In early August, as the summer was maturing, the green fields and gardens of Rappahannock County took on the warm tones of summer — mostly yellow and oranges, set off by black and white.
As I was walking my dog past a small patch of butterfly milkweed in one of my gardens at dawn one day in the first week of August, I noticed a mass of mostly black insects crawling around in the patch. The two affected plants had apparently finished blooming for the year, or at least paused their blooming, but I was hoping to get some of their seed pods to plant in other areas.
Unlike its more-aggressive cousin, common milkweed, butterfly milkweed spreads only by seed, not rhizome. I could see the third plant in the group still had some of the bright-orange blooms and no bugs . . . yet. It wasn’t light enough to see which insect species was defoliating the plants, so I decided to come back in a couple of hours, when the light would be better, to take a closer look.
I got busy on a deadline when I got back to my house, totally forgetting about the bugs in the milkweed until late afternoon. At that point, the little patch of milkweed was already in shade but I still hoped to get enough photos to help in identifying the tiny insects. When I arrived at the patch, the insects were eating the last of the foliage on the remaining milkweed plant. They formed a fast-moving eating machine, devouring the foliage and remaining blooms at an amazing speed.
In inspecting the quivering mass, I realized they were caterpillars —hairy ones, with tufts of orange and white hairs sticking out among shorter black ones, like little unkept tigers. In checking my favorite caterpillar guide, Princeton’s “Caterpillars of Eastern North America,” I discovered they were the larvae of a species of tussock moth, Euchaetes egle, commonly known, aptly, as the milkweed tiger moth, or as the milkweed tussock moth.
I’d never seen caterpillars feeding in such a frenzy. They were moving so fast and were so small (about a half inch) that I feared I wouldn’t be able to get a shot of them, especially as the light continued to fade. I fired away, trying to make a record of them before they were done. Within a few minutes, most had finished the rest of the milkweed foliage and disappeared among the neighboring thicket of aster and goldenrod. Only a few stragglers were weaving around at the ends of the bare plants looking for more food. They soon gave up and disappeared, too.
The only other milkweed on the property is another small patch of butterfly milkweed in my herb garden, about 10 feet from the patch the caterpillars had just destroyed, I wondered if such tiny little animals would find their way there over a mowed lawn but haven’t seen any sign they have.
Since I live in an area that is mostly forested, I had only a slim hope of attracting monarchs to my milkweed when I planted it. Although milkweeds are the monarch’s sole host, it generally prefers species other than butterfly milkweed, with common milkweed a favorite. I’d tried adding seeds of that species of milkweed to a nearby meadow garden last fall, but none came up this year.
Tussock moth and the monarch larvae may not really compete for milkweed as a host, as the author of the Princeton guide, David L. Wagner notes: “In my experience, the two insects commonly affect different sorts of plants. I associate monarchs with young, vigorously growing shoots, while milkweed tussock moths are content to eat older foliage, sometimes that which has already started to yellow.”
I figured the milkweed patch had at least helped host one lepidopteran species, although the fate of the caterpillars, in two early instars (growth stages), is still not clear. Despite the fact that tussock moths can be voracious, I love to watch them. Their distinctive tufts of hair vary in color from species to species. Although the hair of some can cause an allergic reaction in some people, it always makes me think of Yorkshire terriers. And as with Yorkies, it’s often hard to tell one furry end from the other.
The adult of this tussock moth species, as is often the case, is much less unimpressive than the caterpillar. About an inch and a half long, it has mousy gray wings but does retain a hint of the tiger: an orange body with black marks.
This moth ranges widely throughout the eastern United States and eastern Canada. Its only hosts appear to be milkweed (Asclepias) species and plants in a related genus, dogbane (Apocynum), both of which carry a toxin that a lot of other wildlife can’t tolerate. Although there are more than 100 species of both on the planet, here where I live only there are just the two small patches I planted. This doesn’t bode well for the little gang of caterpillars that demolished my butterfly milkweed. Unless they find my other patch, they’ll likely starve or become prey for the many predators here.
There be tigers in my milkweed slideshow:
© 2017 Pam Owen
On the hunt for caterpillars
A few days after I found the milkweed tiger moth caterpillars,, I visited Robin Williams to look for caterpillars in her butterfly garden and among other host plants she’s planted or conserved on her property in Slate Mills. She’d seen some that sounded interesting, including a saddleback, which is known for its amazing looks but even more for its amazing sting, which comes from chemicals on its barbed hair). However, we only found a some more larvae of the milkweed tiger moth munching away on Robin’s diverse milkweed species, along with a few mystery larvae.
In my research later, I could only ID one of the latter — a black-waved flannel moth caterpillar that, in the early instar we found it, looked like a wispy chunk of hair pulled from Santa Claus’ beard. I originally thought it was a yellow bear caterpillar, the larva of the Virginian tiger moth, whose color can range from light brown or grey to yellow or white. But the wispiness was more typical of the flannel moth in question. The other two larvae appear to be from sawflies.