The very hungry caterpillar

Turning garden pests into garden guests.

Most people think of gardening as a nurturing sort of activity, forgetting that gardeners must also ruthlessly defend their crops from creeping green invaders. My bloodthirsty gardener instincts are in full force when invasive weeds (such as creeping bellflower) or creepy-crawly pests (like the caterpillar of the white cabbage butterfly) threaten to devour my brussels sprouts. But in the summer of 2020, I discovered that sometimes it’s okay to host a pest intent on destruction. The new, very hungry visitors were caterpillars of the monarch butterfly and my new milkweed plants were their prey.

For the early part of my life, monarchs always seemed like storybook creatures, like narwhals or reindeer. (Some things never become real until one encounters them in real life.) But after moving to Northwestern Ontario, I began to learn about milkweed and monarchs, especially through the work of Dan Fulton, the founder of the Adelaide Monarch Garden in Thunder Bay. Monarch numbers have been declining for decades due to habitat loss, use of pesticides and climate change. Our region sits at the northern-edge of monarch territory, so many people plant milkweed (the necessary host plant) to help sustain the monarch populations as they prepare to make the 4,000-5,000 km migration back to Mexico for the winter. Between their arrival in spring and departure at the end of summer, three generations of monarchs will have called those milkweed plants home.

Gardening generously

In the summer of 2021, the monarchs arrived a few weeks early, when the milkweed plants were still quite small. The monarch-obsessed population of Thunder Bay watched with trepidation as female monarchs deposited egg after egg on plants that wouldn’t be able to sustain the resulting caterpillars. I had as many as 12 large caterpillars at a time eating away at a single milkweed plant, and by the time they were ready to leave to form a chrysalis, they had gnawed it down to the stems.

Far from mercilessly protecting my garden plants, I soon found myself offering more and more milkweed plants to be devoured by my new guests. I increased the number of milkweed plants in my yard from three in 2020 to eight in 2021 and added a new native plant garden in the alley beyond the fence. I’m hopeful that one day my milkweed will grow fast enough to outpace the caterpillars and put out flowers.

Eventually, the strange relationship between milkweed and caterpillar ends as each mature caterpillar departs on a journey across the yard to find a likely spot to build a cocoon such as on the underside of a rhubarb leaf, in the trellis behind the honeysuckle, or under the railing on the deck. I heave a sigh of relief that I grew just enough milkweed to provide each voracious teenager with the means to progress to its next stage. If I’m lucky, I’ll be around to watch it emerge and spread out its new wings. I guess I can sacrifice a few flowers for the monarchs and save my wrath for the little green cabbage worms.


  • Elisabeth Gesch

    Elisabeth lives in Thunder Bay, Ont. where she grows climbing plants up every available fence in postage-stamp sized yard and discourages her cat, Sharpie, from chasing after butterflies.

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