The life cycle of the butterfly follows the typical pattern of highly developed insects. A larva or caterpillar hatches from an egg in July, which then over the next two to three weeks develops into a stationary stage or pupa, also chrysalis. The pupal resting time starts at the end of July/beginning of August, and ends with the emergence of the adult butterfly, or imago, from May until the end of June. At this time the fertilized females lay their eggs singly on the leaves of the bistort plant.
Eggs are easy to find. They are deposited by the females on the undersife of bistort leaves in a distance of a butterflies body lenght. Eggs look like miniature golf balls, which is typical for the coppers. When you can identify a small hole in the middle of this golf ball, the young caterpillar is hatched. It is worth while searching for it, because they stay on their "cradle leaf" quite a long time. But be aware of their well developed camouflage.
Depending on its age, the caterpillars cause different feeding patterns. In the early stages they are only able to feed on the smoother parts. Mouth parts are not strong enough, yet. The uppermost cellular layer is indigestible for them. Thus they cause a characteristic mosaic like pattern. Since this layer is very thin the pattern remembers to an assemblage of small windows within the leaf.
Fully grown caterpillars are able to eat all leave parts.
Larvae of the Violet Copper look more like woolice than like typical caterpillars. The body is flattened and the legs are very short.
(two links on video clips showing a female during egg deposition)