Pupa
Egg | Larva/Caterpillar | Pupa |
Adult
Just before they pupate, monarch larvae spin a silk mat from which they hang upside
down. The silk comes from the spinneret on the bottom of the head. As it sheds its
skin for the last time, the caterpillar stabs a stem into the silk pad to hang.
This stem extends from its rear end and is called the cremaster.
While
the process of complete metamorphosis looks like four very distinct stages, continuous
changes actually occur within the larva. The wings and other adult organs develop
from tiny clusters of cells already present in the larva, and by the time the larva
pupates, the major changes to the adult form have already begun. During the pupal
stage this transformation is completed. Many moth caterpillars (but not all) spin
a silken cocoon to protect them as pupae. Butterflies do not do this, and their
pupa stage is often called a chrysalis. While it is
fine to refer to the previous stage as either larva or caterpillar, it is not correct
to call a butterfly pupa a cocoon, since it does not have a silken covering.
Just before the monarchs emerge, their black, orange, and white wing patterns are
visible through the pupa covering. This is not because the pupa becomes transparent;
it is because the pigmentation on the scales only develops at the very end of the
pupa stage. This stage of development lasts ten to fourteen days under normal summer
conditions.
To learn about male and female morphology,
read this article from our 2005 MITC Newsletter.