As you can see from the above photo, the chrysalis (pupa) is changing from that light green to more translucent, which means that it will become a Monarch soon.
One likely reason, according to Mission Monarch: "The reproductive organs of the butterflies that emerge (go from pupae to adults) in late summer don’t fully develop. That allows them to save energy for their long flight to their wintering grounds, where they start arriving in late October and stay until March."
Also, according to Journey North: "The ones that migrate live longer, from August or September to about April (although a lot die before this).
When people hear this, they say they’d rather be migratory monarchs, but these butterflies probably face many more risks, and are likely to have a smaller chance of getting offspring into the next generation."
The migrating Monarchs feed on Goldenrod and Asters and gain weight as they go.
The library has at least three Monarch chrysalises. Check them out before they become butterflies and head south.
If you see Monarchs when visiting a hawk watch in the coming weeks, you can often see Monarchs migrate.