chrysalis adaptive coloration

[Andria & James Wood]

   First of all, we are new to this list and to butterfly biology, but my
wife and I are intrigued.  We are hoping to ellicit some help from the
very knowledgable people that have assembled on this newsgroup.  We have
had 3 caterpillars, identified as _Papilio polyxenes_ (Black Swallowtail),
that fed on wild parsley and store-bought celery in a ten gallon tank
environment for several weeks.  There is a possible discrepancy in this
identification as the subsequent emergent (thusfar single) butterfly is
neither wholistically _P. polyxenes_ nor _P. glaucus_ (similar dark morph
Tiger).  I realize through investigating several references, that the
Swallowtail genera looks to be highly variable, but I have been unable to
locate a listing of morphological characteristics for defining a
particular species.  Phrasing such as "Usually has" and "might show" leave
room for speculation when considering wing patterning.  Thus said, the
following questions may not apply (or may shed light upon) the actual
species being dealt with, and perhaps further questions posed by
yourselves could shed light as to its specific or even subspecific
standing.
   We were astounded at the incredible cryptic grey (bark-like) coloration
of the first two chrysalis to form.  These mounted themselves on an open
(not covered by leaves on any side), verticle branch that was similar in
color.  Nothing was thought about this until the third chrysalis formed on
a smaller (diameter) Water Oak twig with leaves intact, and clustered with
others to make a concealed corner in the tank.  We were shocked at the
light green overall coloration of this chrysalis, and the yellow stripes
that replaced the black on the other two.  We thought that, since we
missed the initial formation of the first two, that perhaps this was a
phase and the coloration would slowly shift.  It has been three days now
with no apparent change.  This coloration most closely matches the
underside color of the Water Oak leaves.
   Is this apparent chameleon ability typical in butterflies, in the
genera, or just specific?  Do we know what external influences govern the
"decision" to morph into one color or the other, is it voluntary and is
the color potential limited to shades of these two basic pigments?  An
interesting note to us, but may be inconsequential, was the fact that the
third caterpillar was substantially darker than the first two.
   Any information that you could allow would be greatly appreciated.

-- 
    Andria & James Wood
     Birmingham, AL  USA
archilochus at mindspring.com