Monitoring Monarchs & Milkweed

Monarch Caterpillar on Milkweed
Photo: @perkyleb

JULY 28, 2022 — My name is Emily, and I am one of the summer students with Nature NB, working alongside my co-worker Madeline as a Nature Educator. One part of our job this summer is visiting milkweed patches to look for evidence of Monarch butterflies. We wanted to share some of our findings from this project over the last three weeks to give some insight into the monitoring process, why this work is so important, and how to help protect this species at risk in the future.

Emily pictured left, Madeline pictured right. Photos: Emily Kenny

Milkweed is very important to Monarch butterflies because it is the only plant the caterpillars will eat. Sadly, some estimates suggest that over the past two decades, the Eastern Monarch population has declined by about 80% (1). Since 2019, Nature NB has been advocating for the conservation of monarchs in New Brunswick by monitoring milkweed patches, advocating against mowing, and creating awareness through educational events, programs, and social media.

Common milkweed pictured left, swamp milkweed pictured right. Photos: Emily Kenny

Throughout July and August, we have been travelling to milkweed patches in Southern New Brunswick to count monarch eggs, caterpillars, chrysalides and adults and to make note of the size and density of the milkweed patch and species of milkweed growing. We then submit our data to Mission Monarch — a citizen science site dedicated to collecting data on monarch populations in Canada.

Monarch butterfly life cycle, from left: egg, 1st instar, 2nd instar, 3rd instar… (Photos: Emily Kenny)

At the beginning of July, we were having a hard time finding signs of Monarch butterflies, but by mid to late July we were finding much more. In three weeks we surveyed 2178 plants and found 110 eggs and 9 caterpillars. We noticed a steep incline in observations by late July. For example, in a patch of 26 plants, we found 17 eggs and 1 caterpillar. We were excited to see this increase in numbers as monarchs continued to migrate into the province!

My favourite discovery so far was a caterpillar in its fourth instar! Caterpillars hatch from eggs and go through 5 stages of growth, called instars (As seen above in the life cycle). This process takes about 2 weeks before entering their chrysalis. It was the largest caterpillar I’ve seen so far this summer, and it was beautiful sitting on the flower of a milkweed plant.

Monarch life cycle continued: 4th instar, 5th instar, chrysalis, butterfly (Photos: Jordan Stone & Alysha McGrattan)

Through our observations, we realized that a milkweed patch contains a lot of diverse species, not just monarchs! Monarchs have predators, just like most other small, living things, and although they are a species at risk, this is a natural occurrence. Over the past three weeks, we have seen many predators on the milkweed plants.

Some of the species we observed utilizing milkweed may predate on monarch eggs and caterpillars: Twice-Stabbed Stink Bug, Goldenrod Crab Spider, and Oblong Runner Spider. (Photos: Emily Kenny)

We have also observed many insects that utilize milkweed but don’t harm the Monarchs. My favourite is the Milkweed Leaf Beetles. It resides on milkweed, and it eats the plants just like monarchs. This beetle has a very beautiful pattern that always catches our eye!

Swamp Milkweed Leaf Beetle larva (left) and adult (right). Photos: Emily Kenny

Overall, these past 3 weeks of monitoring milkweed patches in New Brunswick have been a fantastic learning experience. We have taken our findings and learned a great deal about the Monarch species as a whole, as well as the right conditions in which they need to live and maintain a healthy life cycle. Currently, we have only observed Monarch eggs and caterpillars and have yet to find any chrysalis, but we will continue to survey and hopefully find one this summer.

One of the best ways to support the Monarchs is to educate yourself, plant milkweed plants in your garden, refrain from using pesticides and herbicides, and advocate for leaving milkweed patches unmowed between June and September. For more information on getting involved with protecting the Monarch Butterfly population in New Brunswick, Nature NB has many resources and information available.