To Rear or Not to Rear.. A Monarch.

By Matt Thomson

It’s one of North America’s iconic insect species and holds the record for the world’s largest insect migration – the Monarch butterfly, or scientifically known as Danaus plexippus. What is now a popular activity at home and in the school classroom is now a hobby that should be avoided according to the latest scientific evidence. It’s no secret. Their numbers are in decline and have reached another record low population since 2012. They’re in dire need of help. Many people, across multiple age generations, have responded to this news by gathering the Monarch’s eggs or caterpillars from Common Milkweed plants around their backyard or throughout the neighbourhood and then bringing them indoors to marvel at one of the most fascinating natural wonders. It can be an exciting moment when one catches a glimpse of tiny football shaped eggs or the white, yellow & black striped caterpillars on those soft, slightly fuzzy Milkweed leaves. 

Unfortunately this hobby is not a sustainable conservation strategy as it was once believed to be. There’s a problem when these caterpillars are kept in an indoor, climate controlled environment. The butterflies are emerging from their chrysalis with smaller wings compared to the butterflies that are developed outdoors in their natural environment. Sometimes their wings are deformed, either shriveled or wrinkled from which they cannot fly. This is also an indicator that the butterfly is infected with a highly contagious parasitic infection known as Ophryocystis elektroscirrha, though most of us just say OE for short. This means that the butterfly will not be able to migrate to Mexico and should be kept separate from the wild ones that are fit for migration (even nature needs social distancing). In general, the indoor captive-bred butterflies are weak and their “magnetic compass” is dysfunctional. We don’t want those genetic traits to pass on to future generations of butterflies. 

There are traditionally four generations of butterflies during an “annual cycle”. The Monarch butterflies that are gracefully fluttering our countryside during June are basically the great grandchildren of the butterflies that arrived here last year. The first generation is overwintering in an Oyamel Fir forest in the mountains of central Mexico. In late January or early February they will have a mating period as the weather warms up. Their lifecycle comes to an abrupt end about a week following a successful mating. Those eggs, larvae & then caterpillars will develop into adult butterflies several weeks later. By the end of March, this new generation is departing on their journey northbound. Upon arriving in the southern United States, the state of Texas is a popular area for the next mating period. When the next generation of butterflies emerge, they carry on northward to our area and much of the U.S. Midwest & Great Lakes region with some heading to the east coast. However with the effects of climate change creating a shorter winter season, these breeding cycles are beginning earlier which means we are seeing Monarchs arriving in Ontario sooner, in the month of May. This also means the butterflies are susceptible to extreme weather events such as floods & snowstorms (in the Mexican mountains). Since the Monarchs are arriving earlier, it also means we may see a “bonus” second (or fifth) generation emerging by early August. It is only this final generation of butterfly that is capable of fluttering the entire distance to central Mexico (approximately 4,000 km). Their dependency on Common Milkweed plays into why this happens. The toxic white “milky” sap they consume during the caterpillar stage helps build stronger and larger wings in the adult stage, in short. The sap is made of a substance called cardenolides which other animals, including us, cannot consume and therefore predations are lower. As a matter of fact, there’s an infamous online video of a Bluejay barfing up a Monarch butterfly. 

So if you see Common Milkweed around your yard or along the roadside, don’t think of it as a nuisance but rather a valuable plant that Monarchs are in desperate need of. Leave the eggs and caterpillars where they are and appreciate the sighting. Monarchs are a resilient insect and there’s hope they will recover in numbers- they have before. 

Matt Thomson is a local conservationist based in Severn and enjoys engaging the community through citizen science events & activities. You can find him on Instagram or Facebook, @ardtreanature