top of page

Monarch Butterflies in the City

[Article written by Sylvia Sass]

Many pollinators need our help, but with butterflies, their future is especially concerning. They are facing significant habitat depletion and there is a substantial decline in nectar sources which are essential for their survival. To address this, many people have begun to rear butterflies. Rearing is the technical term for raising butterflies from the egg to releasing them into their naturel habitat.

Theresa, a local from London Ontario, was inspired by a friend, to rear butterflies and she has learned so much from this experience. Now she has a greater understanding of local pollinators, educated herself on the process of rearing, and has shared her knowledge about native plants best suited for nectar resources. I interviewed Theresa in the fall of 2020, and she explained the complete process and answered the questions I had on rearing butterflies.

The Process:

The most important thing to note about rearing butterflies is that when they are caterpillars, they only eat milkweed. Milkweed (sp. Asclepias) is a common plant that grows throughout London and can easily be found in a typical neighbourhood. Theresa notes that it is very important to rinse and clean the leaves you give to your monarchs. It is also strongly advised not to accept milkweed from an unknown source because of the possibility that pesticides or other chemicals have been sprayed on the plant.

First Instar:

To begin the process first look on the underside of milkweed leaves to find the small, white eggs (see inside red square). Once the process has begun, be sure to keep the milkweed fresh and healthy for the caterpillars. In the first instar the eggs take three to five days to hatch.

Second Instar:

The second instar begins once they are in their caterpillar form. This stage also takes three to five days. From this point on, the caterpillars begin to molt and grow bigger as they feed on milkweed.

Third Instar:

Once your caterpillars reach the third instar stage it is time to transfer them into an enclosure. The size depends on how many you are rearing but the average size is about 20 by 20 inches. Theresa has found that many people use mesh laundry hampers and place newspaper on the bottom to collect the frass (poop of the caterpillars). Be sure to clean daily to avoid build-up of waste. The photo to the left shows both third and fourth instar stages.

Fourth Instar:

Once again, the caterpillars have molted and now are about 13-25mm in length. Monarch caterpillars can also look very different in their outer appearances of black, white, and yellow stripes.

Fifth Instar:

After about two weeks your caterpillars have now begun to pupate and take their chrysalis form. This fifth instar stage can also be identified by the size of the caterpillars reaching 25-45mm in length.


Migration is a natural part of a monarch’s life and usually begins late in August and continues all the way into October. The monarchs’ flight south to Mexico takes about one month. Once they arrive, the monarchs have a lifespan of four to six months. Throughout the migration journey, Theresa explained that you can track your butterflies on their trip. Goderich Ontario is one core spot for tagging your butterflies. Monarchs Migrating through Ontario is a great Facebook page that is helpful for anyone who is interested in tagging butterflies, watching their journey, and having any question you may have answered. Once the monarchs have reached Mexico you have the option of searching your butterflies’ number and seeing if they made it. The locals there are payed $5 if they find butterfly tags from Canada. However, even though many butterflies do migrate, some stay the winter and hibernate by burrowing into the ground. They only come out once milkweed begins to grow again.

What we can do to help:

Words of advice from Theresa was to plant nectar resources producing in the fall. There are many spring and summer plants to collect nectar from but once fall begins, the plant diversity and population decreases and there is less food for the adult monarch. Some ideal plants are purple cone flower, Mexican sunflower, golden rod, and zinnias. She also suggests growing native plants to balance out the invasive non-native species. For further information, a great resource to keep learning about butterflies is MrLundScience’s YouTube channel.

Connect with Pollinator Pathways Project



bottom of page