caterpillar identification GEHP

[Mike]

I think that you DID find either a luna or possibly a polyphemus.  When
luna's (and all pillars) are ready to pupate, they "clear thier gut",
then find a suitable place for pupation.  When luna's do this, they
change colors also.  I luna about to pupate is usually a rosy brown or
orangish color.  Now, you can tell a luna cocoon from a poly because
polys are usually very well formed egg shapes, while lunas are flimst,
papery, non-descript masses.  And, if opened, the pupae of the poly has
a "winow" on it's head and the luna will have a small strand of silk
attached from the cocoon to the cremaster (butt) of the pupae.  Hope
this helps.  I breen many lunas at my house here in MD, and it is the
most common Sat in my area.  LOTS of Sweetgum....thier favorite tree. 
Write anytime