gnus reading through all my nnml directories on startup

[Victor S. Miller]

Starting recently (probably after making some change that I don't
remember), when I start up gnus (v 5.10.6) it displays messages saying
that it's reading the directories /home/victor/Mail/... for all the
nnml files that I have.  This takes a while (since I have a lot of
directories).  Is there some reason that this is happening?  More
important, is there a setting that I can make in my gnus.el which will
stop this behavior?

Victor