Thu. Feb 29th, 2024
Monarch Butterfly on flower.

Today’s post was written by summer student Danielle Bullen from Rondeau Provincial Park.

It’s that time of year again and all over Ontario we are starting to see those beautiful orange and black wings.

Monarch butterflies come from Mexico over a few generations, depending on the amount of milkweed available during their travels, and spend the summer here in Ontario.

From egg to chrysalis

Female monarchs (those without dark spots on their wings) lay, on average, 700 eggs over two to five weeks in August. These eggs are the size of the head of a pin!

butterfly on milkweed

Monarchs lay their eggs on common milkweed plants, usually on the undersides of leaves. They usually lay only one egg on a milkweed. After about four days, monarch caterpillars hatch from their eggs.

Over the course of their 10 to 14 days as larvae, these caterpillars grow up to 3,000 times their weight and shed their skin five times. Curiously, their skin is part of the food that makes them multiply their weight.

Monarch caterpillar eating milkweed,

Before monarch caterpillars pupate, they spin a silk mat and hang upside down from their last pair of legs in the shape of the letter J. However, they do not spin a silk cover around their pupa, meaning it is not called cocoon. but rather a chrysalis.

Monarchs develop in their pupal stage for about 10 to 14 days, depending on weather conditions. Near the end of a monarch’s pupal stage, the chrysalis changes from a bright green to a light color through which the orange and black of the adult monarch’s wings can be seen.

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Once the adult butterfly “hatches” from its chrysalis, it pumps fluid into its wings and, within a few hours, it is ready to take flight!


Adult monarchs that hatch in late August in Ontario have their work cut out for them. Since they cannot survive the Canadian winter, they must fly 3,000 kilometers to central Mexico for the cold season. These monarchs live up to nine months, much longer than those in early summer.

Labeled Monarch Butterflies

Here in Rondeau, we tag migrating monarchs using monarch clock. The butterfly tag is about the size of an eraser on the tip of a pencil. It is placed on the outside of the monarch’s wing, in the mitten-shaped cell. The tag contains a number that can be called if the monarch recovers in Mexico.