Species of the Month, September 2022: Monarch Butterfly
by Adam Timpf
I think it’s safe to say that pretty much everybody is familiar with this black-and-orange migratory butterfly that winters in Mexico, and its association with native Milkweeds as the larval host plant here in Ontario. Sometimes people mistake the similar looking Viceroy for them, but overall, the general public can recognize Monarchs more than perhaps any other butterfly species we have.
Originally it was thought that the look-alike Viceroy benefits from this confusion since Monarchs are considered toxic and avoided by predators, conferring some protection on the Viceroy. This was often cited as an example of Batesian mimicry, where one palatable species gains protection by mimicking a harmful species. However, it has been discovered that Viceroys themselves are toxic, and thus this is an example of Mullerian co-mimicry, where both species benefit from looking like each other. When a predator samples a Viceroy or a Monarch, the predator will learn to avoid both species.
Monarchs have been in the news a lot lately as the IUCN (International Union for Conservation of Nature) has recently upgraded their status to endangered due to continued decline in their population. There are many different factors that have negatively affected them, but deforestation and human development of their wintering grounds are major threats. When so much of the monarch population is clustered together on a handful of acres in the mountains of central Mexico, it doesn’t take much to cause drastic declines. Climatic events, illegal logging, pests, disease – anything bad that happens on the wintering grounds has the potential to affect millions of individuals.
Of course, monarchs also have lots to contend with as they make their multi-generational migration north in spring. Extreme weather events like droughts, increasing development, intensification of agriculture, and widespread use of pesticides all play a role in habitat loss – which in turn limits how many Monarchs are able to reach Ontario each year. Once here, they reproduce, building in numbers throughout the summer, and it’s the final generation that then makes the pilgrimage south to Mexico.
Here in Ontario, Monarchs encounter another problem – the invasive Dog-strangling Vine. Monarchs will lay eggs on this plant, but the caterpillars are not able to complete their life cycle on it. To help combat this, many homeowners are taking it upon themselves to plant more native milkweeds around their yards and properties to help provide a safe haven for Monarchs to reproduce.
While the future of the spectacular monarch migration is up in the air, it’s unlikely the entirety of the species will go extinct. There are populations that winter in Florida, and many non-migratory populations throughout the Caribbean and South America. They are even found around the globe as non-native species where milkweeds have been introduced. Personally, I’m hopeful that conservation-minded folks from Mexico to Norfolk can help keep this Monarch migration going strong for generations to come through habitat protection, cultivation of host plants, and education and awareness.
Want to learn more and get up close and personal with Monarchs? Check out our Monarch Tagging event coming up on September 10, 2022.