First you need to find milkweed! Here where we have acres of common milkweed I can find it by following my nose. The sweet fragrance floats on the air. It might be possible to track one of the Monarch butterflies that are flying around, but they fly by pretty fast and Mrs. Monarch would rather deposit her eggs in a private unobserved location!
Once you know what milkweed looks like, look for a nice green tender looking plant that has been chewed on the edges. The black stuff on the leaf is another great clue. It is frass. That is just another way of saying caterpillar poop. Since it is black it is not fresh. More searching is necessary.
Caterpillars are not as speedy as butterflies though so a closer look at this plant is needed. There was a caterpillar here before, maybe he hasn't gone far! I spotted a leaf lower on the plant with what looked like fresh chewing. I don't see anything on the chewed leaf. Often the caterpillars are found on the underside of the leaves. That is where the eggs usually are. What I need now is a closer look! Let's set the camera on macro!
Eureka!!! This is not a big fat Monarch caterpillar, but a tiny instar. It is actually smaller than it appears in the picture. In fact I have never found a Monarch in such an early stage of development. This is exciting! Notice the frass on this leaf is not black, but green and watery. Now that is what I call a fresh clue! If you go back to the previous picture you might be able to notice the caterpillar. It was tiny, but right there in plain sight all the time.
This is the earliest I have found a Monarch caterpillar here. Ed follows a careful mowing program so that the milkweed flourishes and so that fresh green plants are available for the Monarchs to use right up until frost in the fall. Once the first caterpillar has been spotted, no matter how small, the mowing stops! I will be checking on this caterpillar and searching for more. Now that you know what to look for, find some milkweed near you and take a closer look.