This is not the season for butterflies here up north, but as J.M. Barrie said, "God gave us memory so that we might have roses in December." So let's do this now.
The screencap comes from an online presentation this past year by Dr. Karen Oberhauser, director of the University of Wisconsin's arboretum. The chart at the left shows cumulative data from a project done under the auspices of the Monarch Larva Monitoring Project. Citizen scientists monitored a couple hundred milkweed plants at the arboretum, recording the presence of eggs, then larvae in their various stages, and finally the pupae (chrysalises).
The results exactly mirror the experience we have seen in our suburban home (which also has a hundred+ milkweeds). The Monarchs arrive from down south in May, at about the same time the milkweeds are emerging. We find some eggs on our plants then, but the real burst occurs in July, when the adults from the first batch have mated and oviposited. There is probably a third "peak" embedded within the decline of the second one, but the overall pattern is quite predictable. There is more data that can be derived from this chart re mortality and predation, but the overall pattern is I think worth sharing.