You would be hard-pressed to find someone who doesn’t think of Monarch butterflies at the mention of milkweed. Funny name too when you think about it. In West Michigan, Monarch butterflies are facing a deadly threat from a growing invasive species: black swallow-wort. Last night, I met with Jessie Schulte, a land management expert from Blandford Nature Center and Master Naturalist Ginny Wanty from the West Michigan Cluster of The Stewardship Network to learn more.
We need to talk a little biology, so bear with me. Monarch butterflies have various sensors on their body known as chemoreceptors. A chemoreceptor translates chemical stimuli from outside the body into action potential in the nervous system. In English, they allow them to taste and smell. Now, we think of taste and smell at a high level in terms of our likes, dislikes, food, perfume, and certain streets in Chicago.
From a scientific perspective, taste and smell are signals sent to our brain telling us that a certain chemoreceptor has noticed a particular chemical. If this sounds confusing, that’s okay. You already know some of your chemoreceptors by another name: tastebuds.
For Monarchs, these sensors are finely tuned to recognize a chemical released by milkweed. The fluttering insects are drawn to the plant like a bull to the color red. Monarch larvae eats milkweed exclusively, so the plant is important for their survival.
In this analogy, if the milkweed plant is the color red, the black swallow-wort is the matador waiting to pull the cape away. It tricks the chemoreceptors. If given a choice between the two, a Monarch will land and deposit their eggs on the swallow-wort, Wanty explained. Why is this a problem? Black swallow-wort is toxic to Monarch larvae. By the way, it is also toxic for cats, dogs, and livestock.
The Kudzu of the North
“I like to call it the Kudzu of the North,” Jessie quipped. Waxy pointed leaves grow opposite from narrow, elongated seed pods. The vine grows thick like Kudzu, wrapping around itself back and again. Black swallow-wort is native to Eurasia.
A thick infestation can produce over 2,000 seeds per square meter of plant growth. And not only do the seeds disperse quite effectively through the air, but the plant also grows via underground stems called rhizomes.
Oh, and the flowers are self-pollenating. As you can imagine, it overwhelms and crowds out native species quite quickly and effectively.
What do I do if I find black swallow-wort?
Report it. Where? Through the Midwest Invasive Species Information Network (MISIN). It is best to leave treatment work to trained professionals. Well-meaning attempts to deal with invasive species without proper training can be a major source of their spread when done incorrectly. Early detection and prevention is key. You can help make a difference.
It spreads. Fast and far. You may not have pets, but your friends, family, and neighbors do. They need your help to prevent black swallow-wort from becoming prevalent and hurting not only the environment and economy, but pets and other animals.