Monarch (Danaus plexippus)

The Mysterious and Marvellous Monarch:

Imagine for a moment, a colourful, four-winged insect, weighing a mere .5 grams (less than a penny), with a brain the size of a pinhead, on an epic journey in late September from the splendour of Canada to the lush transvolcanic mountain range of Mexico. It covers a distance of 3,500 km, averaging 75 kilometres of daily travel and takes two months to complete the voyage. What’s even more incredible is that the insect has never been to Mexico. Yet, somehow – in one of life’s mysteries – it is able to successfully complete the journey, joining millions of others. This insect is none other than, the most easily recognized butterfly in Canada, the beloved and marvelous Monarch.


Monarchs are in trouble. The overwintering numbers in Mexico the past few years are at an all time low. Habitat loss, pesticide and herbicide use in Canada and USA and illegal logging in Mexico have all contributed to the monarchs’ plight. In addition, severe weather changes (droughts, cold winters, early frosts) throughout North America have also had an impact. On a positive note, its only host plant, milkweed, as of April 2014 has been de-listed from the Ontario Noxious Weed Act.

Life Cycle:

Monarch Butterflies have a unique life cycle of a complete metamorphosis: from an egg, to a larvae (caterpillar), to a chrysalis and finally to an adult butterfly.


The female lays her eggs solely on milkweed plants. One small conical, cream-coloured egg, adorned with ridges, is laid, usually on the underside of a milkweed plant. The egg phase lasts about 3-8 days. Just before emergence from the egg, the tip of the egg casing will take on a black colour.

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The newly emerged larvae (caterpillar) measuring about 2mm, consumes the egg casing as its first meal. This is followed by devouring a small hole in the middle of the leaf. After that, it roams the milkweed plant and begins to feed on the leaf edges. Its voracious appetite will see its grow more than 3,000 times its egg mass size when it reaches full size of 5cm, undergoing a series of 5 instars (molts) – where it sheds its old exoskeleton (skin). The larvae stage lasts about 10 – 14 days.

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At the end of its larvae stage, it wanders around looking for a suitable place to pupate. It creates a silk pad (known as a cremaster), attached to the underside of a leaf or branch. Once securely attached it will shed its final exoskeleton. The chrysalis is a beautiful ornamental green complimented with a row of golden flecks near the top and a few at the bottom.  The chrysalis stage lasts about 9 – 15 days.

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Emergence usually takes place early morning. About a day or two before emergence, the chrysalis turns black, and the distinctive orange/black/white wing colours can be seen. Several hours after pumping blood throughout its body, the adult monarch is ready to take its first flight. The Monarch is one of our largest butterflies with a wing span of 93-105 mm. Males are easily distinguished from females by the two distinct dots on their hindwings. Adults live for about 2-4 weeks. Their purpose is to feed and mate. From May to late summer and early fall we may see up to 3 generations of monarchs in Southern Ontario.

The final generation, the one that emerges late summer and into September, is the one that will migrate to Mexico. Though they may look the same as any other Monarch they are quite different inside as they are genetically wired to migrate and enter a phase known as “diapause”, where their reproductive functions are turned off. Diapause allows them to conserve the necessary energy for the long journey ahead of them. Another interesting fact is that the final generation of Monarchs has a life span of almost 9 months!


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Unique Migration:

Arrival in Mexico:

The timing of the Monarchs arriving in Mexico coincides with, “Los Dias de Mueretos” (Day of the Dead). This ancient ritual is celebrated throughout Mexico on November 1 – 3. Mexican families make their way to cemeteries to picnic, party, and celebrate the life of those departed. The returning of the Monarchs is believed to represent to the old souls returning home to the sacred mountains.

Overwintering Roosts:

The Monarch roosts occur in an environment suited for their winter survival. The Oyamel Fir forests, located some 3,000 metres above sea level on the steep mountainside provide this environment. On average, Monarchs spend 154 days on their mountainside roosts. Sometime in February or March, the diapause switch is turned off, and the Monarchs become sexually active. The adults will disperse toward Northern Mexico and Southern Texas where the females will deposit eggs on newly emerging milkweed plants. The adults will die as they start to head northward. The new generation will start the cycle over and makes it way to Canada over a series of 3 – 4 generations.

Monarch Status:

Monarchs have been listed as a “Species of Special Concern” by COSEWIC (Committee on the Status of Endangered Wildlife in Canada).

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