Milkweed tussock moth caterpillars not to be confused with monarchs

If you don’t already appreciate a good tussock - a tuft of grass or sedge that invites you to sit upon it, you should. According to Merriam-Websters’ Dictionary a tussock is a compact tuft, especially of grass or sedge. When you hear this term, combined with moth caterpillar, one immediately envisions a hairy caterpillar, covered with bristles, somewhat like an ottoman, inviting to sit upon — at least that’s what I think. This image makes me love tussock caterpillars — they look like something from the world of Dr. Suess — a walking, colorful piece of furniture perhaps.

A friend recently found some caterpillars on the milkweed near her house in Dover, N.H. Their color, the fact that they were feeding on milkweed, and their tufti-ness made it very clear that these were milkweed tussock moth caterpillars. These are frequently confused with monarch caterpillars, not because they look alike but because they both specialize in eating milkweed. While monarch caterpillars are smooth and colorful, the tussock moths caterpillars are hairy and colorful. Both types of caterpillars are armed with black, white and orange/yellow stripes that let predators know to beware. This is where their story gets interesting.

Milkweed is an interesting plant. It gets its name from its sticky white sap. Break off a branch and you’ll see it ooze out. That white sap is reported to be a great cure for warts — I’ve tried it — let it cover your wart and it will disappear in weeks (which it probably would have anyway). The sap is an interesting chemical brew that can both help and hurt the young caterpillars. It is sticky and can actually trap and choke young insect larvae that feed upon it, those that survive benefit from the toxic chemicals found in the sap.

Both monarch butterflies and tussock moths benefit from eating milkweed. They can sequester the toxins found in the sap; cardiac glycosides that can kill most animals (humans included) if ingested in high enough concentrations. They even retain these toxins after they metamorphosize into adults. The warning coloration of the larvae - orange, black and white - is known by many insect predators who learn to steer clear at an early age.

As a teacher, I’m always on the lookout for milkweed plants and a bright green monarch chrysalis dangling down. Since learning about tussock moth caterpillars, I have a whole new appreciation for this plant and the insects it hosts.