The eggs are barrel-shaped with about fifteen
conspicuous ribs down the sides, and numerous fine ridges at right angles to
these. They are laid singly on the upper surface of the leaves of the Garry
Oak Quercus garryana in May. At first pale green, they later turn orange,
and after a few days the first-instar caterpillar emerges. After its first ecdysis,
the caterpillar is pale green with a black head., and it has a characteristic
mode of feeding, constructing a shelter, and feeding. From the edge of a leaf
it bites two grooves obliquely inward from the edge, the grooves almost but
not quite converging together where they meet a small leaf-vein. This leaves
a triangular fragment of leaf attached by one vertex. It folds two sides of
the triangle over itself to form a comfortable retreat. The caterpillar rest
with its head turned to one side facing to the rear. In the final instar, the
head is reddish-brown, constrasting with the green body. The head is large,
and resembles a shower-cap.
A few caterpillars will pupate in the summer, the butterflies emerging shortly afterwards, but the majority of the caterpillars go into diapause for the winter, at which time they become a rather deathly-looking dirty white. They pupate in the spring, and butterfly emergence may take place anything from a few days to a few weeks later. The shiny pale green pupae have two curious black projections on the back of the head.
Some of the spots on the wings of the adult are translucent.
This butterfly is becoming much scarcer than in former times, mainly because the Garry Oaks are being defoliated or otherwise spoiled year after year by unimaginable numbers of other insects such as the moths Operophtera brumata, Malacasoma californicum, Chionodes trichostola and the gall wasp Neuroterus saltatorius.