Monarch (Danaus plexippus)
Place observed
Former golf course area
Description
The Monarch is one of the largest butterflies in Quebec and it does not go unnoticed with its bright colors that seem to serve as a warning to predators. The male is slightly larger than the female and is distinguished by a spot on its midrib. It has a unique life cycle and can be seen throughout much of North America.
Status
In July 2022, this amazing migratory butterfly was added to the International Union for Conservation of Nature (IUCN) list of endangered species because of its alarming decline in North America. Its population is estimated to have dropped by 90% over the past 20 years. On May 13, 2023, the federal government also announced that it would add the Monarch to the list of species protected under the Species at Risk Act (SARA) and classify it as an "endangered" species. This new status of the Monarch will include the objective of preserving the habitats which are essential to its survival. Also, several Quebec municipalities, including Rosemère, have become "Monarch Friendly Cities" since 2015, in response to an initiative by the David Suzuki Foundation and Space for Life.
Reproduction
In June, the first adult Monarchs arrive in our region. The females seek out young milkweed plants to lay their eggs (usually only one egg per plant). After a maximum of 8 days, a caterpillar hatches. It feeds on the leaves of the milkweed plant, despite the toxic sap they contain, and itself becomes toxic to most vertebrate predators. Because it grows rapidly, it must go through 5 successive molts. It seems that only 10% of the caterpillars make it to the chrysalis stage which precedes the transformation into a butterfly.
In July, after the Monarchs from this first summer generation have completed a life cycle and reproduced, a second generation appears. This makes it possible to observe adults, eggs, caterpillars and chrysalises at the same time.
In August-September, the young Monarchs emerging from their chrysalises receive, thanks to the decrease in sunlight hours, the biological signal of the great migration. In order to save their energy for their long journey south, their reproductive organs do not fully develop.
They travel thousands of kilometers to spend the winter mainly in central Mexico, at the same resting place, where they form colonies of millions of individuals during the night. Monarchs gather there on large conifers (oyamels) for a period during which their metabolic activities are genetically programmed to slow down (diaposis). They reach this destination in late October and leave in March for the northward migration.
Habitat and Food
Milkweed, the sole host plant of the Monarch, grows in open areas such as fields, dry meadows and roadsides. In Rosemère, available data indicates that many plants grow naturally in the area of the former golf course...and where milkweed plants are found, Monarchs are likely to be present.
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