One of the world’s greatest migrations is now underway, that of the Monarch Butterfly. Weighing about half a gram, these incredible insects are embarking on a four-to-five-thousand-kilometre journey, a journey that they have never taken before to their wintering site in the mountains of Central Mexico. They usually arrive in late October to early November.
Although the average life of a Monarch Butterfly ranges from two to five weeks, the generation known as the Methuselah generation that we see this time of year lives for nine months or more, long enough to overwinter in Mexico, and start the journey back north in March to start the cycle all over again.
The migration cycle from Central Mexico here to Ontario and back to Mexico takes four generations to complete, so the butterflies that we see in late August and into September are completing the journey that their great grand parents began in late March.
During her short lifespan, a Monarch butterfly will mate and lay anywhere from 100 to 400 eggs. They usually lay only one egg per milkweed plant, the host plant of Monarchs.
Only about two percent of these eggs will make it through to the end of the adult stage, most succumbing to natural predation. Sometimes, a female Monarch will lay eggs on a plant related to the milkweed plant – European Swallow-wart also known as Dog-strangling Vine. Monarch larvae are totally dependent on Milkweed plants so if they hatch on Dog-strangling Vine, they will starve to death.
The Monarchs that are now preparing to migrate to Mexico have already overcome overwhelming odds.
Monarch Butterflies are a threatened species in Ontario. Besides the presence of Dog-strangling Vine in the area, other threats include deforestation of wintering habitat in Mexico, climate change, loss of Milkweed plants and native nectar plants along their migratory route.
We can help Monarch Butterflies by planting native species in our gardens. Milkweed species like Common Milkweed. Butterfly Milkweed and Swamp Milkweed can enhance the look of a flower garden and also provide a host plant for butterfly larvae. Late blooming plants like Black-eyed Susan, Purple Coneflower, Goldenrods and Asters provide the nectar needed for their long journey south.
Removal of Dog-strangling Vine on your property and along our trails can also greatly assist their survival.