeley engineered yeast to produce pure cannabinoids like tetrahydrocannabinol (THC) and cannabidiol (CBD). This discovery motivates a reconsideration of current cannabis production policies and strategies.

The ecological and economic costs of cultivating cannabis

A recent CTV News article titled “Canada’s largest outdoor cannabis farm ready for growth” reports that prior to the farm’s opening, most legal cannabis had been cultivated in indoor facilities.

This should be a cause for concern. The financial cost of these methods of production is superseded only by the environmental costs. The cultivation of cannabis is not only water- and nutrient-intensive, but also usually requires land clearing, causes agrochemical pollution, and erodes soil. The unenlightened idea of an outdoor farm could cause severe ecological harm and environmental degradation. 

The production of one kilogram of processed cannabis releases 4600 kg of carbon dioxide emissions into the atmosphere. That is the amount of carbon dioxide produced by 3 million cars in the US.

An indoor facility is an even worse prospect. A 2012 study published by Dr. Evan Mills in Energy Policy, analyzed a four by four by eight-foot module of indoor cultivation. The results show that it would require 13,000 kilowatt-hours per year for utilities such as high-intensity lighting, ventilation, pre-heating the irrigation water, space heating, and air conditioning within the indoor facility. At this rate, Mills estimated the financial cost of growing cannabis from electricity alone to be $6 billion per year in the US.

The environmental costs are even more astounding — fossil fuels have caused carbon dioxide levels to be raised four times the atmospheric usual. At this rate, Mills estimated that the production of one kilogram of processed cannabis releases 4600 kg of carbon dioxide emissions into the atmosphere. That is the amount of carbon dioxide produced by 3 million cars in the US. The ecological horror entailed would cause both Greta Thunberg and anyone who understands climate change to have nightmares.

A sustainable alternative to indoor and outdoor cultivation of cannabis

The environmental burden of producing cannabis is too costly using the current methods of cultivation. It would be a great mistake on the industry’s part not to consider alternatives. One beneficial method that could help solve these problems is the procedure co-outlined by Keasling.

The new method is said to cover the deficits of current cannabis production methods. The researchers created an experimental setup that would be cost-efficient, environmentally safer, and enable direct synthesis of THC and CBD.

By developing a fermentation process using brewer’s yeast, the scientists have engineered a way to produce cannabinoids from a sugar called galactose. The process could help rein in the carbon footprint and financial cost of cannabis cultivation, as well as enable efficient production of specific cannabinoids normally found in trace amounts of plant-cultivated cannabis. 

It could be a great breakthrough for Canadian researchers studying cannabis to investigate the application of this new method, along with companies that sell products imbued with THC and CBD, such as cannabis-derived oils.

Sustainably cultivating cannabis can have medical applications

By developing a fermentation process using brewer’s yeast, the scientists have engineered a way to produce cannabinoids from a sugar called galactose.

The efficient synthesis of THC and CBD through the sustainable yeast-based method could be especially relevant in medicine due to the effects of the isolated compounds on patients.

According to a research review on effects of THC on cognition, the compound can reduce activity in major parts of the brain, including the prefrontal cortex. THC is thus generally linked to impairment of cognitive abilities, as well as psychotic symptoms and anxiety. On the other hand, CBD, which is an antagonist of the cannabinoid receptor, increases activation of other major parts of the brain, such as the prefrontal cortex and striatum.

The review further concludes that CBD reduces anxiety, thus opposing the effects of THC. When subjects are given a combination of equal amounts of THC and CBD, in comparison to pure THC, it was observed that CBD subdued the detrimental effects caused by THC. The risks associated with CBD products are therefore thought not to be associated with CBD itself, but other cannabinoids that can be found in the product.

Controlling the THC:CBD ratio in potential medications derived from cannabis could hold promise in medical research. Dr. Lakshmi Kotra, a senior scientist at the U of T-affiliated Krembil Research Institute, illustrated the example case of Sativex in an interview with The Varsity.

Sativex is a Canadian drug that has a 50:50 ratio of THC and CBD and is usually given to patients with multiple sclerosis. There is anecdotal evidence that suggests that smoking cannabis has better effects than Sativex.

Another example demonstrating the importance of controlling for specific ratios of THC and CBD stems from research on potential treatments for schizophrenia. The effects of potential cannabis-derived treatments have been shown to vary based on the THC:CBD ratio, highlighting the importance of its control.

While scientists can extract pure cannabinoids from cannabis plants, it’s an expensive and arguably arduous method that produces low yields. New approaches such as the yeast-based methods could offer more efficient ways of producing these medically relevant compounds.

The wider impact of sustainable cultivation

It may be a great breakthrough for Canadian cannabis-based companies to investigate such innovative, ecologically safe, and cost-effective methods, and would also allow the nation to set an example for the world with progressive legislation. It would be a great showcase of sustainable development and economics — a perfect way to lay down roots for a new industry that is bound to thrive in the coming years.

We are creating history with respect to cannabis legislation and distribution. With the nation-wide legalization of cannabis, along with Germany and New Zealand importing Canadian-grown cannabis, it becomes imperative to pay attention to current methods of growth, the sustainability of which should be equally considered for its ecological and financial costs.

Saving the Great Lakes from ecological disaster

The consequences of climate change on our largest freshwater system

Saving the Great Lakes from ecological disaster

As summer approaches, students are exchanging their scantrons for swimsuits and pencils for popsicles. For many, summer plans will involve the Great Lakes.

The Great Lakes are an epicentre of recreational, economic, and ecological activity. 9.8 million Canadians, about a third of our country’s population, rely on them. Carved thousands of years ago by retreating glaciers, the Great Lakes are a unique ecosystem housing a fifth of the world’s freshwater.

However, concealed by the rolling waves and the glassy surface of the lakes is evidence of environmental damage caused by humans over the last few centuries.

We have not always been kind to the Great Lakes. Heavy human use of the lakes has resulted in habitat loss and fragmentation, the introduction of invasive species, and environmental pollution. The invasion of zebra mussels and clouds of green algae blooming from phosphorus runoff are just two consequences of human activity to make headlines.

More than 3,500 species of plants and animals call the Great Lakes home, and for some, this is the only place where they can exist. Faced with the growing consequences of climate change, the Great Lakes system is coming under even more stress and is possibly reaching a tipping point.

The Environmental Law and Policy Center report

In March, the Environmental Law and Policy Center (ELPC), an American non-profit advocacy group, released a report detailing the effects of climate change on the Great Lakes.

Although it is widely understood that the consequences of climate change – like rising temperatures and more extreme weather events – will affect everyone, this report also detailed specific consequences for those who live in the Great Lakes region.

Increasingly severe weather patterns will bring hotter, drier summers to the area, causing heat waves. They will also bring wetter springs and winters, which will trigger flooding and increased water flow.

From the early 1900s to 2015, the Great Lakes region experienced a 10 per cent increase in precipitation, compared to the rest of the United States, which had only experienced an increase of four per cent.

“We’re seeing more and more of these… powerful wind storms, rain storms, [and] thunderstorms in the summer, and more milder winters for sure,” said Dr. Harvey Shear, a professor of geography at UTM, who teaches courses on the Great Lakes.

However, the ELPC anticipates that by 2100, the Great Lakes region will have less moisture in the summer, leading to fewer periods of intense precipitation at the start of the season.

Intensifying heat will bring about more days with temperatures above 33 degrees Celsius. By 2100, the ELPC report predicts that the Great Lakes region will experience an additional 30 to 60 days of such temperatures per year.

These intensified patterns of precipitation and hotter temperatures will translate into devastating consequences for the environment and our society. Shortened growing periods, increased disease, and the rising prevalence of waterborne pathogens will directly affect humans.

Nothing new

While it may seem like a shock to find that the Great Lakes region will experience such severe changes in the near future, researchers are not surprised by some of these consequences.

“We have modified the Great Lakes over the last 400 years to the point where they’re almost unrecognizable from what we would have seen if we [went] back in time,” explained Shear.

A case in point is the St. Lawrence River, which has been carved out to accommodate human activities since 1680. Construction began for the St. Lawrence Seaway in 1954 to directly connect the Great Lakes to the Atlantic Ocean. The $470.3 million seaway enabled cities like Toronto and Chicago to expand their commercial shipping industries, bringing in more than $6 billion USD per year to the Great Lakes region.

However, the seaway’s completion resulted in the decimation of the system by invasive species like sea lampreys. Sea lampreys are circular-mouthed fish with hooked teeth that attach themselves to native fish, feeding on their bodily fluids and abandoning them to succumb to their wounds. During their parasitic stage, lampreys kill approximately 40 pounds of fish over 12 to 18 months.

Spiny water fleas, zebra mussels, and other invasive species have also found their way to the Great Lakes system through shipping freighters. When taking on water in their ballast tanks, which are designed to stabilize vessels that are unloading or taking on cargo, these ships will also take on waterborne invasive species. Zebra and quagga mussels, in particular, are known for clogging water intake pipes and being costly to remove.

As temperatures continue to rise, native inhabitants of the lakes will endure added stress from an ecosystem where they are already competing with their non-native neighbours, likely forcing these species to shift to more northern regions.

These concerns are not new — the original 1971 edition of Dr. Seuss’ children’s book, The Lorax, referenced the dire state of Lake Erie. In the 1930s, runoff from fertilizer and waste from humans and animals introduced phosphorus into the lake. Annual phosphorus input soared from about 3,000 tons in 1800 to 24,000 tons in 1960, after the introduction of the mineral in cleaning agents after World War II. The high phosphorus levels caused an overgrowth of algae, clouding the water and killing off other species in a phenomenon known as eutrophication.

State and provincial governments around Lake Erie took action to limit the addition of phosphorus to soap, and began working with local farmers to reduce the amount of phosphorus input by more than half. However, new sources of phosphorus appeared in the 1990s, returning phosphorus levels in Lake Erie to previous conditions.

These algal blooms are more than an eyesore. A species of cyanobacteria called Microcystis causes such harmful algae blooms by producing a toxin called microcystin. The toxin can cause diarrhea, vomiting, and in high enough quantities, liver failure in humans.

Microcystis gripped Toledo, Ohio in 2014, when Lake Erie was subjected to two harmful algae blooms that year due to a one-two punch of increased precipitation and warmer temperatures. The toxin overwhelmed the city’s water filtration system, leaving half a million residents without clean water for three days.

Not all strains of Microcystis produce this toxin, but researchers have found that warmer growing conditions have increased the prevalence of the toxic strain, suggesting that this phenomenon could become more prevalent in the future.

Although some of these consequences listed in the ELPC report are not a result of climate change alone, climate change could worsen their effects in the coming years.

The looming storm

The consequences of climate change are not so far off. Shear noted that significant shifts can happen quickly within a year or two, intensifying extreme weather events.

“With climate change you’re dealing with very long-term changes over decades which makes it easy to attribute extreme weather events to normal year to year variation,” said Shear.

A more tangible consequence of the changing climate, continued Shear, is the uptick of unpredictable weather events, such as violent wind storms. In fact, climate change may have caused the Toronto Islands and the Harbourfront to flood in spring 2017

Shear further explained that we have hardened the surfaces of urban areas with hectares of paved roads and roofs that don’t absorb water. “So when it does rain, there’s nowhere for the water to go but straight into the streams and into [the] lake.”

“[The] Lake Ontario water level was fairly consistent,” he continued, “and then the water level began to rise because of the rainfall and snowmelt… that [had] nowhere to go.”

Concurrent flooding in Montréal, due to extra water in the Ottawa River and St. Lawrence Seaway, denied the officials the option of draining Lake Ontario into the sea to lower the water level.

Although the islands reopened later that summer, visitor attendance was down for the rest of the season, costing the city approximately $5 million in lost ferry revenue, in addition to costs from property damage.

That 2017 flood should be a sobering sign that the Great Lakes will not stay the way they are for very long.

Economic damage

Viewing environmental damage through an economic lens helps put the consequences of changing conditions into perspective. The Great Lakes provide over 1.5 million jobs and generate $60 billion in wages annually for local workers. The regional economy of the Great Lakes system is valued at $6 trillion, which is more than the GDP of countries such as Japan, Germany, France, and the United Kingdom.

With the prospects of decreased employment, damaged infrastructure, and forgone revenue, it raises the question of whether or not we are willing to lose an ecosystem that benefits local economies so much. It’s not that the Great Lakes will cease to exist, but that the system will cease to be a sustainable habitat for not only plants and animals, but for ourselves as well.

Starting change

Seeing the consequences of our past actions shows how much of an impact our behavior can have. But how can we begin to undo the damage that we have done?

Canada and the United States have pledged to reduce the amount of phosphorus in the Great Lakes by 40 per cent by 2025. However, this goal has proven to be tougher to match now than it was in the past. Unregulated farms, dissolved phosphorus, and different phosphorus sources causing the algal blooms have made it harder for the countries to meet their targets. With the added threat of rising temperatures, the threat of algal blooms is imminent.

The Ontario Great Lakes Strategy 2016 progress report outlined the collective efforts of the government, scientists, Indigenous peoples, and private-sector organizations to work toward returning the Great Lakes to a state where they are not at risk of ecological collapse. However, governments have yet to impose hard-hitting restrictions on certain behaviours such as the use of phosphorus by the agriculture industry.

In 2018, then-Ohio governor John Kasich signed an executive order to restrict agricultural runoff, which contributes to algal blooms, by setting requirements for how nutrients in animal waste and fertilizer should be stored.

But government intervention isn’t the only source of change in our society. Organized groups of concerned citizens have a created huge impact on these pressing matters.

According to Shear, citizen activism has led to eradication of all sources of mercury in the Lake Superior Basin and to the cleanup of the Love Canal disaster in New York in the mid-twentieth century.

Love Canal was the site of a failed energy project that became a landfill, which was eventually buried and sold to the city for development. Decades later, chemicals began to seep up through the ground, exposing the region’s residents to carcinogens and teratogens, which are implicated in deforming embryos.

“It was citizen activism in Niagara Falls, Ontario that linked with citizen activists in Niagara Falls, New York that really brought [the provincial, state, and federal governments] to shut down Love Canal… to prevent the contamination of the Niagara River,” said Shear. “So citizen activism can really work.”

In building our cities, we did not plan to bring harm to our environment. Rather, we were careless and uninformed about how our actions could damage the very home we live in. As we learn about why these ecologically devastating events occur and how human activity causes them, we must take action to prevent further damage and restore what we can.

We could otherwise negligently trek forward and continue to make decisions that harm not only ourselves, but those who will come after us.

The flight of the monarchs

North America’s famous winged creatures travel 3,000 miles each year — but not a single one makes it back home

The flight of the monarchs

As green turns to gold and leaves kiss the ground, millions of monarch butterflies across North America prepare for a treacherous journey to the south. Their iconic black and orange wings colour the Ontario sky from June to late September.

The threat of winter’s bitter winds drives these insects to seek refuge elsewhere, but none of them return north.

Where do they go, and why won’t they return?

These questions haunted Fred Urquhart, a professor of zoology at UTSC and a giant in monarch butterfly research. Following decades of research, the work of his wife Norah, and a generation of citizen scientists, Urquhart and his team discovered the wintering place of monarch butterflies in Mexico in 1975.

Late September to October: heading south

As he stood alongside volcanic mountains in the Mexican state of Michoacán, Urquhart was in awe of the sight before him.

“I gazed in amazement at the sight. Butterflies — millions upon millions of monarch butterflies! They clung in tightly packed masses to every branch and trunk of the tall, gray-green oyamel trees. They swirled through the air like autumn leaves and carpeted the ground in their flaming myriads on this Mexican mountainside,” Urquhart wrote in National Geographic, one year after the discovery.

Most monarch butterflies that live to the east of the Rocky Mountains overwinter in Mexico, while those to the west head to California. The monarchs that migrate to Mexico overwinter in the mountains of a region known as the Transverse Neovolcanic Belt.

The migratory route of these insects is triggered by three environmental cues: shortening days, cooling temperatures, and aging milkweed, the main food source for larvae. Although these events tell monarchs when to migrate, there is no clear consensus as to how they find the same 800 square kilometre sweet spot in central Mexico year after year.

A promising theory suggests that the butterflies use the time of day and the orientation of the sun to guide their flight path. Monarchs could further be assisted by southward warm air currents, which create a convection in combination with cold air currents, and propel them forward without energy wastage.

To prepare for their journey south, monarchs enter a delayed maturity phase, or diapause. Diapause ensures that the butterflies do not start mating, but instead ration their time and energy by drinking nectar.

Late November to March: wintering in Mexico

The Oyamel firs in Michoacán are critical for species survival and reproductive success. This fir species serves as both an umbrella and blanket — it creates a forest canopy that prevents heat loss during the night and shields the butterflies from rain. The canopy further creates a cool microclimate, which slows the butterflies’ metabolism and conserves their energy.

Breeding monarchs have a lifespan of one month and require nectar, which is not readily available at nearby sites, to fuel their reproduction. To survive, the monarchs must remain in diapause until winter months have ended in their North American habitat.

The next generation of monarchs is laid on milkweed plants in northern Mexico by the overwintering butterflies in early March. Having shorter lifespans, they do not undergo diapause and breed on their way back north.

Late March to July: heading north

Second generation monarchs are laid throughout eastern North America from late April to June. The larvae extract nutrients from milkweed, undergo metamorphosis, and emerge from late June to early July. This generation also does not undergo diapause, and therefore can mate and reproduce. The third and fourth generations will populate most of southern Canada, and migrate once again to Mexico according to environmental cues.

Conservation

Monarchs are increasingly threatened by climate change, habitat loss, and agricultural insecticides. Variations in temperature affect their breeding and migratory routes. Habitat fragmentation due to the loss of oyamel fir trees degrades the microclimate that is essential to their survival. The use of neonicotinoid insecticides delays development and has been linked to behavioural changes and even deaths. Parasites such as O. elektroscirrha expose monarchs to infection during their journey, reducing their flight endurance and lifespan. In addition, 20 million butterflies die in car accidents on their way to Mexico every year.

Conservation measures have been put in place to mitigate these losses.

In 1992, Orley “Chip” Taylor founded Monarch Watch, a citizen science project devoted to tagging and tracking monarch butterflies during migration.

The Monarch Butterfly Biosphere Reserve, designated a UNESCO World Heritage Centre in 2008, protects monarch butterflies’ overwintering sites that lie northwest of Mexico City.

Urquhart once said that the monarch butterflies “reveal the resilience of nature and the relentless drive of all life to endure. Such fragile wisps of life and beauty are elegant symbols of the plight of all living things in a world of ecological change.”

We should do what we can to protect them.

Editor’s note (28/10): This article has been updated to reflect more accurate information about the wintering patterns and conservation of monarch butterflies, and the foundations of Monarch Watch.