Pupa Discoloration

I found a caterpillar on my hollyhocks in September that was soon in a chrysalis. It wiggled for a while, but by the end of the month, the pupa darkened and didn't move at all. What happened?

—Helen Gilsdorf, Burlingame, California

Tom: Generally, if a chrysalis is green or brown it will remain that color until it develops and the butterfly emerges. I believe your chrysalis died, probably as a result of a parasite or disease, which was in the caterpillar when it went into that stage. The same thing can happen to moths as well. However, many moths form their pupa inside a cocoon, and you don't often know that the pupa is dead until it dries out and becomes very light.