Make sure that you are checking plants carefully and thoroughly. Glance at the whole plant first to see if there are any caterpillars that you might knock off before taking a closer look. Middle and late instars tend to avoid predators by curling up in a ball and rolling/falling off the plant, and early instars, if disturbed, often fall from the plant and hang suspended on a small silk thread. While the different larval instars are often all around at the same time, you should be able to use your knowledge of monarch biology to deduce what you might see on a given date. We recommend checking out the stacked bar graphs on the MLMP Results page for your state. For example, egg-laying monarchs typically arrive in Minnesota between mid-May and early-June, so we are on close lookout for eggs during that time. As soon as we’ve found eggs, we know that in subsequent weeks of monitoring we could be finding caterpillars. Think about what you observed the week before and use that to determine what you might find this week. Keep in mind that you may have missed some and new eggs could be laid at any time! Do not record the stages of monarchs you think you SHOULD be seeing if you do not actually see them.
We keep an eye out for reports that don’t quite match up. For example, if you are seeing late instar caterpillars but never reported seeing any eggs, that is a cue to us that you might be missing eggs or that you were not monitoring when those caterpillars would have been eggs. If you find yourself finding larger caterpillars but never eggs or tiny first instar caterpillars, you’ll need to practice looking more closely for those eggs and early instars. Try a magnifying glass or small hand lens to magnify small dots on the milkweed plant that you aren’t sure about. Make sure you’re looking in all of the plant’s natural hiding places, like buds and flowers, and the top set of leaves that come together. While less obvious, small caterpillars also leave clues on the plant. Look for small semi-circles on the leaves (usually not on the outside of the leaves for early instars) where caterpillars have been chewing.
If you’re only seeing eggs and early instars and are finding very few later instar caterpillars, you probably aren’t missing anything! It is typical to find fewer later instars, as many of them don’t survive long enough to get very large. Researchers estimate that less than 10% of the eggs that are laid make it to adulthood.
Refresh your knowledge about monarch biology and instar identification by reviewing our our training video.