Meet the Milkweed Tussock Moth Caterpillar
Paulette Greenberg, Anoka County Extension Master Gardener Intern
Most gardeners in Minnesota have answered the call to invite monarch butterflies into our gardens and yards by planting milkweed. It is important to make sure we know how to identify these iconic caterpillars as they munch their way into milkweed commas, so they can later become the orange and black beauties we love. However, what we may not know is that there is another lesser-known caterpillar who also loves milkweed just as much: the milkweed tussock moth caterpillar, aka the milkweed tiger caterpillar or Euchaetes egle.
A few summers ago, I was admiring my bumper crop of milkweed, which was much larger than I intended. Like many naïve gardeners, I planted it in my vegetable bed the year before and it had greedily sucked up real estate. I had already seen monarch caterpillars a few weeks earlier and was hoping to find any stragglers to make sure they were well-fed and on their way to a nice quiet place to cocoon themselves to their next stage of development. To my horror, I spotted a wriggling mass of orange, white and black bodies on several of my plants. These voracious noshers were much tinier than the monarch caterpillars I was accustomed to seeing, only about an inch or so and fuzzier. By the end of the day these mini piranhas had skeletonized entire plants. In a panic, I consulted my trusty I Naturalist app to identify these culprits, although it took me much longer to understand whether they were friends or foes.
It turns out that these hungry creatures are not bad; they are just misunderstood. Monarch caterpillars prefer younger plants for their meals. The milkweed tussock moth caterpillar comes along between July and August and they tend to eat the older plants left behind by the picky monarchs. Yes, they are essentially eating ‘the leftovers,’ and although it might look like they have destroyed the milkweed plant, I can tell you with great certainty that the milkweed does just fine and lives to send out many more babies the next year. If they bother you or you have limited milkweed, you can simply snip the leaf and set it someplace else. It is important to note that like the monarch caterpillar, their only food source is milkweed, so they won't ravage your other food or floral crops. I leave them, as they are natives to our eco-system.
I assumed that because these little eating machines were colored like a monarch that they must certainly be smaller versions of their cousins when they emerge in their winged glory. Sadly, that is not the case. The moths are quite non-descript but are no less important as pollinators. It is important to note that like the monarch, their only food source is milkweed, so they won't ravage your other food or floral crops, either. Now that I know more about them, I let them be and actually look forward to seeing them.
The Michigan State University Extension program has an article you can read to learn more about the Milkweed Tussock Moth Caterpillar: https://www.canr.msu.edu/news/milkweed_tussock_moth_larvae_feed_on_common_milkweed
The University of Wisconsin also has more information, and some great pictures as well: https://wimastergardener.org/article/common-milkweed-insects/