Leonard Weber

August 28, 2023

It is widely known that milkweed leaves are eaten by the Monarch butterfly caterpillar. What is not so well-known is that another colorful caterpillar also feeds on the leaves of the Common Milkweed.

August is a good time to seek an introduction to the Milkweed Tussock Moth caterpillar.

There are many milkweed plants in Eliza Howell Park and I often check a few to look for insect activity. One of the insects I am hoping to see is the Monarch caterpillar.

Earlier in August this year, I noticed that some of the milkweed leaves on one plant had been partially eaten. When I looked underneath one leaf, I found dozens of caterpillars — Milkweed Tussock Moths.

They were very tiny, magnified in the next photo for a better look.

They are eager eaters, but they carefully avoid eating the leaf veins, apparently so that they do not get too much of the latex-like sap.

The caterpillars go through several stages of growth. When I next saw them, recently, they were much larger, very different looking, and feeding one or two at a time on nearby milkweeds. They were now eating the smaller leaf veins.

The Milkweed Tussock Moth is sometimes called Milkweed Tiger Moth because of the coloring. Like the Monarch caterpillar, it acquires some toxicity from the milkweeds, and (some? most?) predators have learned not to eat it.

When it reaches full size, the caterpillar goes into a cocoon, where it spends the winter, emerging as an adult in the spring.

The adult moth is mostly gray-brown, much less colorful. It is active primarily at night and I have no photos of it to include here. It is the caterpillar, not the adult moth, that is memorable.

This August I have been enjoying getting to know the Milkweed Tussock Moth caterpillar much better.

When I check milkweed leaves for caterpillars now, I am no longer thinking exclusively of Monarchs.