Many of us enjoy searching for monarch caterpillars on milkweed in late summer and thinking about the next generation of beautiful monarch butterflies. Along the way, one may be surprised to encounter a lesser-known caterpillar getting its fill of milkweed alongside the monarch caterpillars. Milkweed tussock moth, Euchaetes egle, sometimes referred to as the milkweed tiger moth, specializes in milkweeds and dogbanes for larval food. One can find these cute (in my opinion) caterpillars munching away on common milkweed, Asclepias syriaca, at the South Carolina Botanical Garden.
Although the adult moth is not particularly exciting in appearance, the late instar caterpillar is quite striking: covered in dense tufts of black, orange, and white. Like monarch caterpillars, the bright, contrasting coloration of the milkweed tussock moth caterpillar signals that its body contains an accumulation of toxic cardiac glycosides from the plants it feeds on exclusively. Even more interesting is that these moths also have an organ that emits an ultrasonic sound, serving specifically to warn bats, a primary predator, of their noxious flavor.
Milkweed tussock moth caterpillars feed in clusters as early instars, and the caterpillars can cause an impressive amount of damage to plants with their strong appetites. Gardeners may be alarmed to see anything other than monarch caterpillars ravenously eating their milkweed. Questions such as “Are they harmful?”, “Should I remove these?” may arise. The answers are: Euchaetes egle are native insects thriving on the plants they have evolved to consume. Although they may devour some of your plants faster than the monarch caterpillars can, milkweed tussock moth caterpillars are not causing actual harm.
You can try removing these fuzzy little guys by hand if you are concerned that there will not be enough milkweed left to sustain your monarch visitors and are determined to reserve your supply. However, handle milkweed tussock moth caterpillars with gloved hands as the caterpillars have urticating hairs that can result in an uncomfortable rash.
It is important to remember that species diversity is necessary for a healthy ecosystem. I encourage you, especially if you have enough milkweed to sustain milkweed tussock moth caterpillars, to let them be. Feel good about providing habitat and resources for another species in your garden.