Monarch and Milkweed Monitoring along the Mississippi River
By Erika Van Krevelen, Community Volunteer Ambassador 2021, Mississippi National River and Recreation Area
As I walked the perimeter of a prairie at North Mississippi Regional Park, I passed dozens of milkweed plants, none of which caught my eye enough to make me stop. The plants were less than a foot tall and a pale green, too early in the season for flowers, and there wasn’t a monarch in sight.
Common milkweed (Asclepias syriaca) on the Mississippi River. Photo credit: National Park Service / Gordon Dietzman
I found this absence discouraging, as monarchs have faced declining populations over the past 20 years, largely due to habitat loss in the places where they breed, migrate, and overwinter. I was also a half hour away from leading the first monarch monitoring event at North Mississippi with a group of volunteers. The Mississippi National River and Recreation Area has held similar monarch monitoring events for several years as part of the Monarch Larva Monitoring Program (MLMP), a community science project aimed at better understanding monarch population dynamics in North America by studying monarch and milkweed density. This was the first time monitoring at this location, however, and I was afraid there wouldn’t be much to see. I began preparing what I would tell the volunteers, who likely arrived eager to see the bright orange butterflies or the vibrant striping of the caterpillars, when we left that day with zeroes lining the columns of our datasheets. “’No data’ is still data,” my science mind reminded me, but still, I hoped to see more.
Swamp milkweed (Asclepias incarnata). Photo credit: National Park Service / Gordon Dietzman
I met the volunteers outside of the Carl W. Kroening Interpretive Center and we headed south to a large prairie, restored with a diversity of native plants that will provide a steady nectar source all summer long—a must for monarch butterflies. For our purposes, most important of these plants was the milkweed, as monarch caterpillars are picky eaters and choose only to munch on milkweed species. I warned the volunteers of the difference between common milkweed and the hemp dogbane that also grew in the prairie, since these two plants can resemble one another when young and both exude a milky sap known as latex. It is this latex that gives milkweed its name, and also provides monarchs with a superpower of sorts: it contains a chemical compound that makes the monarchs poisonous and bitter-tasting to potential predators.
Monarch egg attached to the underside of a milkweed leaf. Photo credit: National Park Service / Gordon Dietzman
Monarch caterpillars gain this yellow, white, and black banding only after they have begun eating milkweed leaves. Photo credit: National Park Service / Gordon Dietzman
We settled into a spot along the edge of the prairie to begin our search. Carefully lifting the leaves on our respective plants, we scanned all over, paying special attention to the undersides. This is where the adult females typically lay their eggs, hardly larger than a pencil tip. To my excitement, I saw a small dot on one of the first few plants I looked at. I took out a hand lens to confirm my find, as dried latex droplets can deceive the naked eye. Through its magnification I could see the telltale pointed tip and the ridges lining the surface of the dot; I had found my first monarch egg. And there were many more to find, along with tiny monarch larvae with black heads and no stripes—a sign that they are only recently emerged from their eggs. We also found larger caterpillars with their famous yellow, white, and black banding, which is a feature that only appears once milkweed consumption begins. Our datasheets filled up over the next hour, noting the eggs, larvae, and butterflies we were fortunate enough to see.
We can’t always expect to have an outcome like we did that day, and that’s part of why we are participating in the project—to increase our understanding of monarch populations over space and time and to explore possible reasons for the changes we observe. We can then use this research to inform management decisions, improve monarch habitat, and inspire monarch conservation in our communities. And there’s another benefit to this monitoring; it reveals to us a hidden world tucked under a milkweed leaf, so easily overlooked by the those quickly passing by. Our slow, deliberate search for monarchs inspires not only conservation efforts, but a sense of wonder as well.
This deep dive into monarchs and milkweed is a great example of the kind of content explored in our Go With The Flow newsletter. Each month the park's Community Volunteer Ambassador pulls together stories focused on the historical, cultural, and ecological interpretation of the Mississippi River's only national park.